THE EVOLUTION OF MAN. 



Ilntcrnational Science Xibrar\> 



THE 

Evolution of Man 

A POPULAR EXPOSITION 

OF THE 

Principal Points of Human Ontogeny and 

Phylogeny 



FROM THE GERMAN OF 

ERNST HAECKEL 

PROFESSOR IN THE UNIVERSITY OF JENA, 
AUTHOR OF "the HISTORY OF CREATION," ETC. 



IN TWO VOLUMES 

VOL. M. 



Ube Merner Company 

1&oo\^ /IDanufacturerg 

Bftrout ©bio 



Authorized Edition 



MADE BY 

THE WERNER COMPANY 

AKRON, OHIO 



CONTENTS OF VOL. II. 



List of Platei ••• ••• •^ — ••• •*• ^^ 

List of Woodcuts ... ••• ••• ••• ••• ^^^ 

List of Genetic Tables ... .m ^m m* ••• xvii 



CHAPTER X\. 

THE DURATION OF HUMAN TRIBAL HISTORY. 

C!omparison of Ontogenetic and Phylogenetio Perrodg of Time. — Dora- 
tion of Germ -history in Man and in Different Animals. — Extreme 
Brevity of the Latter in Comparison with the Immeasorable Long 
Periods of Tribal History. — Relation of this Rapid Ontogenetic 
Modification to the Slow Phylogenetio Metamorphosis. — Estimate 
of the Past Duration of the Organic World, founded on the Belatire 
Thickness of Sedimentary Rock-strata, or Neptanian Formationi. 
— The Five Main Divisions in the Latter : I. Primordial, or 
Archilithic Epoch. 11. Primary, or Palaeolithic Epoch. III. Second- 
ary, or Mesolithic Epoch. IV. Tertiary, or Cssnolithio Epoch. 
V. Qaatemary, or Anthropolithic Epoch. — The Relative Dnration 
of the Five Epochs.— The Results of Comparative Philology as 
Explaining the Phylogeny of Species. — The Inter-relations of the 
Main Stems and Branches of the Indo-Germanio Languages are 
Analogous to the Inter-relations of the Main Stems and Branches 
of the Vertebrate Tribe. — The Parent Forms in both Cases are 
Extinct. — The Most Important Stages among the Human An- 
eestral Forms. — Monera originated by Spontaneous Generation. 
— Neeesniy of Bpontaneovs Qeneration 



▼1 OONTENTB. 

CHAPTER XVL 

THK ANCESTEY OF MAN. 
L Fbom thb Moneba to thb Gastbaa. 

FAOl 

Relation of the General Inductive Law of the Theory of Descent to 
the Special Deductive Laws of the Hypotheses of Descent. — Incom- 
pleteness of the Three Great Eecords of Creation : Palaeontology, 
Ontogeny, and Comparative Anatomy. — Unequal Certainty of the 
Various Special Hypotheses of Descent. — The Ancestral Line of 
Men in Twenty-two Stages : Eight Invertebrate and Fourteen Verte- 
brate Ancettors. — Distribution of these Twenty-tw© Parent-forms 
in the Five Main Divisions of the Organic History of the Earth. — 
First Ancestral Stage : Monera. — The Structureless and Homo« 
geneons Plasson of the Monera. — Differentiation of the Flasson 
into Nucleus, and the Protoplasm of the Cells. — Cytods and Cells 
as Two Different Plastid-forms. — Vital Phenomena of Monera. — 
Organisms without Organs. — Second Ancestral Stage : Amoebse. 
— One-celled Primitive Animals of the Simplest and most Un- 
differentiated Nature. — The Amoeboid Egg-cells. — The Egg is Older 
than the Hen. — Third Ancestral Stage : Syn-Amoeba, Ontogeneti- 
cally reproduced in the Morula. — A Community of Homogeneous 
Amoeboid Cells. — Fourth Ancestral Stage : Planaea, Ontogeneti cally 
reproduced in the Blastula or Planula. — Fifth Ancestral Stage : 
Gastraea, Ontogenetically reproduced in the Gastrula and the Two- 
layered Germ-disc. — Origin of the Gastraea by Inversion (^invagi- 
natio) of the Planssa. — Haliphysema and Gastrophysema. — Extant 
Gastrssada ... ... ... ... .^ ... 94 



CHAPTER XVIL 

THE ANCESTRAL SERIES OF MAN. 

n. Fbom the Pbimitiye Wobm to the Skulled Animal. 

The Four Higher Animal Tribes are descended from the Worm Tribe. 
— The Descendants of the Gastraea; in one direction the Parent 
Form of Plant- Animals (Sponges and Sea-Nettles), in the other 
the Parent Form of Worms. — Radiate form of the former, Bilateral 
form of the latter. — The Two Main Divisions of the Worms, 
Acoelomi and Coelomati : the former without, the latter with, a 
Body Cavity and Blood-vessel System. — Sixth Ancestral Stage : 
Arohelmiuthea, most nearly allied to Tnrbellaria. — Descent of the 



C0NTEKT8. tH 



rAo« 



Coelomati from the Accelomi. — Mantled Animals {Ttmicata) and 

Chorda- Animals (Chordonia). — Seventh Stage: Soft- Worms (Scole. 
cida). — A Side Branch of the latter : the Acom-Worm (Balano- 
glossus). — Differentiation of the Intestinal Tnbe into Gill-intes- 
tine and Stomach-intestine. — Eighth Stage : Chorda- Animals (Chor- 
donia). — Ascidian Larva exhibits the Outline of a Choi-da- Animal. — 
Construction of the Notochord. — Mantled Animals and Verte- 
brates as Diverging Branches of Chorda-Animals. — Separation of 
Vertebrates from the other Higher Animal Tribes (Articulated 
Animals, Star-Animals, Soft-bodied Animals). — Significance of the 
Metamerio Formation. — Skull-less Animals (Acrania) and Skulled 
Animals (Cra/niota) . — Ninth Ancestral Stage : Skull-less Animals. 
— Amphioxus and Primitive Vertebrate. — Development of Skulled 
Animals (Construction of the Head, Skull, and Brain). — Tenth 
Ancestral Stage : Skulled Animals, allied to the Cyclostomi (Mywi- 
noidcs and Petromyzonidoe) ... m« ^m m* ••• 71 



CHAPTER XVIII. 

THE PEDIGREE OF MAN. 

m. Fbom the Pbimitivb Fish to the Amniotic Animal. 

Comparative Anatomy of the Vertebrates. — The Characteristic Qualities 
of the Double-nostrilled and Jaw-mouthed : the Double-Nostrils, 
the Gill-arch Apparatus, with the Jaw-arches, the Swimming- 
bladder, the Two Pairs of Limbs. — Relationship of the Three 
Groups of Fishes : the Primitive Fishes (^Selachii), the Granoids 
(Qanoides), the Osseous Fishes (Teleostei). — Dawn of Terrestrial 
Life on the Earth. — Modification of the Swimming-bladder into 
the Lungs. — Intermediate Position of the Dipneusta between the 
Primitive Fishes and Amphibia. — The Three Extant Dipneusta 
(Protopterus, Lepidosiren, Geratodus) . — Modification of the Many- 
toed Fin of the Fish into the Five-toed Foot. — Causes and Effects 
of the latter. — Descent of all Higher Vertebrates from a Five-toed 
Amphibian. — Intermediate Position of the Amphibians between the 
Lower and Higher Vertebrates. — Modification or Metamorphosis of 
Frogs. — DiSerent Stages in Amphibian Metamorphosis. — The 
Gilled Batrachians (Proteus and Axolotl). — The Tailed Batrachians 
(Salamanders and Mud-fish). — Frog Batrachians (Frogs and 
Toads). — Chief Group of the Amnion Animals, or Amniota (Reptiles, 
Birds, and Mammals). — Descent of all the Amniota from a Common 



• •• 



nn CONTENTa 

PAOR 

Lizard .like Pttrent-form (Protanmion) . — First Formation of the 
Allantois and of the Amnion. — Branching of the Amnion Animab 
in Two Lines : on the one side, Beptiles (and Birds), on the other 
side, MammalB ... ... ... m* m* ••• 107 



CHAPTER XIX. 

THE PEDIGREE OF MAN. 

lY. From the Fbimxtiyb Mammal to thi Apb. 

The Mammalian Character of Man. — Common Descent of all Mammals 
from a Single Parent-form (Promammalian). — Bifurcation of the 
Amnion Animals into Two Main Lines : on the one side, Rep- 
tiles and Birds, on the other, Mammals. — Date of the Origin of 
Mammals : the Trias Period. — The Three Main Groups or Sub- 
classes of Mammals : their Genealogical Relations. — Sixteenth 
Ancestral Stage : Gloacal Animals (IToTto^r&mata, or Omithodelphia), 
—The Extinct Primitive Mammals (Promo/mmaUa) and the Extant 
Beaked AnimitlH (Omithostoma) . — Seventeenth Ancestral Stage: 
Pouched Animals {McurtupiaUa, or Didelphia). — Extinct and Extant 
Pouched Animals. — Their Intermediate Position between Mono- 
tremes and Placental Animals. — Origin and Structure of Placental 
Animals (PlacentaUoj or MonodeVphia). — Formation of the Pla- 
centa. — The Deciduous Embryonic Membrane (Decidua). — Group 
of the Indecidtia and of the Decid/uata. — The Formation of the 
Decidua (vera, serotina, reflexa) in Man and in Apes. — Eighteenth 
Stage: Semi-apes (ProBimice). — Nineteenth Stage : Tailed Apes 
{Menocerea). — Twentieth Stage : Man-like Apes (Anthropoides), — 
Bpeeohleu and Speaking Men (Mali. Hominet) ,„ .^ 140 



CHAPTER XX. 

SUB raSTOBT OF THE EVOLUTION OF THE EPIDERMIS AND 

THE NERVOUS SYSTEM. 

Animal and Vegetative Organ.systems. — Original Relations of these to 
the Two Primary Germ-layers. — Sensory Apparatus. — Constituents 
of Sensory Apparatus : originally only the Exoderm, or Skin-layer ; 
afterwardfl, the Skin.oovering specialized from the Nerve-system. 
— ^Doable Function of the Skin (as a Covering and as Organ of 



CX)NTENTa Ix 

rAOB 

Touch). — Outer Skin (Epidermis) and Leather-skin (^Corium). — 

Appendages of the Epidermis : Skin-glands (Sweat-glands, Tear- 
glands, Sebaceous Glands, Milk-glands); Nails and Hair. — The 
Embryonic Wool-covering. — Hair of the Head and of the Beard. — 
Influence of Sexual Selection. — JSLrrangement of the Nerve-system. 
— Motor and Sensory Nerves. — Central Marrow : Brain and Dorsal 
Marrow. — Constitution of the Human Brain : Large Brain ((7«f>»- 
hrum) fjid Small Brain {Cerebellum). — Comparative Anatomy of 
the Central Marrow. — Germ-history of the Medullary-tube. — Sepau- 
ration of the Medullary-tube into Brain and Dorsal Marrow. — 
Modification of the Simple Brain-bladder into Five Consecutive 
Brain-bladders : Fore-brain (Large Brain, or Cerebrum), Twixt- 
brain ("Centre of Sight"), Mid-brain (" Four Bulbs "), Hind-brain 
(Small Brain, or Cerebellum), After-brain (Neck Medulla). — Yarious 
Formation of the Five Brain-bladders in the various Vertebrate 
Classes. — Development of the Conductive Marrow, or "Peripheric 
Nervous System " ... ,., „, . ,^ »^ ,,, 190 



CHAPTER XXL 

DEVELOPMENT OF THE SENSB-ORGANa 

Qrijfin of the most highly Purposive Sense-organs by no Preconceived 
Purpose, but simply by Natural Selection. — The Six Sense-organs 
and the Seven Sense-functions. — All the Sense-organs originally 
Developed from the Outer Skin-covering (from the Skin-sensory 
Layer). — Organs of the Pressure Sense, the Heat Sense, the 
Sexual Sense, and the Taste Sense. — Structure of the Organ of 
Scent. — The Blind Nose-pits of Fishes. — The Nasal Furrows change 
into Nasal Canals. — Separation of the Cavities of the Nose and 
Mouth by the Palate B«of. — Structure of the Eye. — The Primary 
Eye Vesicles (Stalked Protuberances from the Twixt-brain). — 
Inversion of this Eye Vesicle by the Crystalline Lens, separated 
from the Horn-plate. — Inversion of the Vitreous Body. — The Vaa- 
oular Capsule and the Fibrous Capsule of the Eyeball. — Eyelids. 
— Structure of the Ear. — The Apparatus for Perception of Sound : 
Labyrinth and Auditory Nerve. — Origin of the Labyrinth from 
the Primitive Ear Vesicles (by Separation from the Horn-plate). — 
Conducting Apparatus of Sound : Drum Cavity, Ear Bonelets, and 
Drum Membrane. — Origin of these from the First Gill-opening 
and the Parts immediately round it (the First and Second Gill- 
arch). — Eudimentary Outer Ear, — Eudimentary Muscles of the 
Ear.shell ... ... ... ... ... ... SM 



X CONTENTS. 

CHAPTER XXII. 

DEVELOPMENT OP THE ORGANS OF MOTION. 

The Motive Apparatus of Vertebrates. — These are constituted by the 
Passive and Active Organs of Motion (Skeleton and Muaoles). — 
The Significance of the Internal Skeleton of Vertebrates. — Struo 
ture of the Vertebral Column. — Formation and Number of the 
Vertebrae. — The Ribs and Breast-bone. — Germ-history of the Verte- 
bral Column. — The Notochord. — The Primitive Vertebral Plates. — 
The Formation of the Metamera. — Cartilaginous and Bony Verte- 
bwe. — Intervertebral Discs. — Head-skeleton (Skull and Gill-arches). 
— ^Vertebral Theory of the Skull (Goethe and Oken, Huxley and 
Gegenbaur). — Primitive Skull, or Primordial Craniam. — Its Forma- 
tion from Nine or Ten Coalescent Metamera. — The Gill-arohes 
(Ribs of -the Head). — Bones of the Two Pairs of Limbs. — Deyelop- 
ment of the Five-toed Foot, adapted for Walking, from the Many- 
toed Fin of the Fish.— The Primitive Fin of the Selachians 
(Archipterygiwn of Gegenbaur). — Transition of the Pinnate into 
, the Semi-pinnate Fin. — Atrophy of the Rays or Toes of the Fins. — 
Many-fingered and Five-fingered Vertebrates. — Comparison of the 
Anterior Limbs (Pectoral Fins) and the Posterior Limbs (Ventral 
Fins). — Shoulder Girdle and Pelvis Girdle. — Germ-history of the 
Limbs. — Development of the Muscles ... .„ ... 278 

CHAPTER XXIII. 

DEVELOPMENT OF THE INTESTINAL SYSTEM. 

The Primitive Intestine of the Gastrula. — Its Homology, or Morpho- 
logical Identity in all Animals (excepting the Protozoa). — Survey 
of the Structure of the Developed Intestinal Canal in Man. — The 
Mouth-cavity. — The Throat (pharynx). — The Gullet (oesophagiis). — 
The Wind-pipe (trachea) and Lungs. — The Larynx. — The Stomach. 
— The Small Intestine. — The Liver and Gall-bladder. — The Ventral 
Salivary Gland (pancreas). — The Large Intestine. — The Rectum. —  
The First Rudiment of the Simple Intestinal Tube. — The Gastrula 
of the Amphioxus and of Mammals. — Separation of the Germ from 
the Intestinal Germ Vesicle (Gastrocystis) . — The Primitive Intes- 
tine (Protogaster) and the After Intestine (Metagaster) . — Secondary 
Formation of the Mouth and Anus from the Outer Skin. — Develop- 
ment of the Intestinal Epithelium from the Intestinal-glandnlar 
Layer, and of all other parts of the Intestine from the Intestinal- 
fibiofis Layer. — Simple Intestinal Pouch of the Lower Worms. — 



CONTENTS. n 

PASS 

Differeiitiatkm of the Primitive Intestinal Tube into a Eespiratory 
and a Digestive Intestine. — Gill-intestine and Stomach-intestine of 
the Amphioxna and Ascidian. — Origin and Significance of the Gill- 
openings. — Their Disappearance. — The Gill-arches and the Jaw- 
Skeleton. — Formation of the Teeth. — Development of the Lxmgs 
from the Swim-bladder of Fish. — Differentiation of the Stomach. — 
Development of the Liver and Pancreas. — Differentiation of the 
Small and Large Intestines. — Formation of the Cloaca ... ... 811 

CHAPTER XXIV. 

DEVELOPMENT OF THE VASCULAR SYSTEM. 

Application of the Fundamental Law of Biogeny. — The Two Sides. — 
Heredity of Conservative Organs. — Adaptation of Progressive 
Organs. — Ontogeny and Comparative Anatomy complementary of 
2ach other.— New "Theories of Evolution" of His.— The "En- 
velope Theory" and the "Waste-rag Theory." — Main Germ and 
Supplementary Germ. — Formative Yelk and Nutritive Yelk. — Phy- 
logenetic Origin of the latter from the Primitive Intestine. — Origin 
of the Vascular System from the Vascular Layer, or Intestinal- 
fibrous Layer. — Phylogenetic Significance of the Ontogenetic Suc- 
cession of the Organ-systems and Tissues. — Deviation from the 
Original Sequence ; Ontogenetic Heterochronism. — Covering Tissue. 
— Connective Tissue. — Nerve-muscle Tissue. — Vascular Tissue. — 
Relative Age of the Vascular System. — First Commencement of 
the Latter ; Coeloma. — Dorsal Vessel and Ventral Vessel of Worms. 
— Simple Heart of Ascidia. — Atrophy of the Heart in the Am- 
phioxus. — Two-chambered Heart of the Cyclostoma. — Arterial 
Arches of the Selachii. — Double Auricle in Dipneusta and Am- 
phibia. — Double Ventricle in Birds and Mammals. — Arterial Arches 
in Birds and Mammals. — Germ-history (Ontogeny) of the Human 
Heart. — Parallelism of the Tribal-history (Phy logeny) ... ... 848 

CHAPTER XXV. 

DEVELOPMENT OF THE URINARY AND SEXUAL ORGANS. 

Importance of Reproduction. — Growth. — Simplest Forms of Asemal 

Reproduction; Division and the Formation of Buds (Gemmation). — 

Simplest Forms of Sexual Reproduction : Amalgamation of Two 

Differentiated Cells ; the Male Sperm-cell and the Female Egg-cell. 

-Fertilization. — Source of Love. — Original Hermaphroditism ; 



Sft CXniTENTB. 



rA«B 



Later 8«pu»tioii of the Sezea (Gonoohorinn). — Origfxml Deyelop. 
ment of the TVo Kinds of Sexual Cells from the Two Primary 
Qerm-layers. — The Male Exoderm and Female Entoderm. — Develop, 
ment of the Testes and Ovaries. — Passage of the Sexual Cells into 
the Coelom. — Hermaphrodite Eudiment of the Embryonic Bpi- 
thelium, or Sexual Plate. — Channels of Exit, or Sexual Dnots. — 
Egg-duct and Seed-duct.— Development of these from the Primitive 
Kidney Ducts. — Excretory Organs of worms. — " Coiled Canals " of 
Binged Worms (Annelida). — Side Canals of the Arryphioxui. — 
Primitive Kidneys of the Myxinoides. — Primitive Badneys of Skulled 
Animals (Craniota). — Development of the Permanent Secondary 
Eadneys in Amniota. — Development of the Urinary Bladder from 
the Allantois. — Differentiation of the Primary and Secondary 
Primitive Kidney Ducts. — The Miillerian Duct (Egg-duct) and the 
Wolffian Duct (Seed-duct). — Change of Position of the Germ -glands 
in Mammals. — Formation of the Egg in Mammals (Graafian Fol- 
licle). — Origin of the External Sexual Organs. — Formation of the 
Gloaoa. — Hermaphroditism in Man ... ... .•• ... 388 

CHAPTER XXVI 

RESULTS OF ANTHEOPOQBNT. 

Review of the Germ-history as given. — Its Explanation by the Funda- 
mental Law of Biogeny. — Its Causal Relation to the History of the 
Tribe. — Rudimentary Organs of Man. — Dysteleology, or the Doc- 
trine of Purposelessness. — Liheritances from Apes. — Man's place in 
the Natural System of the Animal Kingdom. — Man as a Vertebrate 
and a Mammal. — Special Tribal Relation of Men and Apes. — 
Evidences regarding the Ape Question. — The Catarhina and the 
Platyrhina. — The Divine Origin of Man. — Adam and Eve. — History 
of the Evolution of the Mind. — Important Mental Differences within 
a Single Class of Animals. — The Mammalian Mind and the Insect 
Mind. — Mind in the Ant and in the Scale-louse (Cocciis). — Mind in 
Man and in Ape. — The Organ of Mental Activity : the Central 
Nervous System. — The Ontogeny and Phylogeny of the Mind. — 
The Monistic and Dualistic Theories of the Mind. — Heredity of the 
Mind. — Bearing of the Fundamental Law of Biogeny on Psychology. 
— InJBuence of Anthropogeny on the Victory of the Monistic Philo- 
sophy and the Defeat of the Dualistic. — Nature and Spirit. — Natural 
Science and Spiritual Science. — Conception of the World reformed 
by Anthropogeny ... ... ... ... ... ... 432 

N^OTSS. Remarks and References to Literature ••• ... 459 

U^DaX -.. ... ••• (•• ••• ••• 491 



LIST OF PLATES. 



Plate XII. (between p. 130 and p. 131). The Australian Mud- 
fish ((7(?rf/?ofZ?/« ^t's^eri) ... ... ... Exjilanation 

Plate XIII. (between p. 130 and p. 131). The Mexican Axolotl 
{Siredon pisciformis) and the European Land-salamander 
{Sdlamandra maculat(i) ... ... ... Explanation 

Plate Xiy. (between p. 180 and p. 181). Four Catarhines 
(Chimpanzee, Gorillas, Orang, Negro) ... Explanation 

Plate XV. (between p. 188 and p. 189). Pedigree of Man 

Explanation 



PAGE 



118 



129 



181 



184 



LIST OF WOODCUTS. 



FIQTTRE 

163. Moneron (Prof anuBba) 
164(. Bathybius, primitive slime 

165. Monemla of Mammal 

166. Cytula of Mammal . 

167. Amoeba .... 

168. Amoeboid egg-cell . • 

169. Original egg-cleavage 

170. Mulberry-germ (Morula) . 

171. Germination of Monoxenia 
172, 173. Magospbaera . 
174-179. Gastrula of various 

animals . . 

180, 181. Haliphysema . 
182, 183. Ascula of a Sponge . 
184, 185. A Gliding-worm 

(Rhabdocoelum) 

186. Acorn- worm {Balanoglos' 

8USj > a • • 

187. Appendicularia • • 

188. Asoidia . . • • 

189. AmphiozuB • . • 

190. Lamprey {Petromyxon) . 
191,192. Shark (Selachii) . 

193. Larval Salamander . 

194. Lanral Frog (Tadpole) . 



46 


wtmnm 

195, 196. Beaked AniiBal(Omt. 


PMOM 


49 
51 




thorJiAfnchus) and ita 
skeleton . ' , 


148 


61 


197. 


Pouched Animal (Marsu- 




53 
53 


198. 


pial) with young . 
Human egg-membranes . 


152 

158 


55 


199. 


Semi-ape (Lori) 


164 


65 


200. 


Human gei-m with its 




57 




membranes , 


166 


60 


201. 


Human uterus, navel-cord, 
and embryo . , 


167 


65 


202. 


Head of Nose-ape . 


175 


67 
68 


203. 
204. 


Tailed Ape (Sea-cat)' 
Skeleton of Gibbon 


175 

178 


80 


205. 
206. 


Skeleton of Orang-outang 
Skeleton of Chimpanzee . 


178 
178 




207. 


Skeleton of Gorilla . 


178 


86 


208. 


Skeleton of Man 


178 


90 


209. 


Gastrula of Gastrophy- 




90 




soma .... 


198 


91 


210. 


Germ-layers of Earth. 




103 




worms 


198 


113 

127 


211. 


Nerve-systein of Glidiag- 
worm .... 


198 


127 


212 


Human skin-ooTwrixig 


»0 



LIST OF WOODCUTS. 



nOCKB 


rA«B 


213. Epidermis oelli • 


201 


214. Tear-glands . • • 


202 


215, 216. Milk-glands . 


203 


217, 218. Central marrow of 




human embryo 


210 


219. Hnman brain • • • 


212 


220. t) »» • • • 


213 


221-223. Lyre-shaped embryo 




Chick .... 


218 


224-226. The five brain-blad- 




ders of the hnman germ 


220 


827. The fiye brain-bladders of 




Orcmiota • • . 


222 


228. Brain of Shark 


222 


229. Brain of Frog . 


222 


230. Brain of Eabbit 


224 


231. Nose of Shark 


241 


232-236. Derelopment of the 




face in embryo Chick . 


243 


237. Nose and mouth cavities . 


246 


238-240. The face in the 




human embryo • • 


247 


241. Human eye . . 


250 


242^ Development of the eyes 


253 


243. 


256 


244. Human auditory passage 


260 


246. Human auditory labyrinth 


263 


246-248. Development of the 




ecur . . . • 


264 


240. Primitive skull with ear- 




vesicles 


264 


260. Eudimentary ear-muscles 


270 


251, 252. Human skeleton 


279 


263. Human vertebral oolnmn 


280 


254. Neok-vertebra • • 


281 


265. Braast-vertebr» • • 


281 


26& LoBbAr-vertebm • • 


181 



navMM WAmm 

267. Portion of noioohOTd . 286 

258-260. Growth of the primi. 

tive vertebral series in 

embryo Chick • . 288 

261. Longitudinal aeotion of 

breast-vertebra . . 290 

262. Transverse section of same 291 

263. Intervertebral disc . . 291 

264. Human skull ... 292 

265. Head skeleton of Primi. 

tive Fish . . .296 

266. Primitive skull of Man . 297 

267. Skeleton of fin of Cera*o<iu« 302 

268. Skeleton of fin of AecM. 

thiaa . . • .302 

269. Skeleton of fin of Primi- 

tive Fish . . .302 

270. Skeleton of hand of Frog 302 

271. Skeletonof hand of Gorilla 302 

272. Skeleton of human hand . 302 

273. Skeleton of hand of Mam- 

mal .... 306 

274. Oastrula of OVynthw . 313 

275. Human stomach . • 817 

276. Gastrula of Amphioxas . 321 

277. Gastrula of Mammal . 821 
278, 279. Human germ with 

yelk-sac and allantois . 324 

280. Intestine of Tv/rhellaria . 827 

281. Intestine of Ascidia . 327 

282. Intestine of Amphioxva . 328 

283. Scales of Shark • . 832 

284. 286. Intestine of embryo 

D<^ with the intestinal 

glands .... 834 

286. Intestine with allantois . 388- 

287. latMtiJM of hamaa g«na 888 



XVI 



LIST OF WOODCUXa 



nevn 

288. Liver of humAn germ 

289. Nail-tissae . • • 

290. Intestinal epithelium 

291. Jelly-like tissue 

292. Cartilaginous tis^e 

293. Neuro-musonlar o«Ils . 
294). NerT«>tiMae • 

295. MuBole-tissne . • 

296. Yasonlar tiMua • • 

297. Blood-oelk 

298. Blood.T«««l8 of » Worm . 

299. HeiMl with blood-resselB 

of Fiflk . . • • 
300-302. Axteriai arobei 
303-306. „ w 

307-310. Developmen* of the 

hesft . . • • 
311-314. Derelopment of the 

heart • * • • 
315. Transverse section 

through Haliphjrsema . 



rAOB 


FIOUKK 


MA* 


342 


316. Rn^TUBnit at UrogmUkilia 


400 


862 


317. Primitive kidney of JBdeWo. 




862 


stoma . . .  


406 


S63 


318. Earliest primitive kidMj 




863 


rudiments 


408 


864 


319, 320. Primitive kidneyt of 




864 


Mammals 


409 


864 


821. Development of nrogoni* 




865 


tal system . 


414 


865 


822, 823. » » 


416 


371 


324-326. „ n 
827. Female sexual organs of 


416 


875 


Beaked Animal (OrrU- 




877 


thorhynehm) 


418 


878 


828. Change of position of both 
kinds of sexual glands 




380 


in human beings . 
829. Development of the human 


420 


882 


external sexual organs 


422 




380. Human egg-folliclefi 


426 


393 







LIST OF GENETIC TABLES. 



■«o*- 



TABU rAtt 

XTT. Systematic Sturey of pal»ontological periods ••• 11 
Xni. Systematic Survey of palaeontological formations ... 12 
XTV. Systematic Survey of the thickness of the forma- 
tions ... ... ... •«• ... XSr 

XV. Pedigree of Indo-Germanic languages .- ... 23 

XVI. Systematic Survey of the most important stages in 

the animal ancestral line of Man ... ... 44 

XVII. Systematic Survey of the five first stages in the 
evolution of Man (phylogenetic, ontogenetic, sys- 
tematic^ ... ... ,., ... ... 7U 

XVIII. Systematic Survey of the phylogenetic system of the 

animal kingdom ... ... ... ... 92 

XTX. Monophyletic pedigree of the a-nima.! kingdom ... 93 
XX. Systematic Survey of the phylogenetic system of 

Vertebrates... ... ... ... ... 120 

XXI. Monophyletic pedigree of Vertebrates ... ... 121 

XXn. Systematic Survey of the periods of human tribal 

history ... ... ... „. ... 184 

"y^TTI. Systematic Survey of the phylogenetic system of 

Mammals, founded on the Gastraea Theory ... 187 

XXTV. Monophyletic pedigree of Mammals ,,, m. 188 

XXV. Pedigree of Apes ... ... ... ... 189 

XXVI. Systematic Survey of the organ-systems <rf the human 

UOiXjr ••• ««• «9, ««« ••• XifV 

XXVIL Systematic Survey of the phylogenetic history of the 

human skin-covering ... ... ... 229 

XXVUL ^ Systematic Survey of the phylogenetic history of the 

human nerve-system ... ••• ••• 2S0 

34 






* • • 



Xvm LIST OF GENETIC TABLKa . 

TABLC ' 

XXIX. Systematic Survey of the ontogeny of the Bkin and 

nerve systems ... ... ... ... 232 

XXX. Systematic Survey of the phylogeny of the human 

nose ... tts ... ... ... JnSr 

XXXI. Systematic Survey of the ontogeny of the human 

eye ••• ... ... ... ... iSoo 

XXXII. Systematic Survey of the phylogeny of the humui 

ear .«• ••• ... •*• ... ^07 

XXXni. Systematic Survey of the ontogeny of the human 

t^cl*X ••« ••• ■•• ••• ••! ^00 

XXXIV. Systematic Survey of the constitution of the human 

SKeieron ... ... ... ... ... Jtio 

XXXV. Systematic Survey of the phylogeny of the human 

skeleton ... ... ... ... 309 

XXXVI. Systematic Survey of the constitution of the human 

intestinal system ... ... ... ... 330 

XXXVII. Systematic Survey of the phylogeny of the human 

intestinal system ... „. ..•. ... 346 

XXXVm. Systematic Survey of the sequence, according to 
age, of the human tissue-groups (phylogenetic 
sequence of the tissues) ... ... ... 366 

XXXTX. Systematic Survey of the sequence, according to 
age, of the human organ-systems (phylogenetic 
sequence of the organs) ... ... ,., 367 

XL. Systematic Survey of the phylogeny of the human 

vascular system ... ... ... ... 384 

XLI. Systematic Survey of the phylogeny of the human 

nearc ... ... ... ... ... ooO 

XLn. Systematic Survey of the homologies of Wormis, 
Articulated Animals {Arthropoda), Soft-bodied 
Animals (Mollusca), and Vertebrates ... ... 387 

XLm. Systematic Survey of the phylogeny of the human 

urinary and sexual organs ... ... ... 428 

XLIY. Systematic Survey of the homologies of the sexual 

organs in the two sexes of TVIammals ... •* 431 



THE EYOLUTION OF MAN 



-••»• 



CHAPTER XV. 

THE DURATION OP HUMAN TRIBAL HISTORY. 

Comparison of Ontogenetic and Phylogenetic Periods of Time. — Duration of 
Germ-history in Man and in Different Animals. — Extreme Brevity of 
the Latter in Comparison with the Immeasurable Long Periods of 
Tribal History. — Relation of this Rapid Ontogenetic Modification to the 
Slow Phylogenetic Metamorphosis. — Estimate of the Past Duration of 
the Organic World, founded on the Relative Thickness of Sedimentary 
Rock-strata, or Neptunian Formations. — The Five Main Divisions in 
the Latter : I. Primordial, or Archilithic Epoch. II. Primary, or 
Palaeolithic Epoch. III. Secondary, or Mesolithic Epoch. IV. Tertiary, 
or Caenolithic Epoch. V. Quaternary, or Anthropolithic Epoch. — The 
Relative Duration of the Five Epochs. — The Results of Comparative 
Philology as Explaining the Phylogeny of Species. — The Inter-relations 
of the Main Stems and Branches of the Indo-Germanic Languages are 
Analogous to the Inter-relations of the Main Stems and Branches of 
the Vertebrate Tribe. — The Parent Forms in both Cases are Extinct. — 
The Most Important Stages among the Human Ancestral Forms. — 
Monera originated by Spontaneous Generation. — Necessity of Sponta- 
neous Greneration. 

"In vain as yet hat it been attempted to draw an exact line of demar(»tion 
between historic and prehistoric times ; the origin of man and the period of 
his first appearance pass back into indefinable time ; the so-called archaic 
age cannot be sharply distinguished from the present age. This is the fate 
of all geological, as of all historical periods. The periods which we dis- 
iinguish are, therefore, more or less arbitrarily defined, and, like the div isious 



3 THE EVOLUTION OF MAN. 

in systematio natnral history, can only serve to bring the subject of onr 
study better before ns and to render it more manageable ; bnt not to mark 
real distinctions between different things." — Bernhard Cotta (1866). 

OuE comparative study of the Anatomy and Ontogeny of 
the Amphioxus and the Ascidian has afforded us aid, the 
value of which can hardly be over-estimated, towards 
acquiring a knowledge of human Ontogeny. For in the 
first place we have in this way filled up, as regards Anatomy, 
the wide chasm which in all previous systems of the 
animal kingdom existed between Vertebrates and Inverte- 
brates ; -and in the second place, in the germ-history of the 
Amphioxus we have recognized primordial phases of de- 
velopment, which have long disappeared from the Ontogeny 
of Man, and which have been lost in accordance with the 
law of abridged heredity. Of special importance among 
these phases of development is the Archigastrula, the ori- 
ginal, genuine Gastrula-form which the Amphioxus has 
retained up to the present time, and which re-appears in 
the same form in low invertebrate animals of the most 
diverse classes. 

The germ-history of the Amphioxus and the Ascidian 
has, therefore, so far perfected our direct knowledge of 
human genealogy, that, notwithstanding the incompleteness 
of our empiric knowledge, there is no essential gap of any 
great moment in the pedigree. We may, therefore, at once 
proceed to our task, and, aided by the ontogenetic and 
comparative-anatomical materials at our command, may 
reconstruct the main outlines of human Phylogeny. The 
immense importance of the direct application of the funda- 
mental biogenetic law of the causal connection between 
Ontogeny and Phylogeny now becomes evident. But, befort 



TntB EEQUIRED FOR THE DEVELOPMENT OF MAN. 3 

beginning this task, it -stlU be well to note a few other 
general facts which may enable us better to understand the 
phenomena we are about to study. 

Firstly, it may not be out of place to insert a few 
remarks as to the duration of time during which Man was 
developing from the animal kingdom. The first thought 
that occurs to the mind when we consider the facts in 
question, is of the immense difi'erence between the duration 
of the germ-history of Man on the one hand, and of his 
tribal history on the other. The brief period in which the 
Ontogeny of the human individual takes place, bears no 
proportion to the infinitely long period required for the 
Phylogeny of the human tribe. The human individual 
requires nine months for its perfect development from the 
fertilized egg- cell to the moment at which it is born and 
quits the mother's body. The human embryo, therefore, 
passes through the whole course of its development in the 
brief space of 40 weeks (usually in exactly 280 days). 
Each man is really older by this period than is usually 
assumed. When, for example, a child is said to be 9 J years 
old, he is in reality 10 years old. For individual existence 
does not begin at the moment of birth, but -at the 
moment of fertilization. In many other Mammals the 
duration of the embryonic development is the same as in 
Man, e.g., the Ox. In the Horse and the Ass it is somewhat 
longer, viz., from 43 to 45 weeks; in the Camel it is lo 
months. In the largest Mammals the embryo requires a 
much longer time for its complete formation within the 
maternal body; in the Rhinoceros, for instance, 1|- year, 
in the Elephant 90 weeks. In the latter case, therefore 
{cestation lasts more than twice as long as in Man — for 



4 THE EVOLUTION OF MAN. 

nearly a year and three quarters. In the smaller Mammals 
the duration of embryonic development is, on the contrary, 
much shorter. The smallest Mammals, the Harvest Mice, 
develop fully in 3 weeks ; Kabbits and Hares in 4 weeks , 
Rats and Marmots in 5 weeks ; the Dog in 9, the Pig in 17, 
the Sheep in 21, and the Stag in 36 weeks. Development is 
yet more rapid in Birds. The Chick, under normal con- 
ditions of incubation, requires only 3 weeks, or just 21 days 
for its ftiU development. The Duck, on the other hand, 
takes 25, the Turkey 27, the Peacock 31, the Swan 42, and 
the New* Holland Cassowary 65 days. The smallest of all 
Birds, the Humming-bird, quits the egg after the twelfth day. 
It is, therefore, evident that in Mammals and in Birds the 
duration of development within the egg-membranes stands 
in a definite relation to the size of body attained by each 
vertebrate species. But the latter is not the sole determin- 
ing cause of the former. There are many other circum- 
stances which influence the duration of individual develop- 
ment within the membranes of the Qgg}^^ 

In all cases, however, the duration of the Ontogeny 
appears infinitely brief when compared with the enormous, 
the infinitely long period during which the Phylogeny, or 
gradual development of the ancestral series, took place. 
This period is not to be measured by years and centuries, 
but by thousands and millions of years. Many millions of 
years must indeed have elapsed while the most perfect 
vertebrate organism, Man, gradually developed from the 
primaeval one-celled ancestral organism. The opponents of 
the development theory, who regard this gradual develop- 
ment of Man from lower animal forms, and his original 
descent from a one-celled primitive animal as incredible, 



DURATION OF HUMAN GERM-HISTOKY. 5 

do not reflect that the very same marvel actually recurs 
before our eyes in the short space of nine months during 
the embryonic development of each human individual. 
The same series of multifariously diverse forms, through 
which our brute ancestors passed in the course of many 
millions of years, has been traversed by every Man during 
the first 40 weeks of his individual existence within the 
maternal body. 

All changes in organic forms, all metamorphoses of 
animal and plant forms, appear to us all the more remark- 
able and all the more wonderful in proportion as they occur 
more rapidly. When, therefore, our opponents pronounce that 
the past development of the human race from lower animal 
forms is incredible, they must regard the embryonic develop- 
ment of the human individual from the simple egg-cell as 
far more wonderful in comparison. This latter process — the 
ontogenetic modification — which takes place before our eyes, 
must appear more wonderful than the phylogenetic modifi- 
cation, in proportion as the duration of the tribal history 
exceeds that of the germ-history. For the human embryo 
must pass through the whole process of individual develop- 
ment, from the simple cell up to the many-celled perfect 
Man, with all his organs, in the brief space of 40 weeks. On 
the other hand, we may assign many millions of years for 
the accomplishment of the analogous process of phyloge- 
netic development — the development of Man's ancestors from 
the simplest one-celled form. 

As regards these phylogenetic periods, it is impossible 
to fi^ approximately their length in hundreds or in thousands 
of years, or to establish any absolute measure of their, 
duration, liut the researches of geologists have long since 



6 THE EVOLUTION OF MAN. 

enabled us to estimate and compare the relative durations 
of the various periods of the earth's organic history. The 
most direct standard for determining the relative duration 
of geological periods is afforded by the thickness of the so- 
called Nej)tunian strata or sedimentary rock, i.e., all those 
strata which have been deposited, as mud, at the bottom 
of the ocean, or under fresh water. These stratified sedi- 
mentary rocks — limestone, clay, marl, sandstone, slate, etc. — 
which constitute the great mass of mountain-chains, and 
which are often several thousand feet in thickness, afibrd 
us data for estimating the relative lengths of the various 
periods of the earth's history. 

For the sake of completeness, I must say a few words as 
to the development of the earth as a whole, briefly indicating 
a few of the more prominent facts relating to this matter. 
At the very outset we are confronted with the weighty 
fact, that life originated on our planet at a certain definite 
period. This is a proposition that is no longer gainsaid by 
any competent geologist. We now know for certain that 
organic life upon our planet actually began at a certain 
time, and that it did not exist there from eternity, as 
some have supposed. The indisputable proofs of this are 
furnished, on the one hand, by physico-astronomical cos- 
mogeny ; on the other, by the Ontogeny of organisms. Species 
and tribes, like individuals, do not enjoy a perpetual 
life.^^"^ They also had a beginning. The time which has 
elapsed since the origin of life upon the earth up to the 
present time (and with this period of time alone we are 
here concerned) we call the " history of the organic earth," 
as distinguished from the " history of the inorganic earth " 
which embraces the period before the origin of organic life 



THE FIRST DEVELOPMENT OF ORGANIC LIFE. 7 

With regard to the latter, we first obtained clear ideas from 
the natural philosophical researches and computations of 
the great critical philosopher, Immanuel Kant, and on tliia 
point I must refer the reader to Kant's " Allgemeine Natur* 
geschicbte und Theorie des Himmels " and to the numerous 
Cosmogenies which treat the subject in a popular style. 
We cannot here dwell upon questions of this kind. 

The organic history of the earth could begin only when 
water in fluid drops existed upon its surface. For the very 
existence of all organisms, without any exception, depends 
on water in the fluid state, their bodies containing a con- 
siderable amount of the same. Our own body, in its fully 
developed state, contains in its tissues 70 per cent, of water 
and only 30 per cent, of solid matter. The amount of water 
is still greater in the body of the child, and is greatest of all 
in the embryo. In early stages of development the human 
embryo contains more than 90 per cent, of water, and not 
10 per cent, of solid matter. In low marine animals, 
especially in the Medusae, the body contains even more than 
99 per cent, of water, and not even one per cent, of solid 
matter. No organism can exist and perform its vital 
functions without water. Without water there is no life. 

Water in the fluid state, which is, therefore, in- 
dispensable for the existence of life, could not, however, 
appear upon the earth until after the temperature of the 
surface of the fiery globe had sunk to a certain point. 
Before this it existed only in the form of steam. As 
soon, however, as the first drop of water in a fluid state was 
precipitated by cooling from the envelope of steam, it began 
its geological action, and from that time to this it has 
efiected continual changes in the modification of the hard 

C7 



8 THE EVOLUTION OF MAN. 

crust of the earth. The result of this unceasing work of 
the water, which in the form of rain and hail, of snow and 
ice, of rushing torrent and surging wave crumbles and dis- 
solves the rocks, is the formation of ooze. As Huxley says, 
in his excellent "Lectures on the Causes of the Phenomena ol 
Organic Nature," the most important fact in the past history 
of our earth is ooze, and the question a^ to the history of the 
past ages of the world resolves itself into a question as to 
the formation of ooze. All the stratified rocks of our moun- 
tainous formations were originally deposited a.^ ooze at the 
bottom of the waters, and only afterwards hardened into 
solid stone. 

As has already been said, it is possible, ^y bringing 
together and comparing the various rock-strata from many 
places on the surface of the earth, to obtain an approximate 
conception of the relative ages of these various strata. 
Geologists have long agreed that there is an entirely definite 
historical sequence of the various formations. The various 
gi'oups of strata which lie one over another correspond to 
successive periods in the earth's organic history, during 
which they were deposited in the shape of mud at the 
bottom of the sea. Gradually this mud was hardened into 
solid rock. The latter, by alternate upheaval and depres- 
sion of the surface of the earth, was lifted above the water, 
and assumed the form of mountains. Four or five main 
periods in the earth's organic history, answering to the 
larger and smaller groups of these sedimentary rock-strata, 
are usually distinguished. These main periods are sub- 
divided into numerous subordinate or lesser periods. From 
twelve to fifteen of the latter are usually assumed. (Cf. 
Tables XII. and XIII, pp. H, 12.) The relative thick- 



GEOLOGICAL TIMK 9 

ness of the various groups of strata affords the means of 
approximately estimating the relative length of these various 
divisions of time. Of course we cannot say, "In a hun- 
dred years on the average a stratum of a certain thick- 
ness (say two inches) is deposited, and therefore a rock- 
stratum of a thousand feet in thickness is 600,000 
years old." For different rock-formations of equal thick- 
ness may have occupied periods of very various length 
in their deposition and consolidation. From the thickness 
of the formation we may, however, approximately judge of 
the relative length of the period during which it was 
formed. 

Of the four or five main periods of the earth's organic 
history, our acquaintance with which is indispensable for 
our Phylogeny of the human race, the first and oldest is 
known as the Primordial, Archizoic, or Archilithic Epoch. 
If we estimate the total thickness of all the sedimentary 
strata as averaging about 130,000 feet, then 70,000 feet belong 
to this first epoch — more than one half From this and other 
circumstances we may conclude that the corresponding 
Primordial or Archilithic Epoch must alone have been con- 
siderably longer than the whole long period between the 
close of the Archilithic and the present time. Probably the 
Primordial Epoch was much longer than might appear from 
the ratio of 7 : 6, which -we have given. This Epoch is divided 
into three sub-periods, known as the Laurentian, Cambrian, 
and Silurian, corresponding to the three principal groups of 
sedimentary rock-strata which constitute the Archilithic 
rocks. The enormous length of time required for the forma- 
tion at the bottom of the primordial sea of these gigantic 
strata, of over 70,000 feet in thickness, must, at all events. 



10 THE EVOLUTION OF MAN. 

have been many millions of years. During that time there 
came into existence by spontaneous generation the oldest 
and simplest organisms — those in which life began upon oui 
planet — viz., the Monera. From these, one-celled plants and 
animals first developed — the Amoebae and many kinds of 
Protista. During this same Archilithic Epoch, also, all the 
invertebrate ancestors of the human race developed from 
these one-celled organisms. We draw this conclusion from 
the fact that towards the close of the Silurian period 
a few remains of fossil Fishes are already to be found, viz., 
Selachians and Ganoids. These are, however, much more 
highly organized and of later origin than the lowest 
Vertebrates (the Amphioxus), or than the various skull-less 
Vertebrates allied to Amphioxus, which must have lived 
during this time. The latter must necessarily have been 
preceded by all the invertebrate ancestors of man. Hence 
we may characterize this entire epoch as the " age of man's 
invertebrate ancestors;" or, with special reference to the 
oldest representatives of the Vei'tebrate tribe, as the " age 
of Skull-less Animals." During the whole Archilithic Epoch 
the inhabitants of our planet consisted exclusively of 
aquatic forms ; at least, no remains of terrestrial animals 
or plants dating from this period have as yet been found. 
A few remains of land-dwelling organisms which are some- 
times referred to the Silurian Period, are Devonian. 

The Primordial Epoch was followed by the PalaeoHthic, 
Palaeozoic, or Primary Epoch, which is also separable into 
three sub-periods : the Devonian, the Carboniferous, and the 
Permian. During the Devonian Period the Old Red Sand- 
stone, or Devonian system was formed ; during the Car- 
boniferous, those great beds of coal were deposited which 



( " ) 



TABLE XII. 

Syetematio Surrey of the Palaeontological Periods, or the Gh?eat«r DiTiincaQ& 

in the History of the Organic Earth. 

I. First Epoch : The Archilithic, or Primordial Epoch, 
(Age of Stall-less Animals and Seaweed Forestg.) 

1. The Older Archilithic Epoch or Lanrentian Period 

2. The Middle Archilithic Epoch • „ Cambrian Period. 

3. The Later Archilithic Epoch „ Silurian Period. 

n. Second Epoch : The Palaeolithic, or Primary Epoch, 
(Age of Fishes and Fern Forests.) 

4. The Older Palseolithio Epoch or Devonian Period. 

5. The Middle Palaeolithic Epooh ,, Coal Period, 

^. The Later Palaeolithic Epoch ,9 Permian Period. 

m. Third Epoch : The Mesolithic, or Secondary Epoch. 
(Age of Eeptiles and Pine Forests, Coniferce.) 

7. The Older Mesolithic Epoch or Triassic Period. 

8. The Middle Mesolithic Epoch i^ Jnrassic Period. 

9. The Later Mesolithic Epoch „ Chalk Period. 

rV. Fourth Epoch : The Csenolithic, or Tertiamf Epoch, 
(Age of Mammals and Leaf Forests.) 

10. The Older Caenolithic Epoch op Eocene Period. 

11. The Middle Caenolithic Epoch ^ Miocene Period. 

12. The Later Caenolithic Epoch „ Pliocene Period. 

V. Fifth Epoch : The Anthropolithic, or Quatema/ry Epoch. 
(Age of Man and Cultivated Forests.) 

15. Tte Older Anthropolithic Epoch or loe Age, Glacial Period 
14. The Middle Anthropolithic Epoch „ Post Glacial Period. 

16. The Later Anthropolithic Epoch „ Period of Culture. 

(The Period of Culture is the Historic Period, or Period of Tradition.) 



( 12 ) 



TABLE XIII. 

Systematic Survey of the Palaeontological Formations, or the FossiliferoiiB 

Strata of the Earth's Crust. 



Boeh-Qrou^8, 



Systems. 



Formations. 



Synoruyms of 
Formutions, 



V. Quatemcmf 

Qrov/pt 

or 

Anthropolithic 

(Anthropozoic) 

groups of strata ' 

IV. Tertiary 
Qrowp,^ 
or 

Csenolithic 

(CsBnozoic) 

groups of strata 



XIV. Recent 

(Anuvinm) 
XIII. Pleistocene 
(Diluvium) 



{ 



36. Present 
35. Recent 
34. Post glacial 
33. Glacial 



XII. Pliocene ^ 32. Arvemian 



5 32. 
I 31. 



(New tertiary) \ 31. Sub-Appenlne 
XI. Miocene i 30. Falunian 

(Middle tertiary) ( 29. Limburgian 
„ -c, (28. Gypsum 

,^' J^°^,^^® , ) 27. NummuUtic 
(Old tertiary) | 26. London clay 



/iX. Cretaceous. 



III. Secondary 
' Growp, 

or 

Mesolithic 

(Mesozoic) 

groups of strata 



V 



VIII. Jura 



VII. Trias 



25. White chalk 

24. Green sand 

23. Neocomian 

22. Wealden 

21. Portlandian 

20. Oxfordian 

19. Bath 

18. Lias 

17. Keuper 

16. Muschelkalk 

15. Bunter sand 



II. Primary 

Grou'p, 

or 

Palaeoli ihic 

(Palaeozoic) 

groups of strataf 



VI. Permian f ^^ ^°^^tain 
(New red sand- J (z^'Sf^) 

' (_ 13. Red sandstone 

12. Carboniferous 



I. Primordial 

Qrowp, 

or 

Archilithic 

(Ai'chizoic) 

groups of strata 



V. Carboniferous 
(Coal) 

IV. Devonian 
(Old red sand- 
stone) 



III. Silurian 



II. Cambrian 
I. Laarentiaa 



sandstone 
11. Carboniferous 

limestone 
10. Pilton 
9. Ilfracombe 
8. Linton 

7. Indlow 
6. Wenlock 
5. Llandeilo 
4. Potsdam 
3. Longmynd 
2. Labrador 
1. Ottawa 



Upper alluvial 
Lower alluvial 
Upper diluvial 
Lower diluvial 



Upper pliocene 
Lower pliocene 
Upper miocene 
Lower miocene 
Upper eocene 
Middle eocene 
Lower eocene 

Upper cretaceous 
Middle ci'etaceous 
Lower cretaceous 
The Kentish Weald 
Upper oolite 
Middle ool'te 
Lower oolite 
Lias formation 
Upper trias 
Middle trias 
Lower trias 

Upper Permian 



Lower Permian 
Upper carbonifer- 
ous 
Lower carbonifer- 
ous 
Upper Devonian 
Middle Devonian 
Lower Devonian 

Upper Silurian 
Middle Silurian 
Lower Silurian 
Upper Cambrian 
Lower Cambrian 
Upper Lanrentian 
Lower 



GEOLOGICAL PERIODS. 1 3 

supply us with our principal fuel; in the Permian, the 
New Red Sandstone, the Magnesian Limestone (Zechstein), 
and the Cupriferous Slate were formed. The approxi- 
mate thickness of this entire group of strata is esti- 
mated at 42,000 feet at most ; some geologists make it 
Bomewhat more, others considerably less. In any case, 
this Palaeolithic Epoch, taken as a whole, is consider- 
ably shorter than the Archilithic, but yet is considerably 
longer than all the following Epochs taken together. The 
strata deposited during this Primary Epoch supply fossil 
animal remains in great abundance ; besides numerous 
species of Invertebrates we find also very many Verte- 
brates — Fishes preponderating. As early as the Devonian, 
and even during the Carboniferous and the Peimian 
Periods, there existed so great a number of Fishes, espe- 
cially Primitive Fishes (Sharks) and Ganoids, that we may 
designate the entire Palaeolithic Period as the Age of Fishes. 
The Palaeozoic Ganoids especially are represented by a 
large number of forms. 

But even during this period some Fishes began to 
accustom themselves to living upon the land, and thus gave 
rise to the Amphibian class. Even in the carboniferous 
system we find fossil remains of Amphibia — the earliest 
terrestrial and air-breathing animals. In the Permian 
Period the variety of these Amphibia becomes greater. To- 
wards its close the first Amnion-animals, the tribal ancestors 
of the true higher Vertebrate classes, seem first to appear. 
These are a few lizard-like animals, of which the Protero- 
saurus from the Cupriferous Slate at Eisenach is the best 
known. The appearance of the most ancient Amnion 
Animals (Amniota), to which the common parent-form of 



14 THE EVOLUTION OF MAN. 

Reptiles, Birds, and Mammals must have belonged, seems 
in fact to be referred by these oldest reptilian remains back 
to the ctose of the Palaeolithic Epoch. During this Epoch 
the ancestors of the human race must accordingly have 
been represented, first by true Fishes, then by Mud-Fishes 
(Bipneusta) and Amphibia, and finally by the oldest 
Amnion Animals, the Protamnia. 

After the Palaeolithic Epoch comes a third main division 
of the earth's organic history, known as the Mesolithic, or 
Secondary Epoch. This is again distinguished into three 
subdivisions — the Triassic, the Jurassic, and the Cretaceous 
Periods. The approximate thickness of the strata-groups, 
formed during these three Periods from the beginning of 
the Triassic dowti to the end of the Cretaceous Period, 
amounts in all to about 15,000 feet, not one half the thick- 
ness of the Palaeolithic deposits. During this Epoch a very 
great and varied development took place in all divisions of 
the animal kingdom. In the vei*tebrate tribe especially a 
number of new and interesting forms developed. Among 
Fishes the Osseous Fishes (Teleostei) now first appear. But 
the Reptiles surpass all others both in numbers and in 
diversity of species — the most remarkable and the most 
familiar forms being the gigantic extinct Dragons (Dino- 
saurians), the Sea-Dragons (Halisaurians), and the Flying 
Lizards (Pterosaurians). In reference to this predomiuance of 
the reptilian class this time is known as the age of reptiles. 
But the class of Birds also developed during this period, 
undoubtedly originated from a branch of the lizard-Hke 
Reptiles. This is shown by the similar embryology of Birds 
and of Reptiles, by their Comparative Anatomy, and also by 
the fact that we know of fossil birds with toothed jaws 



FAUNA OF THE GEOLOGICAL PERIODS. 1 5 

and with lizard's tail, belonging to this period (Odonr- 
tomia Archoeopteryx). Finally, it was during this period 
that there appeared upon the scene that most perfect and, 
for us, most important vertebrate class, the mammalian 
class. The oldest fossil remains of these have been found 
in the most recent Triassic strata, viz., molar teeth of 
a small insectivorous Pouched Animal (Marsupial). Numer- 
ous remains occur somewhat later in the Jura system, and 
a few in the chalk. All the remains of Mammals from this 
Mesolithic Epoch with which we are acquainted belong to 
the low Pouched Animal division ; and among these were 
undoubtedly the ancestors of Man. On the other hand, 
not a single undisputed relic has yet been discovered 
throughout all this period of one of the higher Mammals 
(Placentalia). This last division, of which Man is a member, 
did not develop till later, in the immediately subsequent 
Tertiary Epoch. 

The fourth main division of the history of the organic 
earth, the Tertiary, Csenozoic, or Csenolithic Epoch, was of 
much shorter duration than the preceding. For the strata 
deposited during this period are in all only about 8000 feet 
in thickness. This Epoch, also, is divided into three sub- 
divisions, known as the Eocene, Miocene, and Pliocene 
Periods. During these periods the most diverse develop- 
ment of the higher classes of plants and animals took place 
and the fauna and flora of our globe now approached 
nearer and nearer to their present character. The most 
highly developed class of animals, that of Mammals, now 
attained pre-eminence. This Tertiary Epoch may, therefore, 
be called the age of Mammals. The most perfect section 

of this class, the Placental Animals, among which is Man, 

35 



1 6 THE EVOLUTION OF MAN. 

now first appeared. The first appearance of Man — or to 
speak more correctly — the development of man from the 
most nearly allied ape-form, dates probably either from fhe 
Miocene or the Pliocene Period, — from the middle or the 
latest section of the Tertiary Epoch. Perhaps, as is assumed 
by others, Man strictly so-called, i.e., Man gifted with 
language, first developed from the speechless man-like Apes, 
in the subsequent Anthropolithic Age. 

At all events, the perfect development and distribution 
of the various races of Man dates from the fifth and last 
main division of the organic history of the earth, and hence 
this Epoch has been called the Anthropolithic, or Anthro- 
pozoic, and also the Quaternary Epoch. It is true that, in 
the present imperfect state of our palseontological and 
prehistoric knowledge, we cannot solve the problem as to 
whether the development of Man from the nearest allied 
Ape-forms took place in the beginning of this Anthropolithic 
Epoch, or as early as the middle or towards the close of the 
preceding Tertiary Epoch. This much, however, is certain, 
that the true development of human culture dates only 
from the Anthropolithic Epoch, and that this latter con- 
stitutes only an insignificantly small section of the entire 
enormous period of time occupied in the development of 
the organic earth. When we reflect upon this, it appears 
absurd to speak of the brief span of man's period of cu: 
ture as "the world's history." This so-called History of 
the World does not amount approximately to even one- 
half per cent, of the length of those enormous periods 
which have passed away from the beginning of the earth's 
organic history down to the present time. For this World's 



THE **AGE OF MAN." 1 7 

History, or more correctly, History of People, is itself 
only the latter half of the Anthropolithic Epoch, while 
oven the first half of this Epoch must be reckoned as a 
prehistoric period. Hence this last main period, reaching 
from the close of the Csenolithic Epoch to the present time, 
can only be called the "age of man," inasmuch as the 
diffusion and differentiation of the different species and 
races of man, which have so powerfully influenced aU the 
rest of the organic population of the globe, took place 
during' its course. 

Since the awakening of the human consciousness, 
human vanity and human arrogance have delighted in 
regarding Man as the real main-purpose and end of all 
earthly life, and as the centre of terrestrial Nature, for whose 
use and service all the activities of the rest of creation were 
from the first defined or predestined by a "wise providence." 
How utterly baseless these presumptuous anthropocentric 
conceptions are, nothing could evince more strikingly than 
a comparison of the duration of the Anthropozoic or Quater- 
nary Epoch with that of the preceding Epochs. For even 
though the Anthropolithic Epoch may embrace several hun- 
dreds of thousands of years, how small is this time when 
compared with the millions of years that have elapsed since 
the beginning of the world's organic history down to the 
first appearance of the human race ! 

K the entire duration of the organic history of the earth, 
from the generation of the first Monera down to the present 
day, is divided into a hundred equal parts, and if then, 
corresponding with the relative average thickness of the 
intervening strata-systems, the respective percentages are 



1 8 THE EVOLUTION OF MAK. 

assigned to the relative durations of the five main divisions 
or Epochs, the latter will be found to be about as follows : — 

I. Arohilithio, or archizoio (primordial) Epoch • • 68.6 

IL Palaeolithic, or palaeozoic (primary) Epoch , • 82^ 

HI. Mesolithic, or mesozoio (secondary) Epoch • • 11.6 

IT. Oasnolithic, or cenozoio (tertiary) Epoch . . • L8 

T. Attthropolithio, or anthropczoio (quaternary) Epoch . OJi 

Total ... 100.0 

The relative durations of the five main epochs of the 
earth's- organic history, are yet more clearly seen in the 
opposite Table (XIY.), in which the relative thicknesses of - 
the strata systems deposited within these Epochs is repre- 1 
sented on a scale corresponding to their actual depths. 

This table shows that the period of the so-called History 
of the World forms but an inconsiderable span in comparison I 
with the immeasurable duration of those earlier epochs during 
which Man did not exist upon this planet. Even the great 
Csenozoic Epoch, the so-called Tertiary Epoch, during which 
the Placental Animals, the higher Mammals, developed, 
includes but little more than two per cent, of the whole 
enormous duration of the organic history of the world.^^ 

And now before we turn to our proper phylogenetic 
task ; before, guided by our knowledge of ontogenetic facts 
and by the fundamental law of Biogeny, we attempt to 
trace step by step the history of the palseontological evo- 
lution of our animal ancestors, let us turn aside for a short 
time into another and apparently very different and very 
remote department of science, a general review of which 
will make the solution of the difficult problems which 
now rise belbf« na verj m«ch easier. Tke science k thai 



( 19 ) 



TABLE Xiy. 

Syitematic Snrvey of the Neptunian fossiliferous strata of the earth with 
reference to their relative sectional thickness (130,000 feet circa). 



IV. CaBnolithic Strata, 
circa 3000 feet. 


Pliocene, >^ocene, Eooen*. 


TTT. Mesolithio Strata. 


TX. Chalk System. 


Deposits of tht 




Seofmdary Epooh, cixoa 


YIIL Jnrassic System. 


U»000 feet. 


VIL Triassio System 


n. FalsBolithic Strata. 


VL Permian System. 


Deposits of the 


V. Coal System. 


Primary Epoch, oirom 




42,000 feet. 


IV. Devonian System. 




III. Silurian System, circa 


L Archilithic Strata. 


22,000 feet. 


Deposits of the 


II. Cambrian System, circa 


Anmordial Epoch, oiroa 


18,000 feet. 


70,000 feet 


I. Lam>entian System, circa 




«0,000 feet. 



20 THE EVOLUTION OF MAN. 

of Comparative Philology. Ever since Darwin, by the theory 
of Natural Selection, infused new life into Biology, and raised 
the fundamental question of development in every branch 
of science, attention has frequently and from very different 
quarters been called to the remarkable parallelism, which 
exists between the evolution of the various human lanixuages 
and the evolution of organic species. The comparison is 
quite justifiable and very instructive. Indeed it is hardly 
possible to find an analogy better adapted to throw a clear 
light on many obscure and difficult facts in the evolution of 
species; which is governed and directed by the same natural 
laws which guide the course of the evolution of language. 

All philologists who have made any progress in their 
science, now unanimously agree that all human languages 
have developed slowly and by degrees from the simplest 
rudiments. On the other hand, the strange proposition 
which till thirty years ago was defended by eminent au- 
thorities, that language is a divine gift, is now universally 
rejected, or at best defended only by theologians and by 
people whc have no conception of natural evolution. Such 
brilliant results have been attained in Comparative Philology 
that only one who is wilfully blind can fail to recognize the 
natural evolution of language. The latter is necessarily 
evident to the student of nature. For speech is a physio- 
logical function of the human organism, developing simul- 
taneously with its special organs, the larynx and the tongue, 
and simultaneously with the functions of the brain. It is, 
therefore, quite natural that in the history of the evolution 
of languages, and in their whole system, we should find the 
same correlations as in the history of the evolution of 
organic species and in their whole system. The various 



METHOD OF COMPARATIVE PHILOLOGY. 21 

larger and smaller groups of speech-forms, which are distin- 
guished in Comparative Philology as primitive languages, 
fundamental languages, parent languages, derived languages, 
dialects, patois, etc., correspond perfectly in their mode of 
development with the various larger and smaller groups of 
organisms classed in sj^stems of Zoology and Botany as 
tribes, classes, orders, families, genera, species, and varie- 
ties of the animal and vegetable kingdoms. The relations 
between these various systematic groups, or categories, aie 
in both cases identical; moreover, evolution follows the 
same course in one case as in the other. This instructive 
comparison was first elaborated by one of the most eminent 
of German philologists, one who, unfortunately, died pre- 
maturely — August Schleicher, not only a philologist but also 
a learned botanist. In his more important works, the Com- 
[)arative Anatomy and evolutionary history of languages is 
treated by the same phylogenetic method which we employ 
:n the Comparative Anatomy and evolutionary history of 
animal forms. He has especially applied this method to 
the Indo-Germanic family of languages ; and in his little 
treatise on " The Darwinian Theory and the Science of 
Language" (''Die Darwin'sche Theorie und die Sprach- 
wissenschaft "), he illustrated it by means of a synoptical 
pedigree of the Indo-Germanic family of languages.^^ 

If the formation of the various branch languages which 
have developed from the common root of the primitive 
Indo-Germanic tongue is studied with the aid of this pedi- 
gree, a' very clear idea of their Phylogeny will be acquired. 
At the same time it becomes evident how entirely analogous 
is the evolution of the greater and lesser groups of the 
Vertebrates, which have sprung from the one common root- 



22 THE EVOLUTION OF MAX. 

form of the primitive Vertebrates. The primitive Indo- 
Germanic root-tongue first separated into two chief stems ; 
the Slavo-Germanic and the Ario-Romanic main-trunks. 
The Slavo-Germanic then branched into a primitive German 
and a primitive Slavo-Lettic tongue. Similarly, the Ario- 
Romanic split up into a primitive Arian and a primitive 
Grseco-Romanic language (p. 23). If we continue our 
examination of this pedigree of the four primitive Indo- 
Germanic languages, we find that the primitive Germanic 
tongue divided into three chief branches — a Scandinavian, 
a Gothic, and a Teutonic branch. From the Teutonic branch 
proceeded, on the one hand. High German, and, on the 
other hand. Low German, to which latter belong the various 
Friesian, Saxon, and Low German dialects. Similarly, the 
Slavo-Lettic tongue developed first into a Baltic and a 
Slavonic language. From the Baltic spring the Lettic, 
Lithuanian, and Old Prussian dialects. The Slavic, on the 
other hand, give rise, in the South-east, to the Russian and 
the South Slavic dialects, and, in the West, to the Polish 
and Czech dialects. 

Turning now to the other main stem of the Indo- 
Germanic languages and its branches— the primitive Ario- 
Romanic — it is found to develop with the same luxuriance. 
The primitive Graeco-Romanic language gave rise, on the 
one hand, to the Thracian language (Albanian Greek), and 
on the other, to the Italo-Keltic. From the latter in turn 
sprung two divergent branches — in the South, the Italian 
branch (Romanic and Latin), and in the North, the Keltic, 
from which arose all the different British (Old British, Old 
Scottish, and Irish"^ and Gallic tongues. The numerous 
Iranian and Indian dialects branched out in the same way 
^m the primitive Arian language. 



( »3 ) 

TABLE XT. 

Pedigree of the Indo-Germamc Langtiagwi. 



Lithnanians Ancient Prussians 
Letts 



Anglo-Saxons 



Baltic BaoM 



Low Germans 

Netherlandere 



High Germaai 



Ancient Saxonfl 



Serbians 
Polish 
Czechs 

West Sclaves 

Bassians 
South S Clares 



South-east SolaveB 



Sclaves 



Bazong 



FriesioDB 



Low Germaos 



Boandinariana 



Goths Oemuuui 



PrimitlTe German! 



Sclavo-Letts 



Bomans 



Ancient Britinli 

Ancient Scotch 

Irish 

GhMiis 



Latins ^ 



Gktels 



Brittanese 



I 



i tm MM* 



Italians 



Eelti 



Solavo-Germani 



Italo-Eetei 



Albanese 



Greeks 



Primitive Thracittns 
Indians Iranians 




Ario-Bomaaa 



I 



I»do-Germans 



/ 



24 THE EVOLUTION OF MAN. 

A close study of this pedigree of the Indo-Germanic 
languages is, in many respects, of great interest. Com- 
parative Philology, to which we are indebted for our know- 
ledge of this subject, thus shows itself to be a true science — 
a natural science. It, indeed, long ago anticipated in its 
own province the ph^dogenetic method with the aid of 
which we now attain the highest results in Zoology and 
and in Botany. And here I cannot refrain from remarking 
how much to the advantage of our general culture it would 
be if the study of languages (which is undoubtedly one of 
the most powerful means of culture) were comparatively 
prosecuted; and if our cut and dried Philology were re- 
placed by a living, many-sided, comparative study of lan- 
guages. The latter stands in the same relation to the 
former as the living history of organic evolution does to 
the lifeless classification of species. How much deeper 
would the interest taken in the study of language by the 
students in our schools be, and how much more vivid would 
be the results if even the first elements of Comparative 
Philology were taught instead of the distasteful composi- 
tion of Latin exercises in Ciceronian style ! 

I have entered with this detail into the " Comparative 
Anatomy" and the history of the evolution of languages, 
because it is unsurpassed as a means of illustrating the 
Phylogeny of organic species. We find that in structure 
and in development these primitive languages, parent 
languages, derived languages, and dialects, correspond 
exactly like the classes, orders, genera, and species of the 
animal kingdom. The " natural system " is in both cases 
phylogenetic. Just as Comparative Anatomy, Ontogeny, and 
Palaeontology afibrd certain proof that all Vertebrates, 



MAN DESCENDED FKOM EXTINCT FORMS. 2$ 

whether extinct or extant, are descended from a common 
ancestral form, so does the comparative study of the dead 
and living Indo-Germanic language absolutely convince 
us that all these languages have sprung from a common 
origin. This monophyletic view is unanimously adopted by 
all linguists of importance who have studied the question, 
and who are capable of passing a critical judgment upon it.^^ 
The point, however, to which I would specially call your 
attention in this comparison between the various branches, 
on the one hand, of the Indo-Germanic language, and, on the 
other, of the vertebrate tribe, is that the direct descendants 
must never be confounded with the collateral lines, nor the 
extinct with the extant forms. This mistake is often 
made, and results in the formation of erroneous notions of 
which our opponents often take advantage in order to 
oppose the whole theory of descent. When, for instance, it 
is said that human beings are descended from Apes, the 
latter from Semi-apes, and the Semi-apes from Pouched 
Animals (^Marsupialia), very many people think only of the 
familiar living species of these different mammalian orders, 
such as are to be found stuffed in our museuma Now, our 
opponents attribute this erroneous view to us, and, with 
more craft than judgment, declare the thing impossible ; or 
else they ask us as a physiological experiment to transform 
a Kangaroo into a Semi-ape, this into a Gorilla, and the 
Gorilla into a Man. Their demand is as childish as the 
conception on which it is founded is erroneous ; for all 
these extant forms have varied more or less from theii 
common parent-form, and none of them are capable of pro- 
ducing the same divergent posterity which were really 
produced thousands of years ago by that parent-form.^^^ 



EVOLUTION OF MAJC. 

There is no doubt that Man is descended from an extinct 
mamTnalian form, which, if we could see it, we should 
certainly class with the Apes. It is equally certain that 
this primitive Ape in turn descended from an unknown 
Semi-ape, and the latter from an extinct Pouched Animal 
But then it is beyond a doubt that it is only in respect of 
essential internal structure, and on account of their similarity 
in the distinctive anatomical characters of the order, that all 
these extinct ancestral forms can be spoken of as members 
of the yet extant mammalian orders. In external form, in 
generic and specific characters, they must have been more or 
less — perhaps even greatly — different from all living repre- 
sentatives of the orders to which they belonged. For it 
must be accepted as a quite universal and natural fact in 
phylogenetic evolution that the parent-forms themselves, 
with their specific characters, became extinct at a more or 
less distant period. Those extant forms which come nearest 
to them, yet differ from them more or less, perhaps even 
very essentially. Hence in our phylogenetic researches 
and in our comparative view of the still living divergent 
descendants all we can undertake to do is to determine 
how far , the latter depart from the parent-form. We may 
quite confidently assume that no single older parent-form 
has reproduced itself without modification down to our time. 

We find this same state of things on comparing various 
extinct and living languages, which have sprung from one 
common primitive tongue. If, from this point of view, we 
examine the genealogical tree of the Indo-Germanic 
languages, we may conclude, on d priori grounds, that all 
the earlier primitive languages, fundamental languages, and 
ancestral languages, from which the living dialects are 



COMPARATIYE METHODS OF PHILOLOGY AND ZOOLOGY. 2^ 

descended in the first or second degree, have been extinct 
for a longer or shorter period. And this is the case. The 
Ario-Romanic and the Sclavo-Germanic tongues have long 
been altogether extinct, ^ are also the primitive Arian and 
Graeco-Romanic, the Sclavo-Lettic, and primitive Germanic 
languages. Some even of the languages descended from 
these have also long been dead, and all those of the Indo- 
Gtermanic branch which are yet extant, are akin only in 
so far as they are divergent descendants of common parent- 
forms. Some have diverged from this ancestral form more, 
others less. 

This easily demonstrable fact very well illustrates 
analogous facts in the descent of vertebrate species. Phy- 
logenetic " Comparative Philology," as a powerful ally, sup- 
ports phylogenetic " Comparative Zoology." The former can, 
however, adduce far more direct evidence than the latter, 
because the palaeontological materials of Philology, the 
ancient monuments of extinct tongues, have been far better 
preserved than the palseontological materials of Comparative 
Zoology, the fossil bones of vertebrates. The more these 
analogous conditions are considered, the more convincing 
is their force. 

We shall presently find that we can trace back the 
genealogical line of Man, not only to the lower Mammals, 
but even to the Amphibia, to the shark-like Primitive Fishes, 
and even far below these, to the skull-less Vertebrates allied 
to the Amphioxus. It must be remembered this does not 
mean that the living Amphioxus, Shark, or Amphibian accu- 
rately represent the outward appearance of the parent-forms 
of which we speak. Still less does it mean that the 
AmphioxuA, or the Shark of our day, or any extant species 



2$ THE EVOLUTION OF MAN. 

of Amphibian is an actual parent-form of the highei Vei^ 
tebrates and of Man. On the contrary, this important 
assertion must be clearly understood to mean, that the living 
forms, which have been mentioned, are side branches, which 
are much more nearly allied, and similar to the extinct 
common parent-forms, .than any other known animal forms. 
In their internal characteristic structure they remain so 
similar to the unknown parent-forms, that we should class 
them both in one order, if we had the latter before us in 
a living state. But the direct descendants of the primitive 
forms have never remained unmodified. Hence it is 
quite impossible that among the living species of animals 
we should find the actual ancestors of the human race in 
their characteristic specific forms. The essential and charac- 
teristic features, which more or less closely connect living 
forms with the extinct common parent-forms, are to be 
found in the internal structure of the body, not in the 
external specific form. The latter has been much modified 
by adaptation. The former has been more or less retained 
by heredity. 

Comparative Anatomy and Ontogeny indisputably prove 
that Man is a true Vertebrate, so that the special genealo- 
gical line of Man must of course be connected with that of 
all those Vertebrates which are descended from the same 
common root. Moreover, on many definite grounds, sup- 
plied by Comparative Anatomy and Ontogeny, we must 
assume only one common origin for all Vertebrates — 
a monophyletic descent. Indeed, if the theory of descent 
is correct, all Vertebrates, Man included, can only have 
descended from a single common parent-form — from a smgle 
primitive V^ertebrate species. The genealogical line of the 
Vertebrates, therefore, is also that of Man. 



AMCEBOID ANCESTOBS. 29 

Our tasK of ascertaining a pedigree of Man thus widens 
into the more considerable task of constructing the pedigree 
of all the Vertebrates. This is connected, as we learned from 
the Comparative Anatomy and Ontogeny of the Amphioxus 
and of the Ascidian, with the pedigree of the Invertebrate 
animals, and directly with that of the Worms, while no con- 
nection can be shown with the genealogy of the indepen- 
dent tribes of the Articulated Animals {Arthropoda), Soft- 
bodied Animals {Mollusca), and Star-animals {Echinoderma). 
As the Ascidian belongs to the Mantled Animals {Tunicata), 
and as this class can only be referred to the great Worm 
tribe, we must, aided by Comparative Anatomy and Onto- 
geny, further trace our pedigree down through various stages 
to the lowest forms of Worms. This necessarily brings us 
to the Gastrsea, that most important animal form in which 
we recognize the simplest conceivable prototype of an animal 
with two germ-layers. The Gastrsea itself must have ori- 
ginated from among those lowest of all simple animal forms, 
which are now included by the name of Primitive Animals 
[Protozoa). Among these we have already considered that 
primitive form which possesses most interest for us — the 
one-celled Amoeba, the peculiar significance of which depends 
on its resemblance to the human egg-cell. Here we have 
reached the lowest of those impregnable points, at which 
the value of our fundamental law of Biogeny is directly 
found, and at which, from the embryonic evolutionary stage, 
we can directly infer the extinct parent-form. The amoeboid 
nature of the young egg-cell, and the one-celled condition 
in which each Man begins his existence as a simple parent- 
cell or cytula-cell, justify us in affirming that the oldest 
ancestors of the human race (as of the whole animal 
kingdom) were simple amoeboid cells. 



30 THE EVOLUTION OF MAN. 

Here arises another question : " Whence, in the begin- 
ning of the organic history of the earth, at the commence- 
ment of the Laurentian period, came the earliest Amoebae ? " 
To this there is but one reply. Like all one-celled organ- 
isms, the Amoebae have originally developed only from the 
simplest organisms know to us, the Monera. These Monera, 
which we have already described, are also the simplest con- 
ceivable organisms. Their body has no definite form, and 
is but a particle of primitive slime (plasson) — a little mass 
of living albumen, performing all the essential functions of 
life, and everywhere met with as the material basis of life. 
This brings us to the last, or perhaps the first question in 
the history of evolution — the question as to the origin of 
the Monera. And this is the momentous question as to the 
prime origin of life — the question of spontaneous generation 
(generatio spontanea or cequivoca). 

We have neither time, nor indeed have we any occasion, 
to discuss at length the weighty question of spontaneous 
generation. On this subject I must refer you to my 
" History of Creation," and, especially, to the second book 
of the Gen^relle Morphologie^ and to the discussion on 
Monera and spontaneous generation in my " Studien tiber 
Moneren imd andere Protista." ^^ I have there stated 
my own views on this important subject in very great 
detail. Here I will only say a few words on the ob- 
scure question as to the first origin of life, and will answer 
it BO far as it concerns our radical conception of the 
history of organic evolution. In the definite, limited 
sense in which I maintain spontaneous generation (gene-' 
r(xUo spontanea) and assume it as a necessary h3rpo- 
thesis in explanation of the first beginning of life upon 



SPONTANEOUS GENERATIOlf. 3 J 

the earth, it merely implies the origin of Monera from 
inorganic carbon compounds. When animated bodies first 
appeared on our planet, previously without life, there must, 
in the first place, liave been formed, by a process purely 
chemical, from purely inorganic carbon combinations, that 
very complex nitrogenized carbon compound which we call 
plasson, or " primitive slime," and which is the oldest material 
substance in which all vital activities are embodied. In 
the lowest depths of the sea such homogeneous amorphous 
protoplasm probably still lives, in its simplest character, under 
the name of Bathybius.^^'^ Each individual living particle 
of this structureless mass is called a Moneron. The oldest 
Monera originated in the sea by spontaneous generation, 
just as crystals form in the matrix. This assumption, is 
required by the demand of the human understanding for 
causality. For when, on the one hand, we reflect that the 
whole inorganic history of the earth proceeds in accordance 
with mechanical laws and without any intervention by 
creative power, and when, on the other hand, we consider 
that the entire organic history of the world is also de- 
termined by similar mechanical laws ; when we see that no 
supernatural interference by a creative power is needed for 
the production of the various organisms, then it is certainly 
quite inconsistent to assume such supernatural creative 
interference for the first production of life upon our globe. 
At all events we, as investigators of nature, are bound 
at least to attempt a natural explanation. 

At present, the much agitated question of spontaneous 
generation appears very intricate, because a large number 
of very different, and in part quite absurd, conceptions are 

included imder the term "spontaneous generation," and 
r.6 



32 • THE EVOLUTION OF MAN. 

because some have supposed that the problem could be 
solved by means of the crudest experiments. The doctrine 
of spontaneous generation cannot be experimentally refuted. 
For each experiment with a negative result merely proves 
that under the conditions (always very artificial) supplied by 
us, no organism has been produced from inorganic combina- 
tions. Neither can the theory of spontaneous generation 
be experimentally proved unless great difficulties are over* 
come ; and even if in our own time Monera were produced 
daily by spontaneous generation — as is very possible — yet 
the absolute empiric proof of this fact would be extremely 
difficult — indeed, in most cases impossible. He, however, 
who does not assume a spontaneous generation of Monera, 
in the sense here indicated, to explain the first origin of life 
upon our earth, has no other resource but to believe in a 
supernatural miracle ; and this, in fact, is the questionable 
standpoint still taken by many so-called " exact naturalists," 
who thus renounce their own reason. 

Sir William Thomson has indeed tried to avoid the 
necessary hypothesis of spontaneous generation by assuming 
that the organic inhabitants of our earth originally de- 
scended from germs which proceeded from the inhabitants 
of other planets, and which, with fragments of the latter, 
with meteorites, accidentally fell on to the earth. This 
hypothesis has met with much applause, and was even 
supported by Helmholtz. Friederich Zoellner, an acute 
physicist, has, however, refuted it in his excellent natural- 
philosophical work " Ueber die Natur der Cometen," a 
critical book containing most valuable contributions to the 
history and theory of knowledge.^^'' Zoellner has plainly 
shown that the hypothesis is unscientific in two respects — 



MONERA ALONE PRODUCED BY SPONTANEOUS GENERATION. 33 

firstly, in point of logic, and secondly, in its scientific tenor 
(p. xxvi). At the same time he rightly shows that the 
hypothesis of spontaneous generation, in the sense which 
we have defined, is the " condition necessary to the conceiv- 
ability of nature in accordance with the laws of causality." 

In conclusion, I repeat, with emphasis, that it is only in 
the case of Monera — of structureless organisms without 
organs — that we can assume the hypothesis of spontaneous 
generation. Every difierentiated organism, every organism 
composed of organs, can only have originated from an 
undifferentiated lower organism by differentiation of its 
parts, and consequently by Phylogeny. Hence, even in the 
production of the simplest cell we must not assume the pro- 
cess of spontaneous generation. For even the simplest cell 
consists of at least two distinct constituent parts ; the 
inner and firmer kernel (nucleus), and the outer and 
softer cell-substance or protoplasm. These two distinct 
parts can only have come into being by differentiation of 
the homogeneous plasson of a moneron and of a cytod. It 
is for this very reason that the natural history of Monera is 
of the highest interest ; for it alone can remove the principal 
difficulties which beset the question of spontaneous genera- 
tion. The extant Monera do afford us organless and struc- 
tureless organisms, such as must have originated by spon- 
taneous generation at the first beginning of organic life 
upon the earth.^^ .  



CHAPTER XVI. 
THE ANCESTRY OF MAN. 

I. From the Moneea to the Gaste^a. 

Relation of the General Inductive Law of the Theory of Descent to tbo 

Special Deductive Laws of the Hypotheses of Descent. — Incompleteness 
of the Three Great Records of Creation : Palaeontology, Ontogeny, and 
Comparative Anatomy. — Unequal Certainty of the Various Special 
Hypotheses of Descent. — The Ancestral Line of Men in Twenty-two 
Stages : Eight Invertebrate and Fourteen Vertebrate Ancestors. — Distri- 
bution of .these Twenty-two Parent-forms in the Five Main Divisions of 
the Organic History of the Earth. — First Ancestral Stage : Monera. — 
The Structureless and Homogeneous Plasson of the Monera. — DiflFeren- 
tiation of the Plasson into Nucleus, and the Protoplasm of the Cells. — 
Cytods and Cells as Two Different Plastid-forms. — Vital Phenomena 
of Monera. — Organisms without Organs. — Second Ancestral Stage : 
Amoebae. — One-celled Primitive Animals of the Simplest and most Un- 
differentiated Nature. — The Amoeboid Egg-cells. — The Egg is Older than 
the Hen. — Third Ancestral Stage : Syn- Amoeba, Ontogenetically repro- 
duced in the Morula. — A Community of Homogeneous Amoeboid Cells. — 
Fourth Ancestral Stage : Planaea, Ontogenetically reproduced in the 
Blastula or Planula. — Fifth Ancestral Stage : Gastraea, Ontogenetically 
reproduced in the Gastrula and the Two-layered Germ-disc. — Origin of 
the Gastraea by Inversion (^invagination of the Planaea. — Haliphysema 
and Gastrophysema. — Extant Gastraeads. 

" Now, very probably, if the course of evolution proves to be so very 

simple, it will be thought that the whole matter is self-evident, and that 
research is hardly required to establish it. But the story of Columbus and 
the egg is daily repeated ; and it is necessary to perform the experiment 



INDUCTIVE AND DEDUCTIVE METHODS. 35 

lor one's self. How slowly progress is made in the knowledge eren of self- 
evident matters, especially when respectable authorities disagree, I myself 
nave experienced sufficiently." — Kael Ernst Baer (1828). 

Guided by the fundamental law of Biogeny and by the 
sure records of creation, we now turn to the interesting 
task of examining the animal parent-forms of the human 
race in their proper sequence. To ensure accuracy, we 
must first become acquainted with the various mental 
operations which we shall apply in this natural-philosophical 
research. These operations are partly of an inductive, 
partly of a deductive nature: partly conclusions from 
numerous particular experiences to a general law ; partly 
conclusions from this general law back to particular ex- 
periences. 

Tribal history as a whole is an inductive science ; for 
the whole theory of descent, as an indispensable and most 
essential part of the whole theory of evolution, is entirely 
founded on inductions. From all the biological incidents in 
plant life, in animal life, and in human life, we have derived 
the certain inductive conception that the whole of the" or- 
ganic inhabitants of our globe originated in accordance with 
one single law of evolution. To this law of evolution, La- 
marck, Darwin, and their successors gave definite form in 
the theory of descent. All the interesting phenomena ex- 
hibited by Ontogeny, Palaeontology, Comparative Anatomy, 
Dysteleology, Chorology, the (Ekology of organisms, all the 
important general laws, which we infer from multitudinous 
phenomena of these difierent sciences, and which are most 
intimately connected together, are the broad inductive 
data from which is drawn the most extensive inductive 
law of Biology, Because the innate connection betwe^i all 



36 THE EVOLUTION OF MAN. 

fchese infinitely various groups of phenomena in these dif- 
ferent departments becomes explicable and comprehensible 
solely through the theory of descent, therefore this theory 
of evolution must be regarded as an extensive inductive 
law. If we now really apply this inductive law, and with 
its help seek to discover the descent of individual organic 
species, we must necessarily form phylogenetic hypotheses, 
which are of an essentially deductive nature, and which are 
inferences from the general theory of descent back to indi- 
vidual particular cases. These special deductive conclusions 
are, however, in accordance with the inexorable laws of 
Logic, as justifiable, as necessary, and as indispensable in 
our department of knowledge as the general inductive 
conclusions of which the whole theory of evolution is 
formed. The doctrine of the animal parent-forms oi man- 
kind is also a special deductive law of this kind, which is 
the logical conclusion from the general inductive law of the 
theory of descent.^^ 

As is now very generally acknowledged, both by the 
adherents of and the opponents of the theory of descent, 
the choice, in the matter of the origin of the liuman race, 
lies between two radically different assumptions : We must 
either accustom ourselves to the idea that all the various 
species of animals and plants, Man also included, ori- 
ginated independently of each other by the supernatural 
process of a divine "creation," which as such is entirely 
removed from the sphere of scientific observation — or we 
are compelled to accept the theory of descent in its entirety, 
and trace the human race, equally with the various animal 
and plant species, from an entirely simple primaeval parent- 
form. Between these two assumptions there is no third 



FAITH OR SCIENCE. 3/ 

course. Either a blind belief in creation, or a scientific 
theory of evolution. By assuming the latter, and this is the 
only possible natural-scientific conception of the universe, 
we are enabled, with the help of Comparative Anatomy and 
Ontogeny, to recognize the human ancestral line with a 
certain approximate degree of certainty, just as is more or 
less the case with respect to all other organisms. Our 
previous study of the Comparative Anatomy and Ontogeny 
of Man, and of other Vertebrates, has made it quite clear 
that we must first seek the pedigree of mankind in that of 
the vertebrate tribe. There can be no doubt that (if the 
theory of descent is correct) Man has developed as a true 
Vertebrate, and that he originated from one and the same 
common parent-form with all other Vertebrates. This 
special deduction must be regarded as quite certain, correct- 
ness of the inductive law of the theory of descent being of 
course first granted. No single adherent of the latter can 
raise a doubt about this important deductive conclusion. 
We can, moreover, name a series of different forms of the 
vertebrate tribe, which may be safely regarded as the repre- 
sentatives of different successive phylogenetic stages of 
evolution, or as different members of the human ancestral 
line. We .can also prove with equal certainty that the 
vertebrate tribe as a whole originated from a group of low 
invertebrate animal forms ; and amono^ these we can aofain 
with more or less certainty recognize a series of members 
of the ancestral chain. 

We must, however, at once expressly say that the cer- 
tainty of the different hyi^otheses of descent, wliich are 
founded entirely on special deductive inferences, is very 
unequal Several r>^ ^hese conclusions are akeady fully 



38 THE EVOLUTION OF MAN. 

established ; others, on the contrary, are most dou]:>tful ; in 
yet others, it depends upon the subjective proportion of the 
knowledge of the naturalist and on his capability of draw- 
ing conclusions, what degree of probability he will accord 
to them. It is, at all events, necessary thoroughly to dis- 
tinguish between the absolute certainty of the general 
(inductive) theory of descent, and the relative certainty of 
the special (deductive) hypothesis of descent. We can 
never in any case prove the whole ancestral line of an- 
cestors of an organism with the same certainty with which 
we regard the theory of descent as the only scientific expla- 
nation of the organic forms. On the contrary, the special 
proof of all separate parent-forms must always remain 
more or less incomplete and hypothetical. That is quite 
natural. For all the records of creation upon which we 
tely are in a great measure incomplete, and will always 
lemain incomplete; just as in the case of Comparative 
[^hUology. 

Above all, Palaeontology, the most ancient of all records 
of creation, is in the highest degree incomplete. We know 
that all the petrifications with which we are acquainted 
form but an insignificantly small fragment of the whole 
number of animal forms and plant forms which have ever 
existed. For each extinct species obtained by us in a petrified 
condition, there are at least a hundred, probably thousands 
of extinct species which have left no trace of their existence. 
This extreme and most deplorable defectiveness of the palseon- 
tological record of creation, upon which it is impossible to 
insist too strongly, is very easily accounted for. The very 
conditions under which organic remains become petrified 
neoeesitaie it. It is also partly explicable as the result of 



INCOMPLETENESS OF THE BIOLOGICAL RECORDa 39 

an imperfect knowledge in this department. It must be 
remembered, that far the greater proportion of the rock 
strata which constitute the mountain masses of the surface 
of the earth is not yet unfolded to us. Of the coimt 
less petrifications which are hidden in the huge moun- 
tain chains of Asia and Africa, we knov/ but a few small 
samples. Part of Europe and of North America has alone 
been more minutely explored. The whole of the petri- 
factions accurately known and in our collections do not 
amount to a hundredth part of those which really exist in 
the crust of the earth. In this respect we may, therefore, 
expect a rich harvest of discoveries in the future. But, in 
spite of this, the palseontological record of creation (for 
reasons which I have amply explained in Chapter XV. of 
my "Natural History of Creation") will always remain 
extremely incomplete. 

Not less incomplete is the second, most important record 
of creation, that of Ontogeny. For the Phylogeny of the 
individual it is the most important of all. Yet, it also has 
its great defects, and often leaves us in the lurch. In this 
matter, we must distinguish quite clearly between palin- 
genetic and kenogenetic phenomena, between the original, 
inherited evolution and the later, vitiated evolution. We 
must never forget that the laws of abridged and vitiated 
heredity frequently disguise the original course of evolution 
beyond recognition. The reproduction of the Phylogeny 
in the Ontogeny is but rarely tolerably complete. The 
earliest and most important stages of germ-history are 
usually the most abridged and compressed. The youthful 
evolutionary forms have in turn often adapted themselves 
to new conditions, and have thus been modified The 



40 THE EVOLUTION OP MAN. 

struggle for existence has excited an equally strong modify- 
ing influence upon the various independent and yet un- 
developed young forms, as upon the developed and mature 
forms. Therefore, in the Ontogeny of the higher animal 
forms the Phylogeny has been very greatly limited by Keno- 
genesis ; as a rule, only a blurred and much vitiated picture 
of the original course of evolution of their ancestors now 
lies before us in the Ontogeny. Only with great precaution 
and judgment dare we infer the tribal history directly from 
the germ-history. Moreover, the germ-history itself is 
known to us only in the case of very few species. 

Lastly, the highly important record of creation afforded 
by Comparative Anatomy is unfortunately very incomplete, 
and for the simple reason, that the number of extant 
, animal species forms but a very small fragment of the 
whole number of different animal forms that have existed 
from the beginning of the organic history of the world to 
the present time. The total sum of the latter may safely 
be estimated at several millions. The number of those 
animals the organization of which has at present been 
investigated by Comparative Anatomy is very small in pro- 
portion. The more extended investigations of the future 
will, here also, open up unexpected treasures. 

In view of this evident and natural incompleteness of 
the most important records of creation, we must of course 
take good care, in the tribal history of Man, not to lay too 
great weight on single known animal forms, nor with equal 
certainty to consider all the stages of evolution which come 
under our consideration, as parent-forms. On the contrary, 
in hypothetically arranging our ancestral line, we must 
take good care to remember that the single hypothetical 



UNEQUAL VALUE OF THE *' ANCESTRAL STAGES." 4I 

parent-forms are of very diverse values in relation to the 
certainty of our knowledge. From the few remarks which, 
while speaking of the Ontogeny, we made as to the corre- 
sp&nding phylogenetic forms, it will have been understood 
that some germ-forms may with certainty be regarded as 
reproductions of corresponding parent-forms. We recog- 
nized the human egg-cell and the parent-cell which results 
from the impregnation of the latter as the first and most 
important form of this kind. 

From the weighty fact that the egg of the human being, 
like the egg of all other animals, is a simple cell, it may be 
quite certainl}^ inferred that a one-celled parent-form once 
existed, from which all the many-celled animals, Man in- 
cluded, developed. 

A second very significant germ-form, which evidently 
reproduces a primaeval parent-form, is the germ-vesicle 
(Blastula), a simple hollow sphere, the wall of which con- 
sists of a single cell-stratum. A third extremely import- 
ant form in germ-history, which may be quite safely and 
directly referred back to the tribal history, is the true Gas- 
trula. This most interesting larval form already exhibits 
the animal body composed of two germ-layers, and fur- 
nished with the fundamental primitive organ, the intestinal 
canal Now, as the same two-layered germ-condition, with 
the primitive rudiment of the intestinal canal, is common to 
all the other animal tiibes (with the single exception of the 
Primitive Animals, Protozoa), we may certainly from this 
mfer a common parent-fonn of similar construction to the 
Gastnila, the Gastrijea. Equally important in their bearing 
on the Phylogeny of Man, are the very important ontoge- 
netical form conditions which correspond to certain Worms, 



4^ THB KTOLTJTION OF MAN. 

Skull-less Animals (Acrania), Fishes, etc., etc. On the other 
hand, between these quite certain and most valuable phylo- 
genetic points, great gaps in our knowledge unfortunately 
exist, with which we shall again and again meet, and whiioh 
are satisfactorily explained by reasons which have already 
been named, especially by the incompleteness of Palaeon- 
tology, of Comparative Anatomy, and Ontogeny. 

In the first attempts to construct the human ancestral 
line, which I made in my Generelle Morphologie, and in 
the " Natural History of Creation," I arranged first ten, 
and, later, twenty-two different animal forms, which, with 
more or less certainty, may be regarded as the animal an- 
cestors of the human race, and which must be looked upon 
as in a sense the most important stages of evolution in 
the long evolutionary series from the one-celled organisms 
up to Man.^^ Of these twenty to twenty-two animal forms, 
about eight fall within the older division of the Inverte- 
brates, while twelve to fourteen belong to the more recent 
Vertebrate division. How these twenty-two most important 
parent-forms in the human ancestral line are distributed 
through the five main periods of the organic history of the 
earth, is shown in the following Table (XVI.). At least half 
of these twenty-two stages of evolution (that is, the eleven 
oldest ancestral forms) are found within the Archilithic 
Epoch, within that first main period of the organic history of 
the earth, which includes the larger half of the latter, and 
during which probably only aquatic organisms existed. The 
eleven remaining parent-forms fall within the four remaining 
main Epochs : three within the Palaeolithic Epoch, three 
within the Mesolithic Epoch, and four within the Caenolithic 
Epoch. In the last, the Anthropolithic Age, Man already 
•ziBted. 



THE TWENTY-TWO ANCESTRAL STAGES. 43 

K we would now undertake the diflBcult attempt to dis- 
covei the phylogenetic course of evolution of these twenty- 
two human ancestral stages from the very commencement of 
life, and if we venture to lift the dark veil which covers the 
oldest secrets of the organic history of the earth, we must 
undoubtedly seek the first beginning of life among those 
wonderful living beings which, under the name of Monera, we 
have already frequently pointed out as the simplest known 
organisms. They are, at the same time, the simplest 
conceivable organisms; for their entire body, in its fully 
developed and freely moving condition, consists merely 
of a small piece of structureless primitive slime or plasson, 
of a small fragment of that extraordinarily important nitro- 
genous carbon compound, which is now universally esteemed 
the most important material substratum of all the active 
phenomena of life. The experiences of the last ten years 
particularly have convinced us with more and more cer- 
tainty that wherever a natural body exhibits the active 
phenomena of life, nutrition, propagation, spontaneous 
movement, and sensation, a nitrogenous carbon compound, 
belonging to the chemical group of albuminous bodies, is 
always active, and represents the material substance through 
which these vital activities are effected. Whether, in a 
monistic sense, we conceive the function as the direct effect 
of the formed material substance, or, in a dualistic sense, we 
regard " Matter and Force " as distinct, it is at least certain 
that^ hitherto, no living organism has been observed in which 
the exercise of vital activities was not inseparably connected 
with a plasson-body. In the Monera, the simplest con- 
ceivable organisms, the whole body consists merely of plasson, 
corresponding to the "primitive slime" of earlier natural 
pthilMophy. 



( 44 ) 
TABLE XVI. 

Systematic Survey of the most Important Stages in the Animal 

Ancestral Line of Man. 

M N = Boundary between the Invertebrate and the Vertebrate Ancestors. 



Epochs of the 
Organic 

History of the 
Earth. 



Geological Periods 

of the 

Organic History 

of the Earth. 



Animal 
Ancestral Stages 

«^ 
Man. 



Nearest 
Living Relative* 
of the 
A ncestral Stages. 



L 

Archilithic 

or 

Primordial 

Epoch 



1. Lanrentian Period 
^ 2. Cambrian Period 
3. SUorian Period 



 



1. Monera 
{Monera) 

2. Oldest Amoebae 

3. Amoeboid Societies 
{Synamcebia') 

4. Ciliated planulae 

{^Plani^adrp^ 

5. Primitive Intes- 
tinal animals 
'yOastraadf^) 

6. iVimitive Worms 
(^Archelminthes') 

7. Soft- worms 
(Scolecida) 

8. Chorda animals 
(jChordonia) 

M- 

9. Skull-less animals 

(^Acrania) 
10. Round-mouths 

(^Cycloytonii) 

11. Primitive Fishes 

{^Selachii) 



I 



Bathy})iu8 

Protamoeba 

Simple Amoebae 

(Automoeba) 

Morula larvae 
Blastula larvtt 

Gastrula larvae 

Gliding Worms 
(^7\irbellaria) 
? Between the glid- 
ing worms and the 
Sea-squirts 
Sea-squirts (Ascidice] 
(Appendicularia) 

N 



Lancelets 

(Amphioxi') 

Lampreys 

{Petromyzonta') 

Sharks 

{Squalacei) 



n. 

Palaeolithic 

or 

Primary 

Epoch 



4. Devonian Period 

5. Coal Period 

6. Permian Period 



12, 



Salamander Fishes 
(^Dipneusta) 

13. Gilled Amphibia 
i^Sozobranchia) 

14. Tailed Amphibia 
jSozura) 



I 



Mud fish 

{Protoptera) 

Siren {Proteus) 

and AxolotI 

(Siredon) 
Water-newt 

(Triton) 



m. 

Mesolithic 

or 

Secondary 

Epoch 



1. Triassic Period 

8. Jurassic Period 

9. Chalk Period 



{ 



15. Primitive Am- 

niota 

{Protamnia) 

16. Primitive Mam 

mals J 

(Promammalia) ( 

17. Pouched Animals j 
(Marsupialia) \ 



? Between Tailed 
Amphibians and 
Beaked animals 

Beaked animals 
{Monotrema) 

Pouched Rate 
(Didelphyes) 



TV. 

Osnolithic 

or 

Tertiary 

Epoch 



l(V, Eocene Period 

11. Miocene Period 

12. Pliocene Period 



18. Semi-Apes ( 

(Prosimios) \ 

19. Tailed Narrow- j 

nosed Apes ) 

20. Men-like Apes or j" 
Tail-less Narrow- < 

nosed Apes. ( 

21. Speechless Men or i 
Ape-like Men ( 



Lori {Stenopa) 

Maki ( Lemur) 

Nose Apes 

Holy Apes 

Gorilla, Chimpao* 

zee, Orang, 

Gibbon 

Cretins or Micfo* 

cepbali . 



▼. 

Quaternary 
Xpooh 



u 



Diluvial Period 
AUuvlAl Period 



32. Men capaUe 
Bpeech 



"I 



Australians and 
Papoans 



MONERON AND MORULA. 45 

The soft slimeKke plasson-substance of the body of the 
Moneron is commonly called " pi^otoplasma," and identified 
with the cell-substance of ordinary animal and plant cells. 
As, however, Eduard van Beneden, in his excellent work 
upon the Gregarinae, first clearly pointed out, we must, 
strictly speaking, distinguish thoroughly between the 
plasson of cytods and the protoplasm of cells. This dis- 
tinction is of special importance in its bearing on the history 
of evolution. As was before incidentally mentioned, we 
must assume two different stages of evolution in those ele- 
mentary organisms, which, as formative particles or plastids, 
represent organic individuality of the first order. The older 
and lower stage is that of the cytods, in which the w^hole body 
consists of but one kind of albuminous substance, of the 
simplest plasson or formative material. The more recent 
and higher stage is that of cells, in which a separation or 
differentiation of the original plasson into two diff'erent 
kinds of albuminous substances, into the inner cell-kerne] 
(nucleus), and the outer cell-substance (profoplasma), has 
already taken place. 

The Monera are the simplest permanent cytods. Their 
entire body consists merely of soft, structureless plasson. 
However thoroughly we examine them with the help of 
the most delicate chemical reagents and the strongest optical 
instruments, we yet find that all the parts are completely 
homogeneous. These Monera are, therefore, in the strictest 
sense of the word, '' organisms without organs ; " or even, in 
a strictly philosophical sense, they might not even be called 
" organisms," since they possess no organs, since they are 
not composed of various particles. They can only be called 
organisms, in so far as they are capable of exercising the 



46 THE EVOLUTION OF MAN. 

organic phenomena of life, of nutrition, reproduction, sensa- 
tion, and movement. If we tried to construct, a priori, the 
simplest conceivable organism, we should always be com- 
pelled to fall back upon such a Monera. 

Although in all real Monera the body consists merely 
of such a small living piece of plasson, yet, among the 
Monera, which have been observed in the sea and in 
fresh water, we have been able to distinguish several dif- 
ferent genera and species, varying in the mode in which their 
tiny bodies move and reproduce. In the ways in which 
movement is accomplished very noticeable differences exist. 




Fig. 163. — A Moneron (Protamoeha) in the act of reprodnction : A, the 
whole Moneron, which moves, like the ordinary Amoeba, by means of variable 
processes ; B, a contraction round its circumference parts it into two halves ; 
C, the two halves separate, and each now forms an independent individual 
(much enlarged). 

In some Monera, especially in the Protamoeba (Fig. 163), 
the formless body, during its movements, invariably de- 
velops only a few, short, and blunt processes, which project 
like fingers, slowly altering their form and size^ but never 
branching. In other Monera, on the other hand {e.g., 
Protomyxa, Myxastrum), very numerous, long, fine, and 
generally thread-like processes arise from the surface of 
the movable body, and these branch irregularly, inter- 



THE BATHTBIUS. ^y 

twining their free moving ends, so as to form a net. Huge 
masses of such slime-nets crawl upon the deepest bottom 
of the sea {Bathyhius, Fig. 164). Within these soft sHme- 
like plasaon-nets slow currents continually' pass. Such a 
Moneron may be fed with finely pulverized colouring 
matter (for instance, carmine or indigo powder), if this 
powder is scattered in the drop of water under the micro- 
scope, in which the Moneron is contained. The grains 
of colouring matter at first adhere to the surface of the 
slimy body, and then gradually penetrate, and are driven 
about in irregular directions. The separate smaUest par- 
ticles, or molecules, of the Moneron-body, called "plas- 
tidules,"i86 displace each other, change their relative 
positions, and thus efiect a change in the position of the 
absorbed particles of colouring matter. This change of 
position, at the same time, proves positively that a hidden 
delicate structure does not exist. It might be argued that 
the Monera are not really structureless, but that their 
organization is so minute that, in consequence of the in- 
adequate power of our magnifying glasses, it is invisible. 
This objection is, however, invalid, for by the experiment 
of feeding, we can, at any moment, prove the entrance of 
foreign, formed, small bodies into the different parts of the 
body of the Moneron, and that these are irregularly driven 
about in all directions. At the same time we see that the 
changeable network of threads, formed by the branching 
of the protoplasmic threads and the coalescence of the con- 
fluent branches, alter their configuration every moment; 
just as has long been known to occur in the thread-nets 
of the protoplasm in the interior of the plant-cells. The 
Monera are, therefore, reaUy homogeneous and structureless; 



45 THE EVOLUTION OF MAN. 

each part of the body is every other part. Each part can 
absorb and digest nourishment ; each part is excitable and 
sensitive ; each part can move itself independently ; and 
lastly, each part is capable of reproduction and regenera- 
tion. 

The reproduction of Monera always occurs asexually. 
In the Protamoeba (Fig. 163), each individual, after it 
has grown to a certain size, simply separates into two 
pieces. Round the circumference of the body a contraction 
arises, as in cell-division. The connection between the two 
halves continually becomes more slender (B), and finally 
parts in the middle. Thus, in the simplest possible way, 
two new individuals proceed by self-division from one 
quite simple individual ((7). Other Monera, after they have 
grown to a certain size, gather themselves together into a 
spherical form. The globular protoplasmic body exudes 
a jelly-like protecting envelope, and a breaking-up of the 
whole plasson-ball takes place within this covering ; it 
breaks either into four pieces (VaTripyreUa), or into a 
large number of smaller globules {Protomonas, Protomyxa ; 
cf Plate I. in the " Natural History of Creation "). After 
a time, these globules begin to move, split the integument 
by their movement, and emerge; after which they float 
about by means of a long, thin, thread-shaped process. 
Each again passes by simple growth into the mature form. 
Thus, it is possible to distinguish different genera and 
species of Monera, on one hand, by the form of the different 
processes of the body, and, on the other hand, by the 
different kind and manner of reproduction. In the appendix 
to my monograph of the Monera I enumerated eight genera 
and sixteen species ("BioL Studien," voL i p. 182). The 



THE MONERON AND BATHYBIUS. 



49 



most remarkable of all Monera is the Bathybius, which was 
di^co veered by Huxley in 1868 (Fig. 164). This wonderful 
Muneron lives in tlie dee])est parts of the sea, especially in 




Pio. 164. — Bathybius Haeckelii (Huxley^. A Boiall piece of the formlesB 
ind continually changing plasson-net of this Moueron from the Atlantic 
f )cean . 

tlie Atlantic Ocean, and in places covers the whole floor 
of the sea in such masses, that the fine mud on the latter 
consists, in great measure, of living slime The protoplasm 
in these formless nets does not seem differentiated at 
all; each little piece is capable of forming an individual 
The active amoeboid, movements of these formless pieces of 
plasson, which were first observ^ed by the English zoologists 
Carpenter and Wyville Thomson, have recently been again 
observed by the German Arctic voyager, Emil Besaels, in 
the Bathybius of the coast of Greenland ^^ 

The origin and importance of these huge w^ww^ of 
living, formless plasson-bodies in the lowest depths of the 



50 THE EVOLUTION OF MAK. 

sea, raises many different inquiries and thoughts. Spon- 
taneous generation, especially, is naturally suggested by the 
Bathybius. We have already found that, for the origin of 
first Monera upon our globe, the assumption of spontaneous 
generation is a necessary hypothesis. We shall be all the 
more inclined to confirm it now that, in the Monera, we have 
recognized those simplest organisms, the origin of which 
by spontaneous generation, in the present condition of our 
science, no longer involves very great difficulties. For the 
Monera actually stand on the very boundary between 
organic and inorganic natural bodies.^^ 

Next* to the simple cy tod-bodies of the Monera, as the 
second ancestral stage in the human pedigree (as in that of 
all other animals), comes the simple cell, that most undifieren- 
tiated cell-form, which, at the present time, still leads an 
independent solitary life, as the Amoeba. For the first and 
oldest process of organic difierentiation, which aflfected the 
homogeneous and structureless plasson-body of the Monera, 
caused the separation of the latter into two difierent sub- 
stances ; an inner firmer substance, the kernel, or nucleus, 
and an outer, softer substance, the cell-substance, or 
protoplaama. By this extremely important separative pro- 
cess, by the difierentiation of the plasson into nucleus and 
protoplasm, the organized cell originated from the structure- 
less cytod, the nucleolated from the non-nucleolated plastid. 
That the cells which first appeared upon the earth origin- 
ated in tnis manner, by the difierentiation of the Monera, is 
a conception which in the present condition of histological 
knowledge seems quite allowable ; for we can even yet 
directly observe this oldest histological process of difier- 
entiation in Ontogeny. It will be remembered that in the 



THE MONERULA. 



51 



egg-cell of animals, either before or after fertilization, the 
original kernel disappeared. We explained this phenomenon 
as a reversion or atavism, and assumed that the egg-cell, 
in accordance "with the law of latent heredity, first fails 
back into the kernel-less, cytod stage (Fig. 165). It is only 
after fertilization is accomplished that a new cell-kernel 
arises in this cytod, which thus becomes the parent-cell 
(Cytula, Fig. 166). The transitory kemel-less cytod-con- 
dition, intermediate between the egg-celi and the parent- 
cell, is an interesting germ-form, because, in accordance 
with the fundamental law of Biogeny, it reproduces the 
origina], oldest parent-form of the Moneron; we therefore 
call it the Monerula, (Cf vol. i. pp. 178-183.) 




f Fig. 165.— Monerula of Mammal (Rabbit). The fertilized egg-cell after 
the loss or the nucleus is a simple ball of protoplasri (d). The outer covering 
of the latter is formed bj the modified zona pellucida (z) together with 
a rnucous layer (h) secreted on to the outside of the latter. In this a few 
sperm. cells are still visible ^s). 

Fig. 166.-Parent-cell (CyUda) of a Ma'_>imal (Eabbit) : k, parent, 
kernel ; n, nucleolus of the latter ; p, protoplasm of the parent-cell ; z, 
modified zona pellucida ; s, sperm-cells ; h, outer albuminous covering. 



53 THE EVOLUTION OF MAN. 

We have already explained the one-celled germ-form, 
which we see in the original egg-cell and the parent-cell 
which is originated by the fertilization of the egg-cell, aa 
the reproduction of a one-celled parent-form, to which we 
ascribed the organization of an Amoeba (cf Chap. VI.). Fcmt 
the Amoeba, as it yet lives widely distributed in the fresh 
and salt waters of the globe, must be regarded as the most 
undifferentiated and most original of the various one-celled 
Primitive Animals. As the immature primitive egg-cells 
(which as^ "primitive eggs" or Protova are found in the 
ovary of animals) are indistinguishable from ordinary 
Amoebae, we are justified in pointing to the Amoeba as the 
one-celled phylogenetic form, which, in accordance with the 
fundamental law of Biogeny, is at the present time yet 
reproduced in the ontogenetic primitive condition of the 
"Amoeboid egg-cell," As evidence of the striking cor- 
respondence of the two cells, it was incidentally men- 
tioned that in the case of some Sponges the real eggs of 
these animals were formerly described as parasitic Amoebse. 
Large one-celled Amoeba-like organisms were seen creeping 
about in the interior of the Sponge, and were mistaken for 
parasites. It was only afterwards that it was discovered 
that these "parasitic Amoebae " (Fig. 168) are really the eggs 
of the Sponge, from which the young Sponges develop. 
These egg-ceUs of the Sponge are, however, so like the 
true common Amoebae (Fig. 167) in size and structure, in 
the nature of their nuclei and in the characteristic form of 
movement of their continually changing false-feet (pseudo- 
podia), that, unless their source is known, it is impossible 
to distinguish them. 

This phylogenetic explanation of the egg-cell and its 



A^KEB^. 



53 



reference to the primseval ancestral form of the Amoeba, 
directly enables us to give a definite answer to the old hu- 
morous riddle : Which was first, the egg or the hen ? We can 





Fig. 167. — A crawling Amoeba (mucli enlarged). The whole organism has 
vthe form -value of a simple naked cell and moves about by means of change- 
able proceSses, which are extended from the protoplasmic body and again 
drawn in. In the inside is the bright-coloured, roundish cell-kernel or 
nucleus. 

Fig. 168. — Egg-cell of a Chalk-Sponge {OVynthus). The egg-cell creeps 
about in the body of the Sponge by extending variable processes, like those 
of the ordinary Amoeba. 



now very simply answer this Sphinx-question, with which 
our opponents try to shake or even to refute the Theory of 
Evolution. The egg existed much earlier than the hen. Of 
course it did not exist in the form of a bird's egg, but as an 
undifferentiated amoeboid cell of the simplest form. The 
egg existed independently during thousands of years as a 
simplest one-celled organism, as the Amoeba. It was only 
after the descendants of these one-celled Primitive Animals 
had developed into many-celled animal forms, and after 
theso had sexually difierentiated, that the egg, in the present 
physiological sense of the word, originated from the amoe- 



54 THE EVOLUTION OF MAN. 

boid cell. Even then, the egg was first a Gastrgea-egg, then 
a Worm-egg, then an Acrania-egg, then a Fish-egg, an Am- 
phibian-egg, a Reptile-egg, and lastly, a Bird-egg. The egg 
of the Bird, as it now is, is a most complex historical pro- 
duct, the result of countless processes of heredity, which 
have occurred in the course of many millions of years.^^ 

The fact that this primitive egg-form, as it first appears 
in the ovary of the most dissimilar animals, is always of 
one form, an undifferentiated cell, of the simplest amoeboid 
character, has already been pointed out as an especially 
important phenomenon. In this earliest young condition, 
immediately after the individual egg-cell has originated in 
consequence of a separation of the cells of the maternal 
ovary, no essential difference is recognizable in the egg-cells 
of the most dissimilar animals. (Cf. Fig. 10, voL i. p. 134.) It 
is not till later, when the primitive egg-cells, or the *primitive 
eggs (jprotova), have absorbed different kinds of nutritive 
yelk, and have surrounded themselves with variously fornled 
coverings, and in other ways differentiated — it is not till 
they have in this way changed into after-eggs (metova), 
that those of different classes of animals can usually be 
distinguished. These peculiarities of the developed after- 
egg, the mature egg, are naturally to be considered as only 
secondarily acquired, by adaptation to the diff^erent con- 
ditions of existence both of the egg itself and of the animal 
which forms the egg. 

The two first and oldest ancestral forms of the human 
race, which we have now considered, the Moneron and the 
Amoeba, are, considered from a morphological point of view, 
simple organisms and individuals of the first order, Plastids. 
All subsequent stages in the ancestral chain are, on the 



PRIMORDIAL EGG-CLEAVAGE. 



55 



other hand, compound organisms or individuals of higher 
order — social aggregations of a number of cells. The 
earliest of these, which, under the name of Synamoebse, 
we must rank as the third stag^ of our pedigree, are quite 
simple societies of all homogeneous undifferentiated cells ; 
amoeboid communities. To be certain as to their nature 
and origin, we need only trace the ontogenetic product of 
the parent-cell step by step. After the cytula (Fig. 166) 
has originated, by the re-formation of a cell-kernel, from 




Fig. 169. — Original or primordial egg-cleavage. The parent-cell, or 
cytula, which resulted from the fertilization of the egg-cell, first breaks up, 
by a continuous and regular process of dirisioii, into two cells (A), then into 
four (B), then into eight (C), and, lastly^ iato very numerous cleavage- 
cells (D). 

the Morula (Fig. 165), the parent-cell breaks up, by repeated 
division, into numerous cells. We have already minutely 
examined this important process of 
egg-cleavage, and have found that all 
the various modes of the latter are 
modifications of a single mode, that 
of original or primordial cleavage. 
(Cf. Chap. YIIL, p. 188.) In the Ver- 
tebrate line this palingenetic form of 
egg-cleavage has been accurately re- Fig. 170.-Muibeny. 

°° ° •^ germ, or morula. 




56 THE EVOLUTION OF MAN. 

fcained to the present time only by the Amphioxus, while 
all other Vertebrates have assumed a modified kenogenetic 
form of cleavage. (Cf. Table III., voL i. p. 241.) The latter 
certainly originated at a later period than the former, and 
the egg-cleavage of the Amphioxus is, therefore, extremely 
interesting (vol. i. p. 442). In this the parent-ceU first 
parts into two similar ceUs, the two first cleavage-cells 
(Fig. 169, A). From these, by continuous division, arise 
4, 8, 16, 32, 64 ceUs, etc., etc. (Fig. 169). The final result of 
this primordial cleavage was, we found, the formation of a 
globular mass of cells, which was entirely composed of homo- 
geneous, undifierentiated cells of the simplest characfter 
(Figs. 170, and 171, E), On account of the resemblance 
which this globular mass of cells bears to a mulberry or 
blackberry, we called it the " mulberry-germ," or morula. 

This "morula" evidently at the present day shows us 
the many-ceUed animal body in the same entirely simple 
primitive condition in which, in the earlier Laurentian 
primitive epoch, it first originated from the one-ceUed 
amoeboid primitive animal form. The morula reproduces, 
in accordance with the fundamental law of Biogeny, the 
ancestral form of the Synamoeba. For the first cell-com- 
munities, which then formed, and which laid the first 
foundation of the higher many-ceUed animal body, must 
have consisted entirely of homogeneous and quite simple 
amoeboid ceUs. The earliest Amoebae lived isolated hermit 
lives, and the amoeboid cells, which originated &om the 
division of these one-celled organisms, must also have long 
lived isolated and self-dependent lives. Gradually, however, 
by the side of these one-celled Primitive Animals, small 
amoeboid conununities arose, owing to the fact that the 



GERMINATION OF A CORAL. 




$t THE EVOLUTION OF MAN. 

Fia. 171. — Germination of a coral (Monoxenia Darwinii) : A, monerals i 
B, parent-cell (cytula) ; C, two cleavage-cells ; D, four cleavage -cells ; E, 
mulberry-germ (morula); F, vesicular germ {hlastula) ; G, vesicular germ 
in section ; H, infolded vesicular germ in section ; J, gastrola in los^tn- 
dinal section; K, gastrulay or cup-germ, seen from the outside. 



kindred cells which originated through division remained 
united. The advantages which these first cell-societies had 
in the struggle for existence over the solitary hermit cell 
must have favoured their progression, and have encouraged 
further development. Yet even at the present time several 
genera of Primitive Animals live in the sea and in fresh 
water, and permanently represent these primitive cell- 
communities in their simplest form. Such, for instance, are 
several species of Cystophrys described by Archer, the 
Rhizopods described by Richard Hertwig under the name 
of Microgromia sodalis, and the Lahyrinthulce which were 
discovered by Cienkowski ; formless masses of homogeneous 
and quite simple cells.^^ 

In order to recognize the ancestors of the human races 
which developed first phylogenetically fi^om the Syn- 
amoeba, we need only contiuue to trace the ontogenetic 
modification of th^ Amphioxus-morula in the next stages. 
The first thing noticed is that a watery fluid collects within 
the solid globular cell-mass, and the cells are forced 
together and driven out to the periphery of the body 
(Fig. 171, F.G; Plate X. Fig. 9). The soHd mulberry-germ 
thus changes into a simple hollow globe, the wall of which 
is formed of a single cell-stratum. This cell-stratum we 
called the germ-membrane (bldstoderTna), and the hollow 
globe the germ-membrane vesicle Q>lastula, or hlaato- 
sphcera). 



THE BLASTULA. 59 

The interesting blastula germ-form is also of great sig- 
nificance, for the modification of the mulberry-germ into the 
germ-membrane vesicle takes place in the same way in a 
great many animals of very dissimilar tribes ; for instance, in 
many Plant-animals and Worms, in the Ascidians, in many 
Star-animals (Echinoderma) and Soft-bodied Animals 
{Mollusca)y and also in the Amphioxus. In those animals, 
however, in the ontogeny of which there is no real palin- 
genetic blastula, this deficiency is evidently only the result 
of kenogenetic causes, of the formation of a nutritive yelk > 
and of other conditions of embryonic adaptation. We may 
therefore assume that the ontogenetic blastula is the repro- 
duction of a primaeval phylogenetic ancestral form, and that 
all animals (with the exception of the lower Primitive 
Animals) have originated from a common parent-form, the 
structure of which was essentially that of a germ-mem- 
brane vesicle. In many lower animals, the evolution of the 
blastula takes place not within the egg-coverings, but out- 
side this, free in water. Very soon after this, each cell of 
the germ-membrane begins to extend one or more movable, 
hair-like protoplasmic processes; owing to the fact that 
these cilia or whips vibrate in the water the whole body 
swims about (Fig. 171, F). This vesicular larva, the body- 
wall of which forms a cell-stratum, and which rotates and 
swims by means of the united vibrations of the cilia, has, 
ever since the year 1847, been called the planula, or ciliated 
larva. This designation, is, however, used by difierent 
zoologists in difierent senses, and the gastrula, of which we 
shall speak presently, has, especially, often been confused 
with the planula. It is, therefore, more convenient to call 
the true planula-form the blastula. 



60 



THE EVOLUTION OF MAN. 



Various kinds of Primitive Animals, which yet exist 
both in the sea and in fresh water, are formed essentially 
like the blastula, and which, in a certain sense, may be con- 
sidered as permanent or persistent blastula-forms, hoUov/ 
vesibles, the wall of which is formed of a single stratum of 
ciliated homogeneous cells. These Planseads, or Blastseads, 
as they may be called, are formed in the very mixed society 
of the Flagellatae, especially the Volvoces (for instance, 
Synura). I noticed in September, 1869, on the Island Gis-Oe, 
on the coast of Norway, another very interesting form, which 
I named- il/a^osp^OBra planula (Figs. 172, 173). The fully 
developed body of this forms a globular vesicle, the wall of 
which is composed of from thirty to forty vibratory homo* 
geneous cells, and which swims about freely in the sea. After 




Fig. 172. — The Norwegian Flimmer-ljall (MagospJicera planula), swim, 
ming by means of its vibratile fringes ; seen from tte surface. 

Fig. 173. — The same, in section. The pear-shaped cells are seen bound 
together in the centre of the gelatinous sphere by a thread-like process. 
Bech. cell contains both a kernel and a contractile vesicle. 



FLDOfEB-LABYJB. 6l 

having reached maturity the society dissolves. Each sepa- 
rate cell still lives a while independently, grows, and changes 
into a crawling Amoeba. This afterwards assumes a globu- 
lar form, and encases itself by exuding a structureless 
integument. The cell now has just the appearance of a 
common animal egg. After it has remained for a 'time in 
this quiescent state, the cell breaks up, by means of con- 
tinued division, first into 2, then into 4, 8, 16, 82 cells. 
These again arrange themselves so as to form a globular 
vesicle, put forth cilia, and bursting the encasing integu- 
ment, swim about in the same Magosphsera-form froo 
which we started. This accomplishes the entire life-history 
of this remarkable Primitive Animal.-^*^ 

K we compare these permanent blastida-forms with the 
freely swimming Flimmer-larvse or planula-condition, of 
similar structure, of many other lower animals, we may 
with certainty infer therefrom the former existence of a 
primaeval and long-extinct parent-form, the structure of 
which was essentially like that of the planula or blastula. 
We will call this the Plansea, or Blastsea. The whole body, 
in its fully developed condition, consisted of a simple hollow 
globe, filled with fluid or structureless jelly, the wall of 
which formed a single stratum of homogeneous ceUs, 
covered with cilia. Many difierent kinds and species of 
Plansea-like Primitive Animals must certainly have existed 
and formed a distinct class of Protozoa, which we may call 
Flimmer-swimmers (Planceada). A remarkable proof of the 
natural philosophical genius with which Karl Ernst Baer 
penetrated into the deepest secrets of the history of animal 
evolution, is that, as early as the year 1828 (ten years before 
the cell-theory was established), he guessed the significance 



62 THE EVOLUTION OF MAK. 

of the blastosphgera, and, truly prophetically, insisted upon 
it in his classical " Entwickelungsgeschichte der Thierc" 
(vol. L p. 223). The passage in question says : " The further 
back we go in evolution, the more do we find a corre- 
spondence in very different animals. This leads us to the 
question : Are not all animals in the beginning of their 
evolution essentially alike, and is there not a primary form 
common to all? As the germ is the undeveloped animal 
itself, it is not without reason that it is asserted that the 
simple vesicular form is the common primitive form from 
which all animals, not only ideally, but also historically, 
develop.** This latter sentence has not only ontogenetic, 
but also phylogenetic significance, and is all the more note- 
worthy because the blastula of the most diverse animals, 
and the constitution of its wall of a single ceU-stratum, was 
not then known. And yet Baer, in spite of the extreme 
deficiency of his empiric grounds, ventured the bold state- 
ment ; " At their first appearance all animals are perhaps 
alike, and are merely hollow globes." 

Next to the primaeval ancestral form of the Plansea, as 
the fifth stage in the human pedigree, is the Gastrgea, a form 
which arises from the Plansea. Of all ancestral forms this, 
as we have already shown, is of pre-eminent philosophical 
significance. Its former existence is certainly proved by the 
very important gastrula, which is met with as a transitory 
germ-stage in the ontogeny of the most various animals 
(Fig. 171, liK). We found that the gastrula, in its original, 
palingenetic form, is a globular, oval or oblong-round body, 
with one axis which has a simple cavity with one opening 
(at one pole of the axis). This is the primitive intestinal 
cavity with its mouth-opening. The intestinal wall consists 



THE GASTRSA. 65 

of two cell-sti-ata, which are, in fact, the two primary germ- 
layers, the animal skin-layer, and the vegetative intestinal 
layer. 

The ontogenetic origin of the gastmla from the blastula 
at the present day affords us trustworthy intelligence as to 
the phylogenetic origin of the Gastrsea from the Plansea. 
We found that on one side of the globular germ-membrane 
vesicle a groove-like depression begins, and this inversion 
(invaginatio) becomes continually deeper (Fig. 171, H). At 
last it is so great, that the outer, inverted part of the germ- 
membrane, or blastoderm, attaches itself closely to the inner, 
uninverted portion (Fig. 171, /). Now, if guided by this 
ontogenetic process, we wish to conceive the phylogenetic 
origin of the Gastrsea in accordance with the fundamental 
law of Biogeny, we must imagine that the one-layered cell- 
society of the globular Plansea began, especially at one point 
of its surface, to absorb nourishment. At the nutritive point 
on the surface of the ball a groove-like depression was gra- 
dually formed by natural selection. The groove, which was 
at first quite shallow, in course of time became continually 
deeper. The function of nourishing, of absorption of 
nutriment, and digestion, was soon limited to the cells 
which lined the groove, while the other ceUs undei*took the 
function of movement and covering. Thus originated the 
first division of labour among the originally homogeneous 
cells of the Planaea. 

The first result of this earliest histological difierentia- 
tion was the distinction of two difierent kinds of cells ; 
within the hollow the nutritive cells, without, on the sur- 
face, the motive or locomotive cells. The distinction of the 
two primary germ-layers was thus caused. The inner cells 

38 



04 THE EyoLunoN or man. 

of the hollow formed the inner or vegetative layer, aooom- 
plishing the functions of nutrition ; the outer cells of the 
covering formed the outer or animal layer, exercising the 
functions of locomotion and covering the body. Thia 
first and oldest process of differentiation is of such funda- 
mental significance that it deserves the deepest thought. 
When we consider that the body of the human being, 
with all its different parts, and also the body of all other 
higher animals, originates from these two simple primary 
germ-layers, we cannot over-estimate the phylogenetic 
significance of the gastrula. For in the quite simple primi- 
tive intestine, or the primitive intestinal cavity of the 
gastrula and its simple mouth-opening, the first real organ 
of the animal body, in a morphological sense, is gained; 
the earliest genuine organ, from which all the other organs 
have differentiated at a later period. The whole body of 
the gastrula is really only a " primitive intestine." 

We have already pointed out the remarkable agreement 
between the palingenetic gastrula-forms of animals of the 
most diverse classes; of Sponges (Fig. 174, A), Polyps, 
Corals (Fig. 171, /), Medusa, Worms (Fig. 175, B) Star- 
animals {Echinodermay (7), Articulated Animals {Arthro- 
poda, D), Soft-bodied Animals (Molluaca, E), and Verte- 
brates {¥), All these various forms of the palingenetic 
gastrula are much alike, and are only distinguished by such 
unessential and subordinate peculiarities, that the systematic 
zoologist, in his " natural system," could only represent them 
as different species of a single genus. The various kenoge- 
netic gastrula-forms which have been described were also 
leferable to that original palingenetic form (voL i. p. 231). The 
gastrula proved to be a germ-form common to all cIhhhoi of | 



DEVELOPMENT OF THE GASTR^A. 



65 



animals, with the exception of the Protozoa. This highly 
important fact justifies the inference in accordance with the 
fundamental law of Biogeny, that the various ancestral 




Fig. 176. 




Fig. 177. 



Pig. 178. 




Fig. 174 



Fig. 179, 



Fig. 174. — (A) Gastrnla of a Zoophyte (GastropTiysema), Haeckel. 
Fig. 175. — {B) Gustrula of a Worm (Arrow-worm, Sagitta). After Kowa- 
levsky. 

Fig. 176. — (C) GabLiuia jf au Echiuoderm (Star-fish, TJraster). After 
Alexander Agassiz. 

Fig. 177. — (D) Gustrula of an Arthropod (Primitive Crab, Nauplius). 

Fig. 178.— (E) Gastrnla of a Mollusc (Pond-snail, Limnoeus). After , 
Karl Rabl. 

Pig. I79,_(2r') Gastrnla of a Vertebrate (Lancelot, Amphioxus) After 
Kowalevsky. 



66 THE EVOLUTION OF MAN. 

lines of all these classes of animals have developed phylo- 
genetically from the same parent-form. This most signifi- 
cant primaeval parent-form is the Gastraea. 

The Gastrea was at any rate already present in the 
sea during the Laurentian period, and by means of its 
vibratory fringe hurried about in the water, just like the 
yet extant free-moving ciliated gastrulae of this age. Pro- 
bably the primaeval Gastraea, which has been extinct for 
many millions of years, differed from the living gastrula 
of the present day only in some unessential point. On 
grounds derived from Comparative Anatomy and Ontogeny, 
the explanation of which would lead us too far, we may 
assume that the Gastraea had already acquired sexual re- 
production, and did not only propagate its species asexually 
(by division — ^bud-formation or spore-formation), as was 
probably the case with the four preceding ancestral stages. 
Presumably, single cells of the primary germ-layers as- 
sumed the character of egg-cells, others that of fertilizing 
seed-cells. (Cf Chapter XXV.) This hypothesis is founded 
on the fact that sexual reproduction is yet met with in the 
same simple forms in the lowest Plant- Animals (Zoophyta), 
especially in the Sponges. 

Two small animal forms are especially interesting in 
their bearing on this aspect of the Gastraea theory. They 
have as yet been little observed, but of all extant animals 
they are most nearly allied to the primaeval .Gastraea, and 
may therefore be called "the Gastraeads of the present 
day." ^^ One of these animals, Haliphysema (Figs 180 and 
181), has been described by Bowerbank as a Sponge ; the 
other, Gastrophysema, by Carter as a Rhizopod (as " Squa- 
mulina "). The entire mature body of the developed person 



EXTANT GASTRJilADS. 



67 



of Haliphysema forms a most simple, cylindrical or egg- 
shaped pouch, the wall of which consists of two cell-strata. 
The cavity of the pouch is the stomach-cavity, and the 





Pigs. 180, 181. — Haliphijsema primordiale, an extant Gastrsea-form. 
Fig. 180. External view of the whole spindle-shaped animal (attached by 
its foot to seaweed). Fig. 181. Longitudinal section of the same. The 
primitive intestine (d) opens at its upper end in the primitive mouth (m). 
between the whip-cells (g) lie amoeboid eggs (e). The skin-layer Qi) below 
is encrusted with grains of sand, above with sponge-spicnles. 



opening at the top is the mouth-opening (Fig. 181, m). 
The two cell-strata forming the wall of the pouch are the 



68 THE EVOLUTION OF MAN. 

two primary germ-layers. These most simple Plant- Animals 
differ from the gastriila principally in the fact that the 
former are attached by one end (that opposite to the mouth- 
opening) to the bottom of the sea, while the latter are 
free. Moreover, the cells of the skin-layer are coalescent and 
have included many foreign bodies, such as sponge-spicules, 
sand-grains, etc., which serve to support the body-wall 
(Fig. 180). The intestinal layer, on the other hand, con- 
sists merely of a stratum of ciliated cells (Fig 181, d). 
When the Haliphysema is sexually mature, individual cells 
of its entoderm assume the character of female egg-cells; 
on the other hand, individual cells of its exoderm become 
male seed-cells ; the fertilization of the former by the latter 




Figs. 182, 183.— Ascnla of a Sponge (Olynthus). Fig. 182, from the ont- 
side ; Fig. 18.S, in longitudinal section : g, primitive intestine ; o, primitive 
mouth ; i, intestinal layer ; e, Bkin-layer. 



BSFBODXTCnON IN THE OASTR^ADS. 69 

takes place directly through the stomach-cavity. A true 
palingenetic gastrula (Fig. 174) develops, just as in the 
Monoxenia (Fig. 171), from the fertilized egg. This swims 
about for a time in the sea, then attaches itself, and in this 
state resembles a simple young-form, which occurs in the 
course of the evolution of many other Plant- Animals, and 
which is called the ascula (Figs. 182, 183). In consequence 
of the absorption of foreign bodies by the exoderm, it 
becomes the Halipkysema. 

When we consider that there is no other important 
difference between the free-swimming gastrula and this 
attached, simplest Plant-animal, we are fairly justified in 
stating that in the simplest form of Gastraea sexual repror 
duction must have taken place in the same way. In the 
Grastrseads, just as in Plant-animals, both kinds of sexual 
cells — egg-cells and sperm-cells — must have formed in the 
same person; the oldest Gastrseads must, therefore, have 
been hermaphrodite. For Comparative Anatomy shows 
that hermaphroditism, that is, the union of both kinds of 
sexual ceUs in one individual, is the oldest and original con- 
dition of sexual differentiation ; the separation of the sexes 
{Gonochorismus) did not originate till a later period. 



( 70 ) 



TABLE XTII. 

Systomatio Snryey of the five earliest evolutionary stages of the Haman Aiii 
oestral Line, compared with the five earliest stages of Individual and 
of Systematic Evolution. 



Form-Value 

Of the five earliest 
Rtagea of the animal 
bo47. 



1. 

Firtt Stage. 

A quite simple cjtod 
(a non*nacleated plas- 
tid). 



8«eond Sttige, 

A. simple cell (• 
Ducleated plastid). 



Third Stage. 

A qnite simple ag- 
gregation of simple, 
similar oella.. 



1 



Fourth Stage. 

A simple boUow globe, 
filled with liquid, the 
wall of which consists 
of a single stratum of 
bomogeneeuB cells. 



Fifth Stage. 

A hollow body, with 
a single axis, the wall 
»f which consists of 
different cell-strata ; 
with an opening at one 
pole of Um 



Phylogeny. 

The five earliest 
stages in the evolu- 
tion of the tribe. 



1. 

Monera. 

The oldest animal 
Monera (originating 
by spontaneous gene- 
ration). 



2. 

Amoeba. 
Oldest animal Amoeba. 



3. 

Synamoeba. 

The oldest aggrega- 
tion of animal AmoelMe. 



4. 

Flansea. 

An animal hollow 
globe, the wall of 
which consists of a 
single stratum of 
ciliated cells. 
(piaitcBO.') 



5. 

Gastrsea. 

Parent-form of In- 
testinal animals, or 
Mftazoa. Simple pri- 
mitive intestine with 
primitive mouth. The 
body-wall is formed 
by the exoderm and 
the entoderm. 



Ontogeny. 

The five earliest 
stages in the evolu- 
tion of the germ. 



1. 

Monerala. 

A non - nucleated 

animal-egg (after fer- 

and after 

the 



tilization 
loss of 
vesiele). 



germ- 



I 

2. 

Cytnla. 

A nucleated, ferti- 
lized animal-egg (" first 
cleavage globule "). 



3. 

Morula. 

•• Mulberry-germ." 
A globular mass of 
cleavage-cells. 



4. 

Blastnla. 

A hollow globe, the 
wall of which consists 
of a single stratum 
of homogeneous cells 
(the Planula of lower 
animals). 

(blastosptuera.) 



5. 

Oastmla. 

Intestinal larva. 

A simple intestinal 
cavity with a mouth- 
opening. The body- 
wall is formed by the 
two primary germ- 
layers. 



The System. 

The five earliest 
stages in the animal 
system. 



1. 

Monera. 

Protamoeba, Bathy- 
bius, and other extant 
Monera. 



2. 

Amoeba. 

Extant Amoiba. 



L^byrinthnla. 

A mass of similar, 
one - celled primitive 
animals. 



4. 

Magosphaera. 

A hollow globe, the 
wall of which consists 
of a single stratum of 
homogeneous ciliated 
cells. 



5. 

Ealiphysema. 

A quite simple plant- 
animal. An unarticu- 
lated uniaxial person, 
the body-wall of which 
consists of the exoderm 
and the entoderm. 



, CHAPTER XVIL 
THE ANCESTRAL SERIES OF MAN. 

II. Feom the Primitive Woem to the Skulled Animal. 

rhe Foar Higher Animal 'Jribes are descended from the Worm Tribe. — Tlu 
Descendants of the Gastraea ; in one direction the Parent Form of Plant- 
Animals (Sponges and Sea-Nettles), in the other the Parent Form of 
Worms. — Radiate form of the former, Bilateral form of the latter. — The 
Two Main Divisions of the Worms, Accelomi and Coelomati : the former 
without, the latter with, a Body Cavity and Blood vessel System. — 
Sixth Ancestral Stage : Archelminthes, most nearly allied to Turbellaria. 
— Descent of the Coelomati from the Accelomi. — Mantled Animals 
{Tunicata) and Chorda- Animals (Chordoma). — Seventh Stage: Soft- 
Worms (Scolecida). — A Side Branch of the latter: the Acorn- Worm 
{Balanoglossus). — Differentiation of the Intestinal Tube into Gill-intes- 
tine and Stomach-intestine. — Eighth Stage : Chorda- Animals (Chor- 
donia). — Ascidian Larva exhibits the Outline of a Chorda- Animal. — 
Construction of the Notochord. — Mantled Animals and Vertebrates as 
Diverging Branches of Chorda- Animals. — Separation of Vertebrates from 
the other Higher Animal Tribes (Articulated Animals, Star-Animals, 
Soft-bodied Animals). — Significance of the Metameric Formation. — 
Skull-less Animals (Acrania) and Skulled Animals (Cro/niota). — Ninth 
Ancestral fetage : Skull-less Animals. — Amphioxus and Primitive Verte- 
brate. — Development of Skulled Animals (Construction of the Head, 
Skull, and Brain). — Tenth Ancestral Stage : Skulled Animals, allied 
to the Cyclostomi (Myzinoidoe and PetromyzonidcB). 

" Not like the gods am I ! Full well I know | 
But like the worm which in the dust must go, 
And, finding in the dust his life and weal, 
Is crashed and buried by the traveller's heel.— 



79 THB EYOLUnON OF MAN. 

Wlij do«t tlion grin at me, thou hollow sknll f 

As though of old thy brain, like mine, was Tezed, 

Had looked to find bright day, but in the twilight dvll. 
In Maroh for truth, was sad and sore perplexed ! " 

Both in prose and in poetry man is very often compared 
to a worm. " A miserable worm," " a poor worm," are 
common and almost compassionate phrases. If we cannot 
detect any deep phylogenetic reference in this zoological 
metaphor, we might at least safely assert that it contains 
an unconscious comparison with a low condition of animal 
developmetit which is interesting in its bearing on the 
pedigree of the human race. For there is no doubt that 
the vertebrate tribe, in common with those of the other 
higher classes of animals, have developed phylogenetically 
from that multiform group of lower invertebrate animals 
which are now called Worms. However closely we limit 
the zoological significance of the word " Worm," it yet 
remains indubitable that a large number of extinct Worms 
must be reckoned among the direct ancestors of the human 
race. 

The group of Worms (VerTnes) is much more limited in 
the Zoology of the present day, than was the same class in 
the older Zoology, which followed the system of Linnaeus. 
It, however, yet includes a great number of very diverse 
lower animals, which, phylogenetically, we may regard as 
the few last living twigs of an immense spreading tree, 
the trunk and main branches of which have for the most 
part long since died oft*. On the one side, among the 
widely divergent classes of Worms, are found the parent- 
formB of the four higher tribes of animals, the Molluscs, 
Star-animals, Articulates, and Vertebrates ; on the other side, 



DEYILOPMENT OF WORMS AND PLANT-ANIMAIA f$ 

several comprehensive groups and also single isolated genera 
of Worms are to be regarded as root-suckers which have 
sprouted directly from the rest of the primaeval family-tree 
of the Worms. Some of these suckers have evidently 
changed but little from the long-extinct parent-form, the 
Primitive Worm (Prothelmis), which is immediately con- 
nected with the Gastrsea. 

Comparative Anatomy and Ontogeny clearly and sig- 
nificantly prove that the Gastra3a must be regarded a^ 
the direct ancestor of this Primitive Worm. Even now, a 
gastrula develops from the egg of all Worms after its 
cleavage. The lowest and most imperfect Worms retain 
throughout life an organization so simple that they are but 
little raised above the lowest Plant-animals, which are also 
immediate descendants of the Gastraea, and which also yet 
develop directly from the gastrula. K the genealogical 
relation of these two lower animal tribes, the Worms and 
the Plant-animals, is closely examined, it becomes evident 
that the most probable hypothesis of their descent is, that 
the two originated, as independent branches, directly from 
the Gastraea. On the one side, the common parent-form of 
the Worms developed from the Gastraea ; as, on the other 
side, did the common parent-form of the Plant-animals. 
(Of Tables XVIII. and XIX.) 

The tribe of Plant-animals (Zoophytes, or Ccdenterata) 
now comprehends, on the one side, the main class of Sponges 
(Spongice) ; on the other, the main class of the Sea-nettles 
(Acalephce); to the former belong the Gastraeads and 
Poriferae, to the latter the Hydroid^polyps, the Medusae, 
Ctenophorae, and Corals. From the Comparative Anatomy 
and the Ontogeny of these we may infer, with great pro- 



74 THE EVOLUTION OF MAK. 

bability, that all these Plant-animals descend from a 
common and very simple parent-form, the structure of 
which resembled that of the ascula in essential points 
(Figs. 182, 183, p. 68). The uniaxial outline of the ascula 
and the gastrula is usually retained by the Sponges, while 
in most Sea-nettles (Accdephce) transverse axes have been 
differentiated in the course of further evolution, thus giving 
rise to a characteristic radiate structure with a pyramidal 
general outline. 

In distinction from this predominant radiate outline of 
Plant-animals, a marked bilateral general outline is de- 
veloped from the first in the second offshoot from the 
gastrula, in the Worms. As the radiate form is marked by 
adaptation to an adherent mode of life, so is the bilateral 
form by adaptation to certain definite acts of free loco- 
motion. The constant direction and carriage of the body 
which would be maintained in this mode of free locomotion, 
conditioned the two-sided, or bilateral outline of the 
symmetrical Worms. Even the parent-form of the latteu, 
the Primitive Worm (Prothelmis) must have acquired this 
character, and thus have become distinguished from the 
uniaxial parent-form of the Plant-animals. In this simple 
mechanical impetus, in the defined free locomotion of the 
Worms, on the one hand, and in the stationary mode of 
life of the earliest Plant-animals on the other, we must look 
for the efficient cause which produced in the one the bi- 
lateral or two-sided, in the other the radiate outUne of the 
body. The former, the bilateral outline, has been inherited 
by the human race from the Worms. 

Except through the Gastrsea, the common parent-form 
of Plant-animals and Worms, the human race is, therefore, 



THE WORMS AS ANCESTORS OF MAH. 75 

not related to the Plant-animals. It will be our next task 
to consider more closely the pedigree of Man in so far as 
it coincides with that of the Worms. Let us examine how 
far the Comparative Anatomy and Ontogeny of Worms 
justify us in looking among the latter for primaeval ancestors 
of Vertebrates, and therefore of Man. For this end we must 
first consider the zoological system of Worms. In accord- 
ance with the most recent investigations of the Comparative 
Anatomy and Ontogeny of Worms, we divide (without 
reference to the many and various peculiarities of the 
numerous separate classes, which in this place do not 
interest us) the whole mass of forms within this tribe 
into two large main groups. The first main group, which 
we call Bloodless Worms (Acoelomi), comprehends the 
earlier division of the lower Worms, which have no true 
body-cavity, no system of blood-vessels, no heart, no blood, 
— in short, none of the parts connected with this organ- 
system. The second main gi'oup, on the contrary, called 
Blood- worms (Coelomati), are distinguished from the former 
by the possession of a true body-cavity, and also by the 
presence of a blood -like fluid, which fills this cavity ; 
most of them also develop special blood-vessels, which 
again cause further correlated advances in structure. The 
relation of these two main groups of Worms is very evi- 
dently phylogenetic. The Acoelomi, which are very nearly 
allied to the Gastrsea and the Plant-animals, are to be 
regarded as an earlier and lower group, from which the 
more recent and higher division of the Coelomati developed, 
perhaps towards the end of the Laurentian Period. 

We will first carefully examine the lower group otf 
Worms, the Acoelomi, among which we must look for tlM 



76 THE EVOLUTION OF MAN. 

sixth ancestral stage of the human race, the stage imme 
diately following the gastrula. The name "Acoelomi ' 
signifies " Worms without a body-cavity, or coeloma," and 
therefore without blood, or vascular system. The extant 
Acoelomi are generally included in a single class, which, on 
account of their flattened bodies, are called Flat-worms 
{Plathelminthes). To this class belong the Gliding- worms 
(TurbeUaria), which live independently in the water; also 
the parasitic intestinal Sucking-worms (Trematoda), and 
the Tape- worms (Cestoda), which have become yet more 
degraded *by parasitism. The phylogenetic relations of the 
three forms of Flat- worms are very evident ; the Sucking- 
worms originated from the free Gliding- worms by adaptation 
to a parasitic mode of life ; and, by a yet more completely 
parasitic life, the Tape-worms originated from the Sucking- 
worms. These are striking examples of the gradually 
increasing degeneration of the most important organs. 

In addition to these well-known extant Flat- worms, 
great numbers of other Acoelomi must have lived during 
the Archilithic ^poch, which in general form were very 
much like those of the present day, but were, in some 
respects, yet more simply organized, and were, in their 
lowest stages of development, immediately connected with 
the Gastraeads. The whole of these lowest Acoelomi, among 
which the common parent-form of the whole Worm tribe 
(the Prothelmis) must have been, may be classed as " Primi- 
tive Worms " (Archelminthes). 

The two classes of the Acoelomi, the Primitive Wo^m^ 
and the Flat-worms, represent in their externa) form the 
simplest bilateral condition of the animal body. The 
body is a simple oval, usually somewhat flattened, with- 



BLOODLESS WOBMa 77 

oufc any appendage (Figs. 184, 185). The dorsal side of 
the leaf-like body differs from the ventral side, on which 
the Worm creeps. Accordingly, even in these most simple 
Worms there are the three definite axes which mark the 
bilateral type-form, and which re-occur in the human 
body and in that of all higher animals : (1) a longitudinal 
axis (main axis), which passes from front to rear; (2) 
a lateral axis, passing from right to left ; and (3) a 
sagittal axis, passing from the dorsal to the ventral surface. 
(C£ vol. i. p. 257.) This so-called symmetrical or " bilateral" 
arrangement of the outline of the body is simply the 
mechanical result of adaptation to a creeping form of loco- 
motion, during which one end of the body is always directed 
forwards. The geometric outline of the gastrula, as of the 
ajscula, has but one axis with imequal poles {Monaxonia 
diplopola). The typical outline of Worms, as of Vertebrates, 
is, on the contrary, bilateral, with tranverse axes (Stau- 
raxonia dipleura)}^ 

The whole outer surface of the Gliding-worms (Turhel- 
laria) is covered, as in the gastrula, with a thick, fine 
ciliated coat ; that is, with a fur-like covering of extremely 
fine and close microscopic hairs, which are direct processes 
of the uppermost cells of the epidermis, and maintain an 
uninterrupted whirling or vibratory motion (Fig. 184,/). 
The constant vibrations of these cilia cause a continued 
current of water over the surface of the body. Fresh water 
is constantly conveyed to the surface of the skin by this 
current, thus permitting respiration in its simplest form (skin- 
respiration). A similar ciliated covering, just as is seen in 
the extant Gliding-worms of our fresh-water seas, pre- 
sumably covered our extinct ancestors of the Primitive 



78 THE EVOLUTION OF MAN. 

Worm group, the Archelminthes. They inherited this 
ciliated dress directly from the Gastrsea. 

If we now make various vertical sections (longitudinal 
and transverse) through the simple body of the Gliding- worms 
(and that of the Archelminthes which are certainly very 
closely allied to the former), we soon discover that their 
internal structure is considerably higher than that of the 
Gastrseads. We first observe that the two primary germ- 
layers (inherited from the Gastriea) have differentiated into 
several cell-strata. The skin-layer and the intestinal layer 
have each split into two strata. The four secondary germ- 
layers, which are thus produced, are the same that we found 
resulted from the first differentiation of the two primary 
germ-layers in the embryo of the Vertebrate also. (Cf the 
transverse sections through the larval Amphioxus and 
Earth-worm, Figs. 50 and 51, p. 236, and Plate IV. Fig. 2; 
Plate V. Fig. 10.) 

The highly important histological differentiation of these 
four secondary germ-layers led directly to further organolo- 
gical processes of differentiation, by which the organism of 
the Primitive Worms was soon considerably raised above 
that of the Gastrseads. In the latter there was really, in 
a morphological sense, but a single organ, the primitive intes- 
tine, with its mouth-opening. The whole body was nothing 
but an intestinal canal ; the intestinal wall was at the 
same time the wall of the body. Of the two cell-layers^ 
forming this intestinal wall, the inner accomplished the 
functions of nutrition, the outer those of motion and 
covering. As some of the cells of the primary germ-layers 
developed into egg-cells, and others into sperm-cells, these 
layers also performed the function of reproduction. In the 



GLIDING-WOKMa 79 

Primitive Worms, however, simultaneously with the forma- 
tion of the secondary germ-layers, these various functions 
also began to be distributed to various organs, which detached 
themselves from the original main organ, the primitive in- 
testine. Special organs originated for reproduction (sexual 
glands), for secretion (kidneys), for motion (muscles), and 
for sensation (nerves and sense-organs). 

In order to obtain an approximate picture of the sim- 
plest form in which all these various organs first appeared 
in the Primitive Worms, it is only necessary to examine 
the most imperfect forms of Gliding- worms (Turhellaria), as 
they exist at the present time in salt and fresh water. They 
are mostly very small and insignificant Worms of the simplest 
form, many being scarcely a millimetre or a few millimetres in 
length. In the simplest species of Gliding- worms the greater 
part of the oval body is occupied by the intestinal canal. 
This is a very regularly shaped pouch with an opening, re- 
presenting both mouth and anus (Fig. 184, m). At the 
anterior section of the intestinal tube, which is separated 
as a throat (pharynx, sd), the fibrous layer is very thick, 
a thick muscular layer. Immediately outside the intestinal- 
fibrous layer lies the skin-fibrous layer, which in most 
worms appears as a large skin-muscle sac. Above the 
throat in Gliding-worms a nerve system of the simplest 
form is already visible in front, a pair of small nerve- 
knots, or ganglia, which from their position are called the 
"upper throat ganglia," or " brain " (Fig. 185, g). Delicate 
nerve-threads {n) pass from this to the muscles and to the 
ciliated skin-sensory layer. A pair of quite simple eyes 
(au) and nose-pits (no) are to be found in a few Gliding- 

worma The Flat-worms are also universally provided with 
30 



So 



THE EVOLUTIOX OF MAN 



a pair of simple kidney-canals ( " excretory organs " ), in 
the form of two long, thin, glandular tubes, which traverse 
the right and left sides of the intestine and open at the 
hinder end of the body (Fig. 184, nm). We found that the 



■w> 





Fig. 184. — A simple Gliding-worm (Rhabdocoslum): w, mouth; sd, throat- 
epithelium ; S7n, throat-muscles ; d, stomach-intestine ; 7ic, kidney ducts ; 
nm, opening of the kidneys ; an, eye ; 7ia, nose-pit. 

Fig. 185. — The same Gliding-worm, showing the remaining organs : g, 
brain; au, eye; na, nose-pit; n, nerves; h, testes; ^, male opening j 
?> female opening j e, ovary ; /, ciliated outer-skin. 



STRUCTURE OF THE GLIDINO-WORMS. 8l 

two primitive kidney canals in the vertebrate embryo 
also appeared at a very early period, shortly after the first 
differentiation of the middle germ-layer {mesoderTna). The 
appearance of these at so early a period shows that the 
kidneys are very important primordial organs. It also 
shows their universal existence in all Flat- worms ; for even 
the Tape-worms, which, in consequence of the adoption of a 
parasitic mode of life, have lost the intestine, yet have the 
two secreting primitive kidneys, or " excretory ducts." The 
latter seem, therefore, to be older and of greater physiologi- 
cal importance than the blood-vessel system, which is wholly 
wanting in the Flat- worms. The sexual organs appear 
in many of the Gliding- worms in a very complex form ,' 
while in others their form is very simple. Most of them 
are hermaphrodites ; that is, each individual worm has 
both male and female sexual organs. In the simplest 
forms we find a testis in the anterior part (Fig. 185, h), 
a single or double ovary behind (a). One of these simplest 
existing Acoelomi, such as we find among the lowest Rhab- 
docoela, may give us an approximate idea of the structure 
of the Primitive Worm, which forms the sixth stage in 
the human pedigree. 

These ancestors of the human race, which, on account 
of their general organization, must be placed among the 
Bloodless Worms {Acodomi), must have been represented 
during the Archilithic Epoch by a large number of various 
Worm forms. The lowest of these must have been directly 
connected with the Gastrseads (the fifth ancestral stage); the 
most highly developed must, on the other hand, have been 
directly connected with the Coelomati (the seventh stage), 
Afly however, our present knowledge of the Comparativt 



8a THE EVOLUTION OF MAN. 

Anatomy and Ontogeny of the Acoelomi is very fragmen 
tary, and much too imperfect to enable us to point with 
certainty to the series of the various stages, we will not 
attempt a detailed arrangement of them. "We will turn 
instead to the seventh stage in the human pedigree, which 
belonged to the multiform group of the Blood-bearing 
Worms (Coelomati). 

The great organic advance in structure by which the 
Blood-bearing worms, or Coelomati, developed from the 
older Bloodless Worms, or Acoelomi, consisted in the for- 
mation of a body-cavity (coeloma), and of a nutritive juice 
filling the latter, the first blood. All the lower animals 
with which we have yet occupied ourselves in our Phy- 
logeny, all the Primitive Animals and Plant-animals, are, 
like the Acoelomi, bloodless and without a body-cavity. In 
the formation of a special vascular system, the earliest 
Coelomati made a very great advance. Much of the com- 
plexity in the organic structure in the four higher tribes of 
animals is based on the differentiation of the vascular 
system, which they have inherited from the Blood-bearing 
Worms. 

The first development of a true body-cavity (axlomd) 
is referable to the separation of the two fibrous layers ; to 
the formation of a spacious cavity between the outer skin- 
fibrous layer and the inner intestinal-fibrous layer. In the 
fissure-like gaps, which formed between the two germ-layers, 
a juice collected, which penetrated through the intestinal 
wall. This juice was the first blood, and the gaps between 
the two germ-layers formed the first rudiment of the body- 
cavity. The union of these gaps formed the simple coelom, 
the large cavity, containing blood or lymph, which plays m 



BLOOD-BEARING WORMS. 83 

important a part in all the higher animals as the receptacle 
of the very extensive intestines. The formation of this 
coelom, and of the blood-vessels developed in connection with 
it, exercised a very great influence on the further evolution 
of the animal organization. The most important result was, 
that it allowed the conveyance of rich nutritive juices to 
those parts of the body lying near the circumference, and 
developing at a considerable distance from the intes- 
tinal canal. The intimate correlation, or reciprocity of the 
parts, necessarily occasioned, in direct connection with the 
progressive development of the blood-vessel system, many 
other important advances in the structure of the body of 
the Blood-bearing Worms. 

Just as among the Acoelomi, so also among the Coelomati, 
the pedigree of our race must have passed through a large 
number of diverse ancestral stages. But among extant 
Coelomati (which form but a very small fraction of this once 
multiform group), there are but very few Worms which can 
with certainty be regarded as nearly allied to the long- 
extinct ancestors of Man. In this respect, but a single 
class of Coelomati is really of prominent importance ; these 
are the Mantled Animals {Tunicata), to which belong the 
Ascidia already known to us. Our careful examination of 
the structure and germ-history of the Ascidian and the 
Amphioxus have shown the extreme importance of these 
very interesting animal forms. (Cf. Chapters XIII. and 
XIV.) That examination fully justifies us in asserting 
that among the ancestors of the Vertebrates (and therefore 
of Man) there was an unknown extinct coelomate species, 
to which the nearest allied form among extant animals is 
the Appendicularia (Fig. 187), of which we have already 



84 THE EVOLUTION OF MAK. 

spoken, and the tailed Ascidian larva. We will for the 
present call this kind of Worm, which was primarily dis- 
tinguished by the possession of a notochord, the Chorda- 
animal (Chordonium). The Ascidians on the one hand, and 
the Vertebrates on the other, developed, as two diverging 
branches, from these Chorda-animals. The common parent- 
form of the Chorda-animals themselves was a coelomate form, 
which finally must have descended from the Acoelcmi, and 
from the Archelminthes. 

Many connecting intermediate forms must, of course, have 
existed between these two groups of Worms, between the 
Primitive Worms and the Chorda-animals. Unfortunately, 
however, zoological knowledge is at present especially im- 
perfect with regard to these important intermediate forma 
of the multiform Worm tribe. For very evident reasons, 
none of these Worms could leave fossil remains. For, like 
the great majority of other Worms, they had no hard parts 
in their bodies. Most even of the known fossil Worms 
are worthless, for they tell us little or nothing of the most im- 
portant structural features of the soft body. Fortunately, 
however, we can in great measure satisfactorily fill the con- 
siderable palseontological gap in this part of our pedigree, 
with the help of the Comparative Anatomy and Ontogeny of 
Worms. If, on the one hand, we examine the structure and 
mode of development of the lower Worms from the Gliding- 
Worms (Turbellaria), and, on the other hand, the Anatomy 
and Ontogeny of the Ascidians, it is not difiicult, step by 
step, to re-construct in imagination the connecting inter- 
mediate forms, and to insert a series of extinct ancestral 
forms between the Acoelomi and the Chordonia. This 
series of forms under the name of Soft-worms {Scolecida) 



DEVELOPMENT OF CHORDA- ANIMALS. 85 

we will consider as the seventh stage in the human 
pedigree. 

An examination of the Comparative Anatomy of the 
various Scolecid forms, which we might perhaps distinguish 
here, would lead us much too far into the difficult details 
of the Comparative Anatomy and Ontogeny of the Worms. 
For our purpose it seems more important to call attention 
to those phylogenetic advances, by means of which the 
organization of the earliest Blood-bearing Worms was in 
the end elevated to that of the Chorda-animals. The Com- 
parative Anatomy and Ontogeny of the Gliding-worms 
and of the Ascidians justify us in giving special weight to 
the sio:nificant differentiation of the intestinal canal into two 
distinct divisions ; into an anterior division (the gill-intes- 
tine), which accomplishes respiration, and a posterior divi- 
sion (the stomach-intestine), which accomplishes digestion. 
As in Gastrseads and Primitive Worms, so also in the Ascidian 
larva, the intestinal canal is at first a simple pouch-like 
body, provided merely with a mouth-opening. A second 
opening, the anus, does not develop till a later period. Gill- 
openings afterwards appear in the anterior section of the 
intestinal canal, by which the whole anterior intestine is 
transformed into a gill-body. This remarkable arrange- 
ment is, as we found, quite peculiar to Vertebrates, and, 
except in the Ascidians, occurs nowhere else. Among extant 
Worms there is, however, a single isolated and very remark- 
able Worm form, which in this respect may be regarded 
as distantly allied to the Ascidia and to Vertebrates, and 
perhaps as an off-shoot from the Soft-worms (Scolecida). 
This is the so-called "Acorn-worm" {BalanoglossiLS, Fig. 
186), which Kves in the sand of the sea-shore. The in- 



96 



THE EVOLUTION OP MAN. 



leresting points connecting this with Ascidians and the 

Skull-less Animals (Acrania) 
were first accurately observed 
and explained by Gegenbaur. Al- 
though this singular Balanoglossus 
is in many other respects peculiar 
in its organization, so that Gegen- 
baur rightly ranked it as the re- 
presentative of a special class 
(Enter opneusta), yet the structure 
of the anterior section of the in- 
testinal tube is exactly similar to 
that of Ascidians and SkuU-less 
Animals (k), a gill body, the walls 
of which are pierced on either side 
by gill-openings and are supported 
by gill-arches. Now, although the 
Acorn-worm in other points of its 
structure may differ very con- 
siderably from those extinct Soft- 
worms (Scolecidce), which we must 
regard as direct ancestors of our 
race, and as intermediate links 
between the Primitive Worms 

Pig. 186. — A young Acorn -worm (Bal- 
anoglossus). (After Alexander Agassiz.) 
r, acorn-like proboscis ; h, collar ; k, gill 
openings and gill-arches of the anterior in- 
testine, in a long row one behind another 
on each side ; d, digestive posterior intefr- 
tine, filling the greater part of the body- 
cavity ; V. intestinal, vessel, lying: beti 
two peirailel loiOs ot sKm.; a, tosua. 




sorr-woBMB. 9f 

and the Chorda-animals, yet, in virtue of this characteristic 
structure of the gill-intestine, it may be considered a re- 
motely allied collateral line of the Soft-worms. The 
development of an anus (Fig. 186, a) at the end opposite 
to the mouth, is also a considerable advance in the struc- 
ture of the intestine. The further development of the 
blood-vessel system in the Acorn-worm also indicates a 
marked advance. In the ciliary surface of the skin, on 
the contrary, it recalls the Gliding- worms. The sexes are 
separated, while our scolecid ancestors were probably 
hermaphrodite.^^ 

From a branch of the Soft- worms, the group of Chorda- 
animals (Ghordonia), the common parent-group of the 
Mantle-animals and Vertebrates also developed. The process 
which primarily led to the development of this important 
group of the coelomati, was the formation of the inner 
axial skeleton (the notochord, or chorda dor sails), wliich 
at the present day we find permanently retained in its 
simplest form in the lowest Vertebrate, the Amphioxus. 
We saw that this notochord is already found in the tailed 
and free-swimming larva of the Ascidian (Plate X. Fig. 5). 
The chorda does, indeed, serve specially as a support for 
the rudder-like tail of the larval Ascidian, but its anterior 
extremity passes in between the intestinal and medullary 
tubes within the actual body of the larva. A transverse 
section of this larva therefore shows that arrangement of 
the most important organs which is characteristic of the 
vertebrate type : in the centre is the firm notochord, which 
supports the other organs and serves especially as a base 
and point of attachment for the motive trunk muscles ; 
above this notochord, on the dorsal side, is the central 



SS THE EVOLUTION OF MAN. 

nervous system in the form of a medullary tube ; below, on 
the ventral side, is the intestinal tube, the anterior half of 
which is a respiratory gill-intestine, its posterior half a 
digestive stomach-intestine. It is true that the free- 
swimming larva of the extant Ascidian possesses this typical 
vertebrate character only for a short time ; it soon relin- 
quishes its free roving mode of life, puts off its oar-like tail 
with the notochord, adheres to the bottom of the sea, and 
then undergoes that very great retrogression, the surprising 
final result of which we have already observed (Chapters 
XIII. and XIV,). Nevertheless, the Ascidian larva, in its 
very transitory evolution (for a brief space), affords us a 
picture of the long extinct Chordona-form, which must 
be regarded as the common parent-form of Mantle-animals 
and Vertebrates. There is even yet extant a small and 
insignificant form of Mantle-animal which throughout life 
retains the structure of the Ascidian larva with its oar- 
like tail and its free-swimming mode of life, and which 
reproduces itself in this form. This is the remark- 
able Appendicularia (Fig. 187), which we have already 
examined. 

If we ask ourselves what conditions of adaptation could 
possibly have had so remarkable a result as the develop- 
ment of the notochord, and the modification of a branch 
of the Soft- worms into the parent-form of the Chorda- 
animals, we may with great probability answer, that this 
result was effected by the habituation of the creeping 
Soft-worm to a swimming mode of life. By energetic and 
continued swimming movements, the muscles of the trunk 
would be greatly developed, and a strong internal point oi 
attachment would be very favourable to this musculai 



THE ASCIDIANS. 89 

activity. A support of this kind might arise by enlarge- 
ment and concrescence of the germ-layers along the longi- 
tudinal axis of the body; and the differentiation of an 
independent bony cord from this axial cord gave rise to the 
notochord. (Cf Fig. 88, 89, vol. i. pp. 300, 301.) In corre- 
lation to the formation of this central notochord, the simple 
nerve-ganglia, lying over the throat in the Soft-worms, 
lengthened into a long nerve-cord, reaching from front to 
rear, above the notochord ; in this way, the medullary tube 
originated from the " upper throat ganglia." 

As we have already minutely considered the great 
lignificance of the Ascidians (Fig. 188) in this respect, as 
well as their close relations to the Amphioxus (Fig. 189). 
we will not tarry longer over this point now. I will 
repeat, that we must by no means regard the Ascidian 
OS the direct parent-form of the Amphioxus and of the 
other Vertebrates. On the contrary, we assert that, on 
the one hand the Ascidians, and on the other the Ver- 
tebrates, have both descended from one unknown 
Worm form, which has long been extinct ; the nearest 
relatives of this among existing animals are the Ascidiai- 
larvae and the Appendicularia (Fig. 187). This unknown 
common parent-form must have belonged to the group of 
Chorda-animals, which we pointed out as the eighth 
ancestral stage in the human pedigree. ^^ Although we 
cannot form an entirely satisfactory idea as to all points 
of external and internal structure of this Chorda-animal, 
there is no doubt that, like its near relatives, the 
Mantle-animals, and like the preceding ancestral stage 
represented by the Soft- worms and Primitive Worms, it 
must be classified in the natural system of the animal 



90 



THE EVOLUTION OF MAN. 



kingdom as a genuine Worm. The difi'erence between it 
and other genuine Worms cannot have been greater than is 







v.d; 



^-(y 



'm. 



Fio. 187. — Append icularia, seen from the left side : m, montli ; k, giU- 
intestine ; o, oesophagus ; v, stomach ; a, anus ; n, nerve-ganglia (nppex 
throat-knots) ; g, ear-vesicle ; /, ciliated groove under the gill j fc, heart f 
(, testes ; «, ovary ; c, notochord ; «, tail. 

Fig. 188. — Structure of an Ascidian (seen from the left, z» in Fig. 153 
and Fig. 14, Plate XI.) : sb, giU-sao j v, stomach ; t, large intestine j c, 
heart ; t, testes ; vd, seed-duct ; o, ovary j o\ matured eggs in the body. 
oavitj. (After Milne Edwards.) 



THE AMPHIOXU& 



91 



11 



111 



fch* difference between the extant Tape- worms and Ringed 
Worms (Annelida). Moreover, in a certain sense we may 
regard the extant Appendicularia as a last remnant of the 
Chordonia class. 

We have now studied the most import- 
ant animal forms which occur in the pedigree 
of the human race, and which, in the zoo- 
logical system, must be classed among the 
Worms. In leaving this lower class, and 
tracing our ancestry henceforth exclusively 
within the vertebrate tribe, we at once ^ 
leave behind the great majority of animal 
(brms, which branched off from the worm 
Liibe in entirely different directions. When, 
ill a previous chapter (IX.), the vertebrate / 
ature of man was proved, it was incidentally 
entioned that the very great majority of « 
animals are in no way directly allied to our , 
tribe. The parent-forms of the three other ' 
higher Animal tribes,the Articulated Animals 
{Arihro'poda), Star-animals (Echinoderma), 
and Soft-bodied Animals (MoUusca), like 
the vertebrate tribe, originated from the 

Fig. 189. — Lancelet (^Amphiomus Icmceolatus), twice 
the actual size, seen from the left (the longitudinal 
axis is represented vertically, the mouth turned up- 
ward, the tail downward, as in Plate XI. Fig. 15) : 
a, mouth-opening, surrounded by cilia ; h, anal open, 
iug ; c, ventral opening {Porus ahdominalia) ; d, gill- 
body I 0, qtomach j /, liver-coecum ; g^ large intes- 
tine ; h, coelom : », notochord (under it the aorta) ; 
k, trches of the aorta ; I, main gill-artery ; tn, ewellingi 
on its branches; n, hollow Tttiii} 0, intoitinal Tttin. 



( 92 ) 



TABLE XVIII. 

Bj^tematio Survey of the Phylogenetio System of the Animal Kingdom, 
founded on the Gastraea Theory and the Homology of the Germ-layers. 



Tribes «r Phyla 

<tfthe 

tMimaX Kingdom. 



Main Classes or 

Branches of the 

Animal Kinydom. 



Classet 

of the 

AnifMil Kingdmn. 



Systematic Namtt 

ofthd 

Classes. 



First Sub-kinqdom : Primitive Animals (Protozoa). 
Animals without germ-layers, intestine, or true tissues. 



A. 

^rttnittbe 
Animals 
Protozoa 



Egg-animals 
Ovularia 



1. Monera 

2. AmcebsB 

3. Gregarinae 



IL Infusorial animalt t 4. Sucking InfuMri* 



Infusoria 



It; 



Ciliated Infusoria 



1. Monera 

% Lobosa 
S. Gregarina 

4. AcineUs 

5. Ciliata 



Second Sub-kingdom : Intestinal Animals (Metazoa). 
Animals with two primary germ-layers, intestines and tissues. 



B. 

plant* 
Animals 
Zoophytes 



C. 

SKorms 
VermeB 



D. 

Soft^bDtiteti 
Animals 
Mollusoa 

E. 
Star==<ammals 
Echinoderma 

F. 

^rticulatrt 

Animals 

Arthropoda 



G. 

Ftrtebrate 

'Enimals 

y«rtebrata 



III. Sponges 
Sponffia 

TV. Sea-nettles 
Acalephoe 

T. Bloodless worms 
AcaUnna 



{: 



VI. 



Blood-worms 
CcBlomati 



\ 



18. 

19. 

V20. 

/ VU. Headless shell-fish r 21. 
Acephala \ 22. 

Vni. Head-bearing 
shell-lish 
Eucephala 

IX. Ringed -arms 
Colobrachia 
X. Armless 
Lipobrachia 

XI. GiU-breathers 
Carides 



Primitive 
animals 
Sponges 

{8. Corals 
9. Hood-jeUiet 
10. Comb-jellia 

(11. Primitive worms 
12. Flat-worms 
/13. Round- worms 
1 14. Arrow-worms 
I 15. Wheel-animalcules 
J 16. Moss-polyps 
17. Mantle-animals 
Acorn-worms 
Star-worms 
Ringed-wormi 

Lamp-shells 
Mussels 



intestiasl t. Gastr»adi 






23. 
24. 



Snails 
Cuttles 



t. Porifera 
•. Coralla 
f . Hydromednsa 
!•. Ctenophora 

11. Archelminthes 

12. Plathelmlnthes 

13. Nemathelminthes 

14. Choetognathi 

15. Rotatoria 

16. Bryozoa 

17. Tunicata 

18. Enteropneusts 

19. Gephyrea 

30. Annelida 

31. Spirobranchla 

32. LamellibranchiR 

23. Cochlides 

24. Cephalopoda 



Xn. Tube-breathers 
Tracheata 



\ 26. Sea-lilies 

f 27. Sea-urchins 

1 28. Sea-cncumbefs 

i 29. Crabs 

I 30. Spiders 

< 31. Centipedes 

32. Flies 



26. 
26. 
37. 
38. 



Asterida 
Crinoida 
Ecblnida 
Holotharice 



39. Cmstaoea 



30. 

31. 
32. 



Arachnida 
Myriopoda 
Insect* 



Xni. Skull-less 
Acrania 
XIV 



/ 33. Tube-hearts (Lsnos- 
l lets) 

Single -nostrilled f 34. Round-moutbs 
Monorrhina I (Lampreys) 

35. Fishes 

36. Mud-fish 

37. Amphibians 

38. Reptiles 

39. Birds 

40. Mammals 



XV. Amnion-lesB 
Ancumnia 

xn. AmnioD-animals ^ 
Ammiota 



33. Leptocariis 
M. Cjclostoma 

35. Pisces 

36. Dipneusta 

37. Amphibia 

38. Reptilia 

39. Aves 

40. MsmmsHs 



( 93 ) 

TABLE XIX. 

tfonophyletio Pedigree of the Animal Kingdom, founded on the GastrtM 
Theory and the Homology of the Germ-layers." 



It 

I 



§ 



II 

IS 
■<^ 

•S'2 > 

^r 

5 ♦* 5 

N ►:; OJ - 
•<&^ >< Oi 

(, v-^ a> ri 

eg gO 



H 



I 



I. 






1 ai ^ 05 

o 



^ to 4 



^5* - 

S a** M 
S C S o3 

15 



fi) 



Articalates 
Arthropoda 



Vertebrates 
Vertebrata 



St&r-anfmals 
Echinoderma 



v^ 



Soft-bodied Aninuds 
Mollusca 



Coelomati. 
( Wormt with body-cavity) 



Plant-animals 

Zoophyta 
(^CoBlenUratd) 



SpongM 

Spongiee 



Sea-nettles 
(^Acalephce) 



Flat Womn 
PlathelmlQtbe 



Protascus 



GaBtrjea radialis 
{stationary) 



Acoelomi 
iWorwu without body-eavUjf) 



Prothelmii 

Gastrsea bilateraUs 
{crawling) 



Gastraea 
^Ontogeny: Gattridd) 



Primitiye Anim^t* 
Protozoa 



PlanaeadA 
{OtUoffeny: BUutuia') 



CUiAU 



Adseto 



OKgarlnse 



InfusoiiA 



SynamoebA 
{Ontogeny: Morula') 



AmoeUaa 



\ 

AmoebsB 

(Ontogeny: CytuU) 



Monera 
{Ontogeny: MtntnltQ 



94 THE EVOLUnOW OF MAN. 

worm tribe ; but the parent-forms of the three formei 
belong to worm-groups quite distinct from that of the 
Chordonia. It is only far down at the common root of the 
group of Coelomati, that we assume a common source for 
these various tribal forms. (Cf. Tables XVIII. and XIX.) 
It is especially necessary to remember that there is no 
direct blood-relationship between Vertebrates and Articu- 
lated Animals. 

The Articulated Animals (Arthropoda), to which the 
most comprehensive of all classes of animals, that of Insects, 
and also the Spiders, Centipedes, as weU as the Crabs, or 
Crustaceans, belong, are descendants of articulated Worms, 
the nearest allies of which are the extant Ringed Worms 
(Annelida). The tribe of Star-animals (Echinoderma), 
which includes the Star-fishes, Sea-lilies, Sea-urchins, and 
Sea-cucumbers, must also have descended from similar articu- 
lated Worms."^ The parent-form of the Soft-bodied Animals 
(Mollwsca), which include the Cuttles, Snails, Mussels, and 
Lamp-shells, must also be sought among the Worms. But 
the Coelomati, from which these three higher animal tribes 
originated, differed entirely in character from the Chorda- 
animals. Unlike the latter, they never developed a noto- 
ohord. In them, the anterior section of the intestinal tube 
was never modified into a gill-body with gill-openings; nor 
were the upper throat-ganglia developed into a medullary 

tube. In a word, in Articulated Animals, Star-animaJs, and 

if 

Soft-bodied Animals, as well as in their ancestors among 
the Blood-bearing Worms, the typical structural peculiari- 
ties which are exclusively characteristic of the vertebrate 
tribe and of their immediate invertebrate progenitors, were 
never present Thus the great majority of all Miimalfl are 



DEVELOPMENT OF VERTEBRATES FROM INVERTEBRATES. 95 

in no way the subject of our further investigations, which 
are only concerned with the Vertebrates. 

The development of the Vertebrates from the Inverte- 
brates most nearly related to them, the Chorda- Animals, 
occurred millions of years ago, during the Archilithic Epoch, 
(See Table XII., p. 11.) This is unmistakably shown by 
the fact that the most recent sedimentary rock-strata 
which were deposited during that immense period of time, 
the higher layers of the Upper Silurian formation, contain 
remains of fossil Fishes (Primitive Fishes, Selachii). As 
these Fishes, although they belong to the lowest stage of 
the Skulled Animals (Craniota), yet possess a compara- 
tively high organization, and as they must necessarily have 
been preceded by a long progressive series of lower Skull- 
less Vertebrates, we must attribute the origin of the oldest 
Skull-less Animals (A crania) from the Chorda-animals to 
a much earlier part of the Archilithic Epoch. Therefore, 
not only all the invertebrate ancestors of our race, but also 
the earliest form of our vertebrate progenitors must have 
developed in that primordial time, which includes the 
Laurentian, Cambrian, and Silurian Periods. (C£ Tables 
XIIL, XIV., and XVI., pp. 12, 19, 44.) 

Unfortunately, Palaeontology can give us absolutely no 

information with regard either to the structure of our oldest 

vertebrate ancestors, or to the time of their appearance; 

for their bodies were as soft and as destitute of hard 

parts capable of fossilization, as were the bodies of all 

our preceding invertebrate ancestors. It is, therefore, not 

surprising, but quite natural, that we find no fossil 

remains of the former in the Archilithic formations. The 

Fishes in which the soft cartilaginous skeleton was partly 
40 



96 THE EVOLUTION OF MAN. 

modified into hard bone, are the earliest Vertebrates capable 
v./ leaving petrified records of their existence and structure. 
Fortunately, this want is more than counterbalanced 
by the much more important testimony of Comparative 
Anatomy and Ontogeny, which henceforth form our 
safest guides within the Vertebrate pedigree. Thanks to 
the classic researches of Cuvier, Johannes Miiller, Huxley, 
and especially of Gegenbaur, we are in possession of such 
extensive and instructive records of creation in this most 
important branch of tribal history, that we can prove at 
least the more significant features in the development of our 
Vertebrate ancestors, with the most gi^atifying certainty. 

The characteristic peculiarities by which Vertebrates 
in general are distinguished from all Invertebrates, engaged 
our attention some time ago, when we examined the structure 
of the ideal Primitive Vertebrate (Figs. 52-56, p. 256). The 
most prominent characters were as follows: (1) the formation 
of the notochord between the medullary and intestinal tubes; 
(2) the differentiation of the intestinal tube into an anterior 
gill-intestine and a posterior stomach-intestine ; (3) the 
inner articulation, or formation of metamera. The Verte- 
brates share the first two qualities with the larval Ascidians 
and with the Chorda-animals ; the third quality is entirely 
peculiar to them. Accordingly, the most important struc- 
tural advance, by which the earliest vertebrate forms origin- 
ated from the most nearly allied Chorda-Animals, consisted 
in an internal metameric structure. This showed itself 
first most distinctly in the articulation of the muscular 
system, which broke up on the right and left into a series 
of consecutive muscular plates. At a later period the 
articulation declared itself prominently in the skeleton, and 



CLASSIFICATION OF VERTEBRATB8L 97 

nervous and blood-vessel systems. As we have already 
seen, this process of articulation, or metameric formation, 
must essentially be regarded as terminal germination. 
Each distinct trunk-segment, or metameron, represents an 
individual. Thus the Vertebrates with their internal 
segmentation stand in a similar relation to their inarticulate 
Invertebrate ancestors, the Chorda Animals, as do the out- 
wardly segmented Ringed Worms (Annelida) and Articu- 
lated Animals (Arthropoda) to the simple inarticulate 
Worms from which they originated. 

The tribal history of Vertebrates is rendered much more 
intelligible by the natural classification of the tribe which 
I proposed first in my Generelle Morphologie (1866), and 
afterwards improved in many ways in " The Natural History 
of Creation" (Chap. XX., p. 192, etc.). In accordance with 
that, existing Vertebrates must be divided into at least 
eight classes, as follows : — 

STSTEMATIO SURVEY OF THE EIGHT CLASSES OF 

VERTEBRATES. 

A. Sknll-lfiM (^Aerania) 1. Tnbe-hearted 1. Leptocardia 

ia. Single-nostiilled {Monorhina) 2. Round-moaths 2. C7ck)*toina 

/ L [3. Fishes 3. Pisces 

1 Amnion-less J. 4. Mud-fishes 4. Dlpneusta 

b. Doable-nostrilldd j Anamnia [ 5. Amphibians 6. Amphibia 

Awiphirhina { II ^6. Rpptiles 6. Reptilia 

f With Amnion < 7. Birds Y. Aves 

V Amniota { 8. Mammals 8. Mammalia 

The whole Vertebrate tribe may primarily be divided 
into the two main sections of the Skull-less and the 
Skulled Vertebrates. Of the earlier and lower section, that 
of the Skull-less (Acrania), the Amphioxus is alone extant. 
To the more recent and higher section, the Skulled (Cra- 
niota), belong all other existing Vertebrates up to Man. The 



98 THE EVOLUTION OF MAN. 

Craniota branched off from the Acrania, as these did from 
the Chorda Animals. Our exhaustive study of the Compara- 
tive Anatomy and Ontogeny of the Ascidian and the 
Amphioxus have already afforded proof of this relation. (Cf 
Chapters XIII. and XIV., and Plates X. and XI. with the 
explanations.) I will only repeat, as the most important 
fact, that the Amphioxus develops from the egg in exactly 
the same way as the Ascidian. In both, the original Bell- 
gastrula (Figs. 4 and 10) originates in an exactly similar 
manner, by primordial cleavage from the simple parent-cell 
(Figs. 1 and 7). From this originates that remarkable larva, 
which develops a medullary tube on the dorsal side of the 
intestinal tube, and between the two a notochord. At a 
later period, both in the Ascidian and in the Amphioxus, the 
intestinal tube differentiates into an anterior gill-intestine 
and a posterior stomach-intestine. In accordance with the 
fundamental principle of Biogeny, from these very important 
facts we may deduce the following statement of great phylo- 
genetic importance : the Amphioxus, the lowest Vertebrate 
form, and the Ascidian, the most nearly allied Invertebrate 
form, have both descended from one single extinct Worm 
form, which must have possessed the essential structure of 
the Chorda Animals. 

The Amphioxus, as has already been often shown, is 
of extreme importance ; not only because it thus fiUs the 
great gap between the Invertebrates and the Vertebrates, 
but also because it represents, at the present time, the 
typical Vertebrate in its simplest form; and because it 
directly affords the best standpoint from which to examine 
the gradual historic evolution of the whole tribe. If the 
Btructure and germ-history of the Amphioxus were un^ 



THB AMPHIOXUS AS THE ANCESTOR OF MAN. 99 

known to us, the whole subject of the development of 
the Vertebrate tribe, and thus of our own race, would Ije 
enveloped in an impenetrable veil. The accurate anatomical 
and ontogenetic knowledge of the Amphioxus, attain'.'' 
during the last few years, has alone pierced that heavy veil 
formerly supposed to be impenetrable. If the Amphioxus i 
compared with the developed Man or any other of tl. 
higher Vertebrates, a great number of striking dissimilarities 
will be seen. The Amphioxus has no specialized head, nu 
brain, no skull, no jaws, no limbs ; it is without a central- 
ized heart, a developed liver and kidneys, a jointed vertebral 
column ; every organ appears in a much simpler and more 
primitive form than lq the higher Vertebrates and in Man 
(Cf. Table X., vol. L p. 466.) And yet, in spite of all thest 
various deviations from the structure of other Vertebra te^ 
the Amphioxus is a genuine, unmistakable Vertebra it- 
and if, instead of the developed Man, the human embr\ > 
at an early period of its Ontogeny is compared witi 
the Amphioxus, we shall find perfect parallelism betweei 
the two in all essential points. (Cf Table IX., vol. L p. 465.; 
This highly important parallelism justifies the conclusion 
that all the Skulled Animals (Craniota) have descended 
from a common primaeval parent-form, the structure of 
which was essentially that of the Amphioxus. This parent- 
form, the earliest Primitive Vertebrate, possessed the 
peculiar characters of the Vertebrates, and yet was without 
all those important peculiarities that distinguish the Skulled 
Animals from the SkuU-less. Although the Amphioxus ap- 
pears peculiarly organized in many respects, and although 
it may not be regarded as an unmodified descendant of the 
Primitive Vertebrate, yet it must have inherited from the 



100 THE EVOLUTION OF MAN. 

latter the distinguishing characteristic features already 
mentioned. We cannot therefore say that the Amphioxus ia 
the progenitor of the Vertebrates ; but we may certainly say 
that the Amphioxus of all known animals is nearest allied 
to this progenitor ; both belong to the same limited family 
group, to the lowest Vertebrate class, that of the Skull-less 
Animals (Acrania). In the human pedigree, this group 
forms the ninth stage of the ancestral chain, the first among 
Vertebrate ancestors. From this Skull-less group was 
ieveloped the Amphioxus on the one side, and on the other 
fche parelit-form of the Skulled Animals (Craniota). 

The comprehensive group of the Skulled Animals 
includes aU known Vertebrates, with the single excep- 
tion of the Amphioxus. All these Skulled Animals 
possess a distinct head, inwardly specialized from the 
trunk, and this contains a skull, enclosing a brain. This 
head also carries three of the higher sense-organs, which are 
partially wanting in the Skull-less Animals (nose, ears, and 
eyes). At first, the brain appears in a very simple form, as 
an anterior bladder-like extension of the medullary tube 
(Plate XI. Fig. 16, mj). This, however, is soon distributed by 
several tranverse grooves — first into three, and afterwards 
into a series of five consecutive brain-bladders. In the 
formation of the head, skull, and brain, together with the 
higher sense-organs, lies the most essential advance made 
by the skulled parent-form beyond its skull-less ancestors. 
Other organs, however, also soon rose to a higher grade 
of development; a compact centralized heart appeared, a 
more perfect liver and kidneys; and in other directions 
also important advance was made. 

The Skull-less Animals may be primarily subdivided 



SKULL-LESS ANIMALS. lOI 

into two differing main sections, that of the Single-nostrils 
(Monorhina), and that of the Double-nostrils (Amphirhina). 
Of the former there are but very few extant forms, which 
are called Round-mouths {Cyclostcmia). These are, however, 
of great interest, because in their whole structure they are 
intermediate between the Skull-less Animals and the Double- 
nostrils {Amphirhina). Their organization is much higher 
than that of the Skull-less Animals, much lower than that 
of the Double-nostrils ; they thus form a very welcome 
phylogenetic link between those two divisions. We may 
therefore represent them as a special, tenth stage in the 
human ancestral seriea 

The few existing species of the class of Round-mouths are 
distributed into two different orders, which are distinguished 
as the Hags and the Lampreys. The Hags {Myxinoides) 
have long, cylindrical, worm-like bodies. Linnaeus classed 
them among Worms, but later zoologists have placed them, 
sometimes among the Fishes, sometimes Amphibians, and 
again with Molluscs. The Hags live in the sea and are 
usually parasitic on Fishes, into the skin of which they 
penetrate by means of their round sucking mouths and 
their toothed tongues. They are occasionally found in the 
body-cavity of Fishes — for example, of the Cod and Stur- 
geon — having penetrated to the interior in their passage 
through the skin. The second order, that of the Lampreys 
(Petromyzontea), includes those well-known " Nine eyes," 
common at the seaside; the little river Lamprey {Petro- 
myzon Jluviatilis) and the large sea Lamprey {Fetromyzon 
marinvs, Fig. 190). 

The animals included in the two groups of the Myxi' 
noides and the PetroTnyzontes, are called Round-mouths 



102 THE EVOLUTION OF MAN. 

[Cycloetoma), from the fact that their mouth forms a circular 
or semi-circular opening. The upper and under jaws, 
which appear in all the higher Vertebrates, are completely 
wanting in the Round-mouths, as in the Amphioxus. All 
other Vertebrates are therefore distinguishable from them 
;ls "Jaw-mouthed" (Gnathostomi). The Round-mouths may 
rJso be called " Single-nostrils " (Monorhina), because they 
have but a single nasal tube, while the Gnathostomi are all 
furnished with a pair of nasal cavities, a right and a left 
nose-cavity (" Double-nostrilled," Amphirhina). But in 
addition to these peculiarities, the Jaw-mouths are also 
distinguished by many other remarkable structural arrange- 
ments, and are further removed from the Fishes than the 
latter are from Man. They must, therefore, evidently be 
regarded as the last remnant of a very old and very low 
class of Vertebrates, which are far below the structural 
stage of a genuine Fish. To mention here briefly only 
the most important, the Round-mouths are entirely with- 
out any trace of limbs. Their slimy skin is quite 
naked and smooth, without scales. They are wholly 
destitute of a bony skeleton. The inner skeleton axis is 
a very simple inarticulate notochord, like that of the 
Amphioxus. In the Lampreys alone a rudimentary articu- 
lation is indicated by the fact that upper arches appear in 
the vertebral tube proceeding from the notochord sheath. 
At the anterior end of the chorda a skull is developed in 
its very simplest form. From the notochord sheath pro- 
ceeds a small soft-membraneous skull capsule, which 
becomes partly cartilaginous: this capsule encloses the 
brain. The important apparatus of the gill-arches, the 
tongue-bone, etc., which is inherited by all Vertebrates 



LAMFBET& 



I03 



from Fishes to Man, is wholly wanting in 
the Round-mouths. They have, indeed, a 
superficial, cartilaginous gill-skeleton, but this 
is of quite different morphological significance. 
On the other hand, in them we meet, for the 
first time, with a brain, that important 
mental organ, which has been transmitted 
from the Single-nostrils up to Man. It is true 
that in the Round-mouths the brain appears 
merely as a very small and comparatively 
insignificant swelling of the spinal chord ; at 
first a simple bladder (Plate XL Fig. 16, mj), 
which afterwards separates into five consecu- 
tive brain-bladders, as in the brains of all 
Double-breathers. These five simple primitive 
brain-bladders, which reappear in a similar 
form in the embryos of all higher Vertebrates, 
from Fishes up to Man, and which undergo 
a very complex modification, remain in the 
Round-mouths, in a very low and undifferen- 
tiated stage of development. The histological 
elementary structure of the nervous system is 
also much more imperfect than in other Verte- 
brates. While in the latter the oro:an ot 
hearing ahvays has three semi-circular canals, 
in the Lampreys it has but two, and in the 
Hags but one. In most other points also, 
the organization of the Round-mouths is 

Fio. 190. — The large Sea-lamprey (Petromyzon marim 
wus), much reduced in size. A series of seven gill-opeo- 
ings are visible below the eje. 






r^ 



104 THE EVOLUTION OF KAN. 

much simpler and more imperfect, as, for instance, in the 
structure of the heart, the circulatory system, and the 
kidneys. In them, as in the Amphioxus, the anterior 
portion of the intestinal canal does, indeed, form respiratory 
gills ; but these respiratory organs are developed in a very 
peculiar way : in the form of six or seven little pouches, or 
sacs, which lie on both sides of the anterior intestine and 
communicate with the throat (pharynx) by inner openings, 
and by outer ones with the external skin. This is a very 
peculiar formation of the respiratory organs, quite cha- 
racteristic of this class of animals. They have therefore 
been called the " Pouch-gills " {Marsupohranchii). The 
absence of one very important organ found in the Fishes, 
the swimming-bladder, from which the lungs of the higher 
Vertebrates have developed, should be especially noticed. 

In their germ-history, as in their whole anatomical struc- 
ture, the Round-mouths present many peculiarities. They 
are even peculiar in the unequal cleavage of the egg, which 
most nearly approaches that of the Amphibians (Fig. 31, 
vol. L p. 203). This results in the formation of a Hood- 
gastfula, like that of Amphibians (Plate II. Fig. 11). From 
this develops a very simple organized larval form, which is 
closely allied to the Amphioxus, and which, for that reason, 
we examined and compared with the latter (voL i. p. 428, 
and Plate VIII. Fig. 16). The gradual germ-evolution of 
these larvae of the Round-mouths explains very clearly and 
unmistakably the gradual evolution of the Skulled from the 
Skull-less class of Vertebrates. At a later period, from 
chia simple Lamprey larva is developed a blind and tooth- 
less larval form, which is so very ditierent from the mature 
Lamprey that, until twenty years ago, it was generally 



ROUND-MOUTHa IO5 

described as a peculiar form of fish under the name of 
Ammocoetes. By a further metamorphosis this blind and 
toothless Ammocoetes is transformed into the Lamprey with 
eyes and teeth {Petromyzon)}^'^ 

Summing up all these peculiarities in the structure and 
embryology of the Round-mouths, we may assert that the 
oldest Skulled Animals, or Craniota, diverged in two lines ; 
one of these lines has continued up to the present time 
but little modified; it is represented by the Cyclostoma, 
or Monorhina, forming a collateral line which has made 
but little progress, but has remained at a very low stage of 
development. The other line, the direct line in the pedigi^ee 
of the Vertebrates, advanced in a straight line to the Fishes, 
and by new adaptations attained many important improve- 
menta 

In order rightly to appreciate the phylogenetic signi- 
ticance of interesting remnants of primaeval groups of 
animals, such as the Round-mouths, it is necessary to study 
minutely their various peculiar characters philosophically 
and with the aid of Comparative Anatomy. A careful 
distinction must be drawn between the hereditary cha- 
racters which have been accurately transmitted to the 
present day by heredity from common, primaeval ancestors, 
now extinct, on the one hand ; and, on the other, those 
special adaptive peculiarities which the existing remnant 
of that primaeval group have, in the course of time, gained 
secondarily by adaptation. To the latter class belong, 
for example, in the Round-mouths, the peculiar formation 
of the sino'le nostril and the round suckinor mouth: as 
well as special structural arrangements of the epidermis 
and the pouch-shaped gills. But, on the other hand, to the 



I06 THE EVOLUTION OF MAN. 

former class of characteristics, which alone have any phylo- 
genetic significance, belong the primitive formation of the 
vertebral column and the brain, the absence of the swim- 
ming-bladder, of jaws, limbs, etc. 

In the animal system, the Round-mouths are usually 
classed among Fishes; but that this is quite incorrect is 
apparent from the simple fact that, in all important and 
prominent structural peculiarities, they are further removed 
from the Fishes than the Fishes are from the Mammals and 
from Man. 



CHAPTER XVIII. 
THE PEDIGREE OF ]VIAN. 

III. Feom the Primitive Fish to the Amniotic Animal. 

Comparative Anatomy of the Vertebrates. — The Characteristic Qualities of 
the Donble-nostrilled and Jaw-mouthed : the Double-Nostrils, the Gill- 
arch Apparatus, with the Jaw-arches, the Swimming-bladder, the Two 
Pairs of Limbs. — Relationship of the Three Groups of Fishes : the Pri- 
mitive Fishes (^Selachii), the Ganoids {Ganoides), the Osseous Fishes 
(Teleostei). — Dawn of Terrestial Life on the Earth. — Modification of 
the Swimming-bladder into the Lungs. — Intermediate Position of the 
Dipneusta between the Primitive Fishes and Amphibia. — The Three 
Extant Dipneusta (Protopterus, LepidosireUy Ceratodua). — Modification of 
the Many-toed Fin of the Fish into the Five-toed Foot. — Causes and 
Effects of the latter. — Descent of all Higher Vertebrates from a Five-toed 
Amphibian. — Intermediate Position of the Amphibians between the 
Lower and Higher Vertebrates. — Modification or Metamorphosis of 
Frogs. — Different Stages in Amphibian Metamorphosis. — The Gilled 
Batrachians (Proteus and Axolotl) . — The Tailed Batrachians (Salaman. 
ders and Mud-fish). — Frog Batrachians (Frogs and Toads). — Chief 
Ghroup of the Amnion Animals, or Amniota (Reptiles, Birds, and 
Mammals). — Descent of all the Amniota from a Common Lizard.like 
Parent-form (Protamnion) . — First Formation of the Allantois and of the 
Amnion. — Branching of the Amnion Animals in Two Lines : on the one 
side, Reptiles (and Birds), on the other side. Mammals. 

** The imagination is an indispensable faculty ; for it ifl that which, by 
forming new combinations, occasions important discoveries. The naturalist 
needs both the discriminating power of abstract reason, and the generalizing 
power q{ tb0 imagination, and that the two should be harmoniously inter. 



I08 THE EVOLUTION OF MAK. 

related. If the proper balance of these faculties is deatroyed, the natnralist 
is hurried into chimerical fancies by his imagination ; while the same gift 
leads the gifted naturalist of sufficient strength of reason to the most 
important discoveries." — Johannes Mullee (1834). 

The further we proceed in human tribal history, the nar- 
rower does that part of the animal kingdom become within 
which we must look for extinct ancestors of the human 
race. At the same time, the evidence as to the history of 
the evolution of our race given by what we have called the 
records of creation, the evidence of Ontogeny, of Compara- 
tive Anatomy, and of Palaeontology, grows constantly more 
extensive, complete, and trustworthy. It is therefore 
natural that Phylogeny should assume a more definite form 
the nearer we approach the higher and the highest stages 
of the animal kingdom. 

Comparative Anatomy especially has done far more for 
our knowledge of these higher stages of evolution in the 
animal kingdom than for the lower. This important 
science, which aims at a true philosophy of organic forms, 
has made greater progress in the Vertebrate tribe than in any 
section of the Invertebrate. Cuvier, Meckel, and Johannes 
Miiller had already laid a deep and extensive foundation ; 
and now the Comparative Anatomy of Vertebrates has 
recently been powerfully advanced by the admirable inves- 
tigations of Owen and Huxley, and, especially, has been 
perfected to such a degree by the unsurpassed labours of 
Gegenbaur, that it now forms one of the strongest supports 
o£ the Theory of Descent. Relying on the evidence thus 
fiimished, we can now, with a great degree of certainty, 
recognize the most important outlines of the series of stages 
and the r&mi£cationa of the Vertebrate pedigree^ 



PRIMTnVE FISHESL lOQ 

TLat part of the animal kingdom with which we are 
now concerned has become so narrow, even before we have 
left the Archilithic Epoch, that but a single one of the 
seven tribes of the animal kingdom forms the object of our 
study. Even within this tribe we have passed the lowest 
steps, and have risen above the Skull-less (Acrania) and 
Double-nostrilled Vertebrates (Alonorhina), to the class of 
i'ishes. The latter are the first of the great main division 
of Vertebrates distinguished by mouths with jaws and by 
double nostrils (AmphirhiTia, or Onathostcmia). From Fishes 
we start again, as from that class of Vertebrates which are 
indubitably shown by Comparative Anatomy and Ontogeny 
to be the ancestral class of all higher Vertebrates, all Am- 
phirhina. Of course no existing Fish can be regarded as 
the direct parent-form of the higher Vertebrates. But it is 
equally certain that from a common extinct Fish-like 
parent-form we may trace all those Vertebrates from Fishes 
up to Man, which are included under the name of Am- 
phirhina. If this primaeval parent-form were extant, we 
should undoubtedly describe it as a genuine Fish and class 
it among Fishes. Fortunately, the Comparative Anatomy 
and Classification of the Fishes has been so far advanced 
(thanks to the labours of Johannes Miiller and Gegenbaur) 
that we can very clearly distinguish these most important 
and interesting genealogical relations. 

In order correctly to understand the human pedigree 
within the Vertebrate tribe, it is very important to bear in 
mind the distinguishing characteristics, separating Fishes 
and all the other Double-nostrils (AmphirhiTia) from 
Single-nostrilled and Skull-less Animals (Monorhina and 
Acrania). These very distinguishing characteristic marks 



no THE EVOLUTION OF MAN. 

Fishes have in common with all other Double-nostrils up 
to Man, and it is on this parallelism that we found our 
claim of relationship to Fishes. (Cf. Table X., vol. i. 
p. 466.) The following characters of the Double-nostrils 
must be especially indicated as the systematic anatomical 
features of the highest importance : (1) the double structure 
of the nose ; (2) the internal gill-arch apparatus, together 
with the jaw-arches ; (3) the swimming-bladder, or lungs ; 
and (4) the two pairs of limbs. 

As to the nasal structure, on which is based the distinc- 
tion of the Single-nostrils (Monorhina) from the Double- 
nostrils {Amphirhina), it is certainly significant that even in 
Fishes the earliest rudiment of the nose consists of two en- 
tirely distinct lateral grooves or pits in the outer surface of 
the head, just as is the case in the embryo of Man and of all 
higher Vertebrates. On the other hand, in Single-nostrils 
and Skull-less Vertebrates the first rudiment of the nose is, 
from the first, a single pit in the centre of the forehead 
region. No less important is the higher development of the 
skeleton of the gill-arch and of the jaw apparatus connected 
with it, as it occurs in all Double-nostrils from Fishes to 
Man. It is true that the primitive modification of the 
anterior intestine into the gill-intestine, which occurs even 
in Ascidians, is developed in all Vertebrates from one simple 
rudiment; and in this respect the gill-openings, which in 
all Vertebrates and also in Ascidians pierce the wall of the 
gill-intestine, are quite characteristic. But the external 
framework of the gills, which in aU Skull-less and Single- 
nostrilled Animals (Acraniota and Monorhina) supports 
the gill-body, is displaced in all Double-nostrils {Amphi- 
rhi/na) by an internal gill-skeleton which replaces the former 



DOUBLE-NOSTRILS AND SINGLE-NOSTRILS. Ill 

This internal gill-support consists of a consecutive series of 
cartilaginous arches, which are situated between the gill- 
openings within the wall of the throat (pharynx), and 
extend round the throat. The foremost of these pairs of 
gill-arches changes into the jaw-arch (maxillary arch), 
which gives rise to the upper and lower jaws. 

A third essential character by which all Double-nostrils 
are well distinguished from all those lower Vertebrates 
which we have already considered, is the formation of a 
blind sac which protrudes from the anterior portion of the 
intestinal canal, and which in the Fishes becomes the air- 
filled swimming-bladder (Plate V. Fig. 13, lit). As this 
organ, in proportion as it contains a greater or less quantity 
of air, or in proportion as this air is more or less compressed, 
imparts a higher or lower specific gravity to the Fish, it 
acts as a hydrostatic apparatus. By this means the Fish 
can rise or sink in the water. This swimming-bladder is 
the organ from which the lung of higher Vertebrates has 
developed. The fourth and last main character of Double- 
nostrils is the presence of two pairs of extremities or 
members in the primitive arrangement of the embryo ; a 
pair of fore limbs, which in Fishes are called pectoral fins 
(Fig. 191, v), and a pair of hind limbs, which in Fishes are 
called ventral fins (Fig. 191, A). The Comparative Anatomy 
of these fins is of supreme interest, because they contain 
the rudiments of all those parts of the skeleton which, in 
all the higher Vertebrates up to Man, form the skeleton or 
support of the extremities of the fore and hind limbs. In 
Skull-less and Singie-nostrilled Animals there is, on the 
contrary, no trace of these extremities. In addition to 

these four most important main characters of the Amphi- 

41 



112 THE EVOLUTION OF MAN. 

rhina, we might further mention the presence of a sym 
pathetic nerve-system, a spleen, a ventral salivary gland ; 
organs which are not represented in the lower Vertebrates 
already considered. All these important parts have trans- 
mitted themselves from Fishes up to Man, and from this 
circumstance alone it is evident how wide a chasm sepa- 
rates the Fishes from the Skull-less and Single-nostrilled 
Animals (Acraniota and Monorhina). Fishes and Man 
possess all these characters in common (Table X.). 

Turning now to consider the Fish class in greater detail, 
we may divide it primarily into three main groups, or sub- 
classes, the genealogies of which are evident. The first 
and most ancient group is that of the Primitive Fishes 
(Selachii), the best-known extant representatives of which 
are the members of the much-varied orders of Sharks and 
Rays (Figs. 191, 192). These are followed by a series of 
further developed Fish forms, < by the sub-class of Mucous 
Fishes (Ganoides). The greater number of these have long 
been extinct, and only very few living representatives are 
known ; these are the Sturgeon and Huso of European seas, 
the Polypterus of African, and the Lepidosteus and Amia 
of American rivers. The earlier abundance of forms belono^- 
ing to this interesting group is, however, proved by the 
abundance of their fossil remains. From these Mucous 
Fishes originated the third sub-class, that of the Osseous 
Fishes (Teleostei), to which belong most extant Fishes, espe- 
cially nearly all our river fish. Comparative Anatomy 
and Ontogeny very clearly show that the Ganoids sprang 
from the Selachii, just as the Teleostei sprang from the 
Ganoids. But, on the other hand, a second siJe-line, or 
rather the main ascending line of the Vertebrate tribe, 



EMBRYOS OF SHARKS 



113 




Fig. 191. 



Fig. 192, 



114 THE EVOLUTION OF MAN. 

Fig. 191. — Embryo of a Shark (Scymnus lichia), seen from ventral side ; 
V, pectoral fins (in front of these five pairs of gill-openinsfs) ; h, ventral fins ; 
a, anal opening ; s, tail fin ; k, external gill-tufts ; d, yelk-sac (the greater 
part of this has been removed) ; g, eye ; n, nose ; m, mouth fissure. 

Fig. 192. — Developed Man-shark (Carcharias melanopterus], Been from 
the left side : r^ first, r^ second dorsal fin; «, tail fin; a, anal fin; v, pectoral 
fins ; h, ventral fins. 

developed in another direction from the Primitive Fishes; 
this line leads upward through the Dipneusta group to the 
important class of Amphibia. 

This significant relationship between the three groups 
of Fishes has been placed beyond all doubt by the re- 
searches of Gegenbaur on the subject. The lucid discussion 
on the " systematic position of the Selachii " which that 
author inserted in the introduction to his classic study of 
the "head skeleton of the Selachii," must be regarded as 
definitely proving this important relation.^^^ In Primitive 
Fishes (Selachii), however, the scales (skin appendages) 
and the teeth (jaw appendages) are identical in formation 
and structure, while in the other two groups of Fishes 
(Mucous and Osseous Fishes) these organs have already 
become distinct and differentiated. Moreover, in Primitive 
Fishes, the cartilaginous skeleton (the vertebral column 
and the skull, as well as the members) is of the simplest 
and most primitive nature, of which the bony skeletons 
of Mucous and Osseous Fishes must be regarded as a 
modification. It is true that in certain respects (in the 
structure of the heart and of the intestinal canal) Mucous 
Fishes fully coincide with Primitive Fishes, and differ from 
Osseous Fishes. But a comparative review of all the 
anatomical relations plainly shows that the Mucous Fishes 
constitute a connecting group between Primitive and 



MUD-FISHES. 115 

Osseous Fishes. The Primitive Fishes (Selachii) form the 
most ancient and original group of Fishes. From these, 
in one direction, all other Fishes have developed ; the 
Mucous Fishes first, which, at a much later period (in the 
Jurassic, or the Chalk Period), gave rise to the Osseous 
Fishes. In another direction, the Primitive Fishes gave 
rise to the parent-forms of the higher Vertebrates, directly 
to the Dipneusta, and thus to Amphibians. Regarding the 
Selachii as forming the eleventh stage in our pedigree, these 
would be followed by the Dipneusta group as the twelfth 
stage, and by the Amphibian group as the thirteenth stage. 
The advance efiected in the development of the Mud- 
fishes (Dipneusta) from the Primitive Fishes is of great mo- 
ment, and is connected with a very noticeable cl^ange, which 
took place in the beginning of the Palseozoic, or Primary 
Period in organic life as a whole. For the very numerous 
fossil remains of plants and animals which are now known to 
belong to the first three epochs of the history of the earth — 
to the Laurentian, the Cambrian, and the Silurian Periods, 
are exclusively those of aquatic plants and animals. From 
this palseontological fact, taken in connection with certain 
weighty geological and biological considerations, we may 
infer, with tolerable certainty, that at that time no land- 
animals yet existed. During the whole of the enormous 
Archizoic Period — during many millions of years — the living 
population of our globe were all water-dwellers : a very 
remarkable fact, when it is remembered that this period 
embraces the larger half of the entire organic history of the 
earth. The lower animal tribes are even now exclusively, 
or with very few exceptions, aquatic. But during the 
Archizoic, or Primordial Epoch, the higher animal tribes 



Il6 THE EVOLUTION OF MAN. 

continued exclusively adapted to aquatic habits of life. It 
was not till later that they adopted a land life. The earliest 
fossils of terrestrial animals occur in the Devonian strata, 
which were deposited in the beginning of the second great 
division of the earth's history (the Palaeozoic Epoch). They 
increase greatly in number in the deposits of the Coal and 
Permian Periods. Even in these early formations many 
terrestrial and air-breathing species, both of the Arthro- 
pod and of the Vertebrate tribe, occur ; while their aquatic 
ancestors of the Silurian Period breathed nothing but 
water. * This physiologically significant modification of the 
mode of respiration is the most influential change that 
affected the animal organism in the transition from water 
to dry land. In the first place it caused the development 
of an air-breathing organ, the lung, the water-breathing 
gills having previously acted as respiratoiy organs. Simul- 
taneously, however, it efi'ected a remarkable change in the 
circulation of the blood and in the organs connected with 
this ; for these are always most closely correlated with the 
respiratory organs. In addition to these, other organs also, 
either in consequence of more remote correlation with the 
respiratory organs, or in consequence of new adaptations, 
were more or less modified. 

Within the Vertebrate tribe it was undoubtedly a branch 
of the Primitive Fishes (Selachii) which, during the De- 
vonian Period, made the first successful effort to accustom 
itself to terrestrial life and to breathe atmospheric air. In 
this the swimming-bladder was especially of service, for it 
succeeded in adapting itself to respiration of air, and so 
became a lung. The immediate consequence of this was 
fche modification of the heart and nose. While true Fishes 



EVOLUTION OF MUD-FISHES. II 7 

have only two blind nose-pits on the surface of the head, 
these now became connected with the mouth-cavity by an 
open passage. A canal formed on each side, leading directly 
from the nose-pit into the mouth-cavity, and thus even 
while the mouth-opening was closed the necessary atmo- 
spheric air could be introduced into the lungs. While, 
moreover, in all true Fishes the heart consists simply of two 
compartments, an auricle, which receives the venous blood 
from the veins of the body, and a ventricle, which forces 
this blood through an arterial expansion into the gills, the 
auricle, owing to the formation of an incomplete partition 
wall, is now divided into a right and a left half 
The riD:ht auricle alone now received the venous blood of 
the body, while the left auricle received the pulmonic 
venous blood passing from the lungs and the gills to the 
heart. The simple blood-circulation of the true Fishes thus 
became the so-called double circulation of the higher Ver- 
tebrates ; and this development resulted, in accordance with 
the laws of correlation, in further progress in the structure 
of other organs. 

The vertebrate class, which thus first adapted itself to 
the habit of breathing air, and which originated from a 
branch of the Selachii, are called Mud-fishes {Dipneusta), 
or Double-breathers, because, like the lowest Amphibia, 
they retain the earlier mode of breathing through the gills, 
in addition to the newly acquired lung-respiration. This 
class must have been represented by numerous and diverse 
genera during the Palaeolithic Epoch (during the Devonian, 
Carboniferous, and Permian Periods). As, however, the 
skeleton is soft and cartilaginous, like that of the Selachii, 
they naturally left no fossil remaina The hard teeth of 



Il8 THE EVOLUTION OF MAN. 

single genera (Ceratodus) could alone endure ; these occur, 
for instance, in the Trias. At the present time there are 
only three extant genera of this whole class : Protopterua 
annectens, in the rivers of tropical Africa (White Nile, 
Niger, Quillimane, etc.) ; Lepidosiren paraddxa, in tropical 
South America (in the tributaries of the Amazon) ; and 
Ceratodus Fosteri, in the swamps of Southern Australia 
(Plate XII.).^^^ This wide distribution of the three isolated 
descendants of the class is alone sufficient to prove that 
they are the last remnants of a group which was formerly 
very widely developed. The whole structure of their 
bodies shows that the group to which they belong forms the 
transition between Fishes and Amphibia, The direct tran- 
sitional structure between the two classes is so clearly 
expressed in the whole organization of these curious animals, 
that zoologists yet dispute whether the Dipneusta are 
Fishes or Amphibia. Some well-known zoologists still class 
them among Amphibia, while they are usually placed 
among Fishes. In fact, the characters of both the classes 
are so united in the Dipneusta that the answer to the 
question as to their nature depends entirely upon the mean- 
ing attached to the terms " Fish " and " Amphibian." In 
their mode of life they are true Amphibia. During the 
tropical winter, in the rainy season, they swim in the water 
like Fishes and inhale water through the gills. During the 
dry season they burrow in the mud as it dries up, and 
during that period breathe air through lungs, like Am- 
phibians and higher Vertebrates. In this two-fold respira- 
tion they do, it is true, coincide with the lower Amphibia, 
and stand far above Fishes. Yet, in most other characters 
they more nearly resemble the latter, and stand below the 



EXTANT MUD-FISHES. 1 19 

former. Their external appearance is entirely like that of 
Fishes. 

The head of the Dipneusta is not distinct from the 
trunk. The skin is covered with large fish-scales. The 
skeleton is soft, cartilaginous; its development has been 
arrested at a very low stage, just as in the lower Primitive 
Fishes. The notochord is retained entire. The two pairs of 
limbs are very simple fins of primitive structure, like those 
of the lowest Primitive Fishes. The structure of the braia, 
of the intestinal tube, and the sexual organs, is also as in 
Primitive Fishes. The Dipneusta, or Mud-fishes, have, there- 
fore, by heredity, accurately retained many features of a 
lower organization derived from our primseval Fish ancestors, 
while their adoption of the habit of breathing air through 
lungs introduced a great advance in the vertebrate organi- 
zation. 

Moreover, the three extant Mud-fishes differ a good deal 
from one another in important points of structure. The 
Australian Mud-fish (Ceratodus), which was first described 
at Sidney in 1870 by Gerard Kreffl, and which attains a 
length of six feet, appears in an especial degree to represent 
a primaeval and very conservative animal form (Plate XII.). 
This is especially true of the structure of its simple lung, 
and of its fins, which contain a pinnate skeleton. In the 
African Mud-fish (Protopterus), on the contrary, and in the 
American form {Lepidosiren) the double lung is present, as 
in all higher Vertebrates ; nor is the fin-skeleton pinnate. 
In addition to the internal gills, Protopterus has also ex- 
ternal gills, which are wanting in Lepidosiren. Those 
unknown Dipneusta, which were among our direct ancestors 
and which formed the connecting link between the Selachii 



( I20 ) 



TABLE XX. 

SysteiiuUic Survey of the Phyhgenetic Classification of 

Vertebrates. 



I. SkuII4ess (Acrania), or ^ubc-f)eartet( (Leptocardia). 
Vertebrates without a specialized head, skull, brain, or centralized heart. 



1. &ku\Ultss 
Aorania 



I. Tube-hearted 
Leptocardia 



1. Lancelets 



1. Amphioxida 



II. Animals hittfj skulls (Craniota) and with centraltjeti fjearts (Pachycardia). 
Vertebrates with specialized head, with skull and brain, and with a 

centralized heart. 



Main-clasiet 

of the 

Skulled Animals. 



Classes 

of the 

Skulled Aninals. 



Sub-classes 

of the 

Skulled Animal*. 



Systematic NaToe 

of the 

Sub-class€t. 



2. 5mglc= 
0ostrilktJ 
Monorhina 



3. yon« 
atnnionatt 
Anaimiia 



II. Round mouths 
Cyclostoma 

III. Fishes 
Pisces 

IV. Mud-fishes 
Dipneusta 

V. Batrachians 
Aviphihia 



k *atnnton5 
"Knimals 
Amniota 



VI. Reptiles 
Beptilia 



VII. Birds 

Aves 



VIII. Mammals 
Marrnnalia 



2. Hags, or 

Mucous Fish 

3. Lampreys 

4. Primitive Fish 

5. Ganoid Fish 

6. Osseous Fish 

7. Single-lunged 

8. Double -lunged 

9. Mailed Batra- 

chians 
10. Naked Batra- 
chians 

^IL Lizards 

12. Snakes 

13. Crocodiles 

14. Tortoises 

15. Sea -dragons 

16. Dragons 

17- FlyiugKeptiles 

18. BeakedAninials 

19. Long-tailed 

20. Fan.tailed 

21. Bush-tailed 

/22. Cloacal Animals 

23. Pouched Ani- 
mals 

24. Placental Ani- 
mals 



1 



2. Hyperotreta 
(Myxinoida) 

3. Hyperoartia 
(Petromyzontia) 

4. Selachii 

5. Ganoides 

6. Teleostei 

T.lMonopneumonee 

8. Dipneumones 

9. Phractamphibia 

10. Lissamphibia 

11. Lacertilia 

12. Ophidia 
18. Crocodilia 

14. Chelonia 

15. Halisauria 

16. Dinosauria 

17. Pterosauria 

18. Anomodonta 

19. SaururaB 

20. Carinatae 

21. Ratitas 

22. Monotrema 

23. Marsupialia 

24. Placent&lia 



Oweons fisk 
TeleoaUi 



Ganoid fish 
OanoidsM 



( 131 ) 

TABLE XXL 

Pedigree of Vertebrates. {Of. Plate XV.) 



8. fEammals 
Mammalia 



Single-lnnged 
Monop nen mones 



Double-Inn ged 
Dypneumones 



7. Birds 
Aves 

I 
6. Reptiles 

Repti/ia 



Mud -fish 
Protoptm'i 



^mnionMnimBls 
Amniota 

I 
5. ISattarfjiafts 
Ampliibia 



4. fHutJ^fisfj 
Dipneusta 



Primitive fishes Selaohii 
3. Fishes Pisces 

©oufaU^nostrillrt 
Amphirhina 



 — Lampreys Hags 

Petromytontes Myxinoid"- 



2. Round-mouths 

Cylostoina 



Sea-equirts 



Ascidico 



Sea-barrels 

Thaliacea 



IHantlcTJ ^nimali 
Tuuicata 



5>ingIf'n0striIIctJ Monorhina 
,S)kuiIrti'llutmal;a Craniota 



1. Tube-heaited 
Leptoco/rdia 



Acrania 
Vtxithxatts 
Vertebrata 



C!)ortia^^nimate 
Chordouia 



Worms 
Vermes 



122 THE EVOLUTION OF MAN. 

and the Amphibians, were doubtless in many respects 
different from their three direct descendants of the present 
time, but in the most essential characters they must have 
coincided with the latter. Unfortunately, the germ-history 
of the three surviving Mud -fishes is as yet entirely un- 
known; probably at some future time it will afford us 
further important information as to the tribal history of the 
lower Vertebrates and so of our ancestors. 

Very important information of this kind has been 
supplied by the next Vertebrate class, that of the Batra- 
chians (Amphihia), which is directly connected with the 
Dipneusta, from which it originated. To this class belong 
the Axolotl, Salamanders (Plate XIII.), Toads, and Frogs. 
Formerly, after the example of Linnaeus, all Reptiles (Lizards, 
Snakes, Crocodiles, and Tortoises) were also classed among 
Amphibia. But these animals are of a far higher organiza- 
tion, and in the most important characters of their ana- 
tomical structure are more nearly allied to Birds than to 
Amphibians. The true Amphibia, on the other hand, are 
more nearly allied to the Double-breathers and to Primitive 
Fishes : they are also much older than Reptiles. Even as 
earl}'' as the Carboniferous Period numerous very highly 
developed Amphibia (some of large size) were extant, whereas 
the earliest Reptiles first appear only towards the close of 
the Permian Period. In all probability the Amphibia were 
developed from Double-breathers at an even earlier period — 
during the Devonian Period. The extinct Amphibia, of 
which fossil remains have been preserved from that most 
ancient Primaeval Epoch — and these are especially numerous 
in the Trias — were distinguished by a large bony coat of mail 
overlying the skin (like that of the Crocodile), while most 



BATRACHIANS. I23 

of the yet extant Amphibians have a smooth and slippery 
skin. The latter, also, are on an average smoother than the 
former, and must be regarded as their stunted posterity. 

Among the Amphibia of the present time we are 
therefore, unable to find any forms that are directly referable 
tx) the pedigree of the human race, or that are to be re- 
garded as ancestors of the three higher Vertebrate classes ; 
yet, in important points of their internal anatomical struc- 
ture, and especially in their germ-development, they cor- 
respond so closely with us, that we are justified in affirming 
that between the Double-breathers (Dipneusta) on the one 
hand, and the three higher Vertebrate classes (grouped 
together as Amniota) on the other, there existed a series of 
extinct intermediate forms which, if we had them before us, 
we should class among Amphibia. The whole organization 
of the extant Amphibia represents a transitional group of 
this kind. In the important matters of respiration and 
circulation of the blood, they are still closely allied to the 
Double-breathers, although in other respects they rise above 
the latter This is especially true with respect to the ad- 
vanced structure of their limbs or extremities. The latter 
here for the first time appear as feet with five digits. The 
thorough researches of Gegenbaur have shown that the fins 
of Fishes, concerning which very en^oneous views were pre- 
viously held, are feet with numerous digits ; that is to say, 
the several cartilaginous or osseous rays, many of which occur 
in every Fish-fin, correspond to the fingers or digits on the 
limbs of higher Vertebrates. The several joints of each ray 
correspond to the several joints of each digit. In the Double- 
breathers the fin yet retains the same structure as in Fishes, 
and it was only gradually that the five-toed form of foot, 



124 THE EVOLUTION OF MAN. 

w^hich occurs for the first time in Amphibians, was developed 
from this multi -digitate form. This reduction in the numbei 
of the digits from ten to five occurred in those Dipneusta 
which must be regarded as the parent-forms of the Amphibia, 
probably as early as the latter half of the Devonian Period — 
or, at latest, in the immediately subsequent Carboniferous 
Period. Several fossil Amphibia with five digits have already 
been found in the strata of the latter period. Fossil foot- 
prints of the same animals are very numerous in the 
Trias {Cher other iun). 

The great significance of the five digits depends on the 
fact that this number has been transmitted from the 
Amphibia to all higher Vertebrates. It would be impossible 
to discover any reason why in the lowest Amphibia, as well 
as in Reptiles and in higher Vertebrates up to Man, 
there should always originally be five digits on each of the 
anterior and posterior limbs, if we denied that heredity 
from a common five-fingered parent-form is the efiicient 
cause of this phenomenon : heredity can alone account foi 
it. In many Amphibia, certainly, as well as in many higher 
Vertebrates, we find less than five digits. But in all these 
cases it can be shown that separate digits have retrograded, 
and have finally been completely lost. 

The causes which effected the development of the five- 
fingered foot of the higher Vertebrates in this Amphibian 
parent-form from the many-fingered foot, must certainly be 
found in the adaptation to the totally altered functions 
which the limbs had to discharge during the transition from 
an exclusively aquatic life to one which was partially 
terrestrial. While the many-fingered fins of the Fish had 
previously served almost exclusively to propel the body 



PINS AND FINGERS. 12$ 

through the water, they had now also to afford support to 
the animal while creeping upon land. This effected a 
modification both of the skeleton and of the muscles of 
the limbs. The number of fin rays was gradually lessened, 
and was finally reduced to five. These five remaining 
rays now, however, developed more vigorously. The soft 
cartilaginous rays became hard bones. The rest of the 
skeleton also became considerably more firm. The move- 
ments of the body became not only more vigorous, but 
also more varied. The separate portions of the skeleton 
system, and consequently those of the muscular system also, 
became more and more differentiated. Owing to the intimate 
correlation of the muscular to the nervous system, the latter 
also naturally made marked progress in point of function 
and structure. We therefore find that the brain is very 
much more developed in the higher Amphibia than in 
Fishes, in Mud-fishes, and in the lower Amphibia. 

The organs which are most modified in consequence of 
an amphibious mode of life are, as we have already seen in 
the Double-breathers (Dipneusta), those of respiration and 
of the circulation of the blood. The first advance in 
organization necessitated by the transition from aquatic to 
terrestrial habits of life was, of course, the formation of an 
air-breathing organ, a lung. This developed directly from 
the swimming-bladder which these animals had inherited 
from the Fishes. At first the function of this organ would 
be quite subordinate to the more ancient organ, used for the 
respiration of water, the gills. Hence we find that the 
lowest Amphibia, the Gilled Amphibia, like the Dipneusta, 
spend the greater part of their lives in the water, and that 
accordingly they breathe water through gills. It is only 



126 THE EVOLUTION OF MAN. 

Tor brief intervals that they rise to the surface of the water 
or creep out of the water on to the land ; and at these times 
they breathe air through lungs. Some, however, of the 
Tailed Amphibians, the Axolotl and the Salamander, live 
exclusively in the water only when young, and afterwards 
usually remain on land. In the adult state they breathe 
only air through lungs. This is also the case with the most 
highly developed Amphibians, the Frog-amphibia (Frogs and 
Toads) ; some of the latter have even entirely lost the 
gilled larval form.^^^ The same is true of a few small 
snake-like Amphibia, the Csecilise, which, like earth-worms, 
live in the ground. 

The high degree of interest attached to the natural 
history of the Amphibian class is especially due to the fact 
that they hold a position exactly intermediate between the 
higher and the lower Vertebrates. While the lower Am- 
phibia are in their whole organization directly allied to the 
Dipneusta and the Fishes, living mostly in the water and 
respiring water through gills, the higher Amphibia are no 
less directly related to the Amnion Animals, for, like the 
latter, they live mostly on land, and breathe air through 
lungs. But when young the higher forms resemble the lower, 
and only attain their own higher degree of development 
after undergoing complete modification. The individual 
germ-history of most higher Amphibians still accurately 
reproduces the tribal history of the whole class ; and the 
various stages of modification which were necessitated in 
certain low Vertebrates by the transition from aquatic to 
terrestrial habits during the Devonian or Carboniferous 
Period, are still to be seen every spring in each Frog as it 
develops from the egg in our ditches and pools. 



I 



IMPORTANCE OF AMPHIBIA. 



127 



Like the Tailed Salamanders (Fig. 193), each common 
Frog emerges from the egg in a larval form, totally different 
jccm that of the full-grown Frog (Fig. 194). The short 



I 





Fig, 193. — Larva of Spotted Land-Newt {Salamandra macuJata), from 
the ventral- Side. Li tiie centre a yelk-sac yet protrudes from the intestine. 
The external gills are prettily branched and tree-like. The two pairs of 
limbs are yet very small. 

Fig. 194. — Larva of the Common Grass-Frog (Rana temforaria) , a so- 
called tadpole : m, mouth; n, a pair of suction cups used in clinging to stones; 
d, skin-fold, which gives rise to the gill-roof ; behind are the gill-openings, 
from which the gill branches protrude ; s, tail-muscles ; /, skin-fold of the 
tail, forming a float. 

■s 

irunk is produced into a long tail, which in form and struc- 
42 



125 THE EVOLUTION OF MAM. 

ture reseml:)les the tail of a Fish (s). At first it has no 
limbs. Respiration is accomplished solely by gills, which 
are at first external (k) and afterwards internal. Corre- 
spo'ndingly, the heart is also of the same form as in the 
Fishes, and consists of only two compartments — an auricle, 
which receives the venous blood of the body, and a ven- 
tricle, which drives it through the arterial bulb into the 
gills. 

Numbers of these fish-like Frog larvae, or " tadpoles," as 
they are called, swim about every spring in all ponds and 
pools, using their muscular tails for propulsion, just as is 
done by Fishes and larval Ascidians. The remarkable 
transformation of the fish-like form into that of the Froji 
does not take place till after the tadpole has grown to n 
certain size. From the throat grows a closed sac which 
develops into a pair of large sacs; these are the lungs. 
The simple chamber of the heart is divided into two auricles, 
owing to the formation of a partition wall, and simul- 
taneously considerable changes of structure occur in the 
main arterial trunks. Previously all the blood passed from 
the heart-chamber through the aorta arches into the gills ; 
but only part of it now passes to the gills, while another 
part passes thiough the newly formed lung arteries into the 
lungs. From the lungs arterial blood returns into the left 
auricle of the heart, while the venous blood of the body 
collects in the right auricle. As both of the auricles open 
into the simple ventricle, the latter contains mixed blood. 
The fish-like form has now passed into the Dipneusta form. 
During the further course of modification the gills, with 
the gill- vessels, are entirely lost, and respiration is now pei- 
formed by the lungs alone. Yet later, the long tail is also 



GILLED BATRACHIANS. 1 29 

rejected, and the Frog now leaps about on the land on legs 
which have sprouted in the mean time.^^ 

This remarkable metamorphosis of the higher Amphibia 
ia very instructive in its bearing on Man's ancestral history, 
and is especially interesting owing to the fact that the 
various groups of extant Amphibia have remained stationary 
at various stages of their tribal history, which, in accord- 
ance with the fundamental law of Biogeny, are reproduced 
in this germ-history. First, there is a very low order of 
Amphibia, the Gilled Batrachians {Sozohranchia), which, like 
Fishes, retain their gills throughout life. To this order 
belong, among others, the well-known blind " 01m " of the 
Adelsberg Cave {Proteus anguineus), the Mud-eel of South 
Carolina {Siren lacertina), and the Axolotl of Mexico (Sire- 
don pisciformiis ; Plate XIII. Fig. 1). All these Gilled 
Batrachians are fish-like animals with long tails, and in 
point of respiratory organs and of circulation of the blood 
they remain throughout life stationary at the Dipneusta 
stage. They possess both gills and lungs, and can either 
respire water through the gills or air through the lungs, as 
occasion requires. In another order, the Salamanders, the 
gills are lost during metamorphosis, and in the adult state air 
only is breathed through lungs. This order bears the name 
of Tailed Batrachians {Sozura) because they retain the tail 
throughout life. To this order belong the common Water- 
Newts \Triton) which swarm in all ponds during the 
summer, and the black, yeUow-speckled Land-Salamanders 
(Saiamandra) foiuad in damp woods (Plate XIII. Fig. 2). 
The latter are among the moat remarkable of our indigenous 
animals, sundry anatomical characters proving them to bo 
very ancient and highly conservative Vertebrates.^^ A 



130 THE EVOLUTION OF MAN. 

few Tailed Batrachians retain the gill-opening in the side 
of the neck, though the gills themselves are lost {Meno- 
poma). If the larv?e of the Salamanders (Fig. 193) and 
Tritons are compelled to remain in water, and not allowed 
to get on land, they may, under favourable conditions, be 
made to retain their gills. In this fish-like condition they 
become sexually mature, and will throughout life remain 
compulsorily in the lower stage of development of the 
Gilled Batrachians. The opposite experiment was made 
some years ago in the case of the Mexican Gilled Batra- 
chian, the fish-like AxolotJ (Siredon pisciformis; Plate 
XIII. Fig. 1). This animal had previously been regarded 
as a permanent Gilled Batrachian, remaining throughout 
life in this fish-like condition. But of the hundreds of 
these animals kept in the Jardin des Plantes at Paris, a few 
individuals, for some unknown reason, crept to land, lost 
their gills, and changed into a form closely allied to that of 
the Salamander (Amhlystoma, Fig. 2). In this state they 
became sexually mature.^^^ This phenomenon, which at 
first excited a lively interest, has since been repeatedly 
observed with care. Zoologists regarded the fact as some- 
thing peculiarly wonderful, though each spring every 
common Frog and Salamander passes through the same 
modification. In these animals we can in the same way 
follow each step in the significant metamorphosis of the 
aquatic and gill-respiring animal into the terrestrial and 
lung-respiring animal. That which thus takes place in the 
individual during germ-evolution, took place in the same 
way in the whole class during the course of its tribal 
history. 

The metamorphosis which takes place in the third order 



HAECKRL S EVOLUTION OF MAN. 



PLATE XII. 



'm 



t^>ii 



i 



m 









Tigl 



^m^^ 



liS^ 



/" 






X 



If 



A/ 



x.\' 



J/, 



-^\ 



(>« 



j([i 



>'-i 



S^ 



Cera^odus 
Torsteri 



^j 



'^»^ 



vS*s 



HA.ECKEL S EVOLUTION OF MAN 



PLATE XIII. 




f^2 






\i\ 



■•j^-^^' 
:?"% 



m^ 






Fig. I. Siredon pisciformis. 



Fig. 2. Salamandra maculata. 



TAILED BATRACHIANS AND FROG BATRACHIANS. I31 

of Amphibia, the Frog Batrachians (Batrachia, or Anura), 
is yet more complete than in the Salamanders. To these 
belong all the various kinds of Toads, Water-frogs, Tree- 
frogs, etc. In the course of transformation these lose not 
only the gills, but also the tail, which drops off in some 
cases earlier, in others later. In this respect the various 
species differ somewhat from one another. In most Frog 
Batrachians the larvae drop the tail very early, and the 
tail-less frog-like form subsequently grows considerably 
larger. Other species, on the contrary, as, for instance, the 
Pseudes paradoxus of Brazil, as also an European Toad (Pelo- 
hatesfuscus) remain for a very long time in the fish fonn, 
and retain a lengthy tail till they have almost attained 
their full size; hence, after their metamorphosis is com- 
pleted, they appear much smaller than before. The opposite 
extreme is seen in some Frogs but recently brought under 
notice, which have lost the whole of their historic meta- 
morphoses, and in which no tailed and gilled larva emerges 
from the egg, but the perfect Frog, without tail or gills. 
These Frogs inhabit isolated oceanic islands, the climate 
of which is very dry, and which are often for a con- 
siderable leno-th of time without fresh water. As fresh 
water is indispensable for gill-respiring tadpoles, these Frog- 
have adapted themselves to this local deficiency and have 
entirely relinquished their original metamorphosis, e.g.. 
Hylodes martinicensis}^ 

The ontooenetic loss of o'ills and tail in Frosts and Toads 
can of course only be phylogenetically explained as owing 
to the fact that these animals have descended from long- 
tailed salamander-like Amphibians. This is also proved 
beyond doubt by the Comparative Anatomy of the two 



132 THE EVOLUTION OF MAN. 

^oups. This remarkable transformation is, in other res\ ecta 
also, of general interest, as throwing a flood of light upon the 
Phylogeny of the Tail-less Apes and of Man. Man's ances- 
tors were also long-tailed gill- breathing animals, resembling 
Gilled Batrachians, as is irrefutably demonstrated by the 
tail and the gill arches in the human embryo. 

During the Palgeozoic Epoch, and probably in the Car- 
boniferous Period, there is no doubt that the Amphibian 
class embraced a series of forms which must be regarded as 
direct ancestors of Mammals, and so of Man. On grounds 
derived from Comparative Anatomy and Ontogeny, we must 
not, however, look for these Amphibian ancestors of ours — 
as might perhaps be supposed — among the Tail-less Frog 
Batrachians, but only among the lower Tailed Amphibians. 
We can with certainty point to at least two extinct Batra- 
chian forms as direct ancestors of Man, as the thirteenth 
and fourteenth stages in our pedigree. The thirteenth 
ancestral form must have been closely allied to the Double- 
breathers (Dipneusta), must, like these, have possessed per- 
manent gills, but must have been already characterized by 
having five digits on each foot ; and were they still living we 
should place them in the group of Gilled Batrachians, with 
the Proteus and the Axolotl (Plate XIII. Fig. 1). The 
fourteenth ancestral form, on the other hand, must indeed 
have retained the long tail, but must have lost the gills, and 
hence the nearest aUied forms among extant Tailed Batra- 
chians would be the Water-Newts and Salamanders 
(Plate XIII. Fig. 2). Indeed, in the year 1725 the fossil 
skeleton of one of these extinct Salamanders (closely aUieJ 
to the present giant Salamander of Japan) was described 
by the Swiss naturalist, Scheuchzer, as the skeleton of 



PRIMITIVE AMNION ANIMALS. 1 33 

a fossil Man dating from the Deluge ! (" Homo diluvii 
testis." i«^) 

As the vertebrate form occurring in our pedigree imme- 
diately after these Batrachian ancestors — and, therefore, as 
the fifteenth stage — let us now examine a lizard-like animal, 
^ which no fossil remains have been obtained, and which 
k not even proximately represented in any extant animal 
form, but the former existence of which we may infer with 
the utmost certainty from certain comparative anatomical 
and ontogenetica] facts. This important animal form we 
will call the Protamnion, or Primitive Amniotic animal. 
All Vertebrates higher than the Amphibia — that is, the three 
classes of Reptiles, Birds, and Mammals — are so essentially 
distinct in their whole structure from all the lower Verte- 
brates which we have as yet considered, and, on the other 
hand, have so much in common, that we may class tlienj 
together in one group as Amnion Animals {Arriniota). It it 
only in these three classes of animals that we find that 
remarkable envelope of the embryo known as the amnion. 
(Cf. vol. i. p. 386.) The latter must probably be regarded as 
a kenogenetic adaptation, as caused by the sinking of the 
embryo into the yelk-sac.^^^ 

All known Amnion Animals, all Reptiles, Birds, and 
Mammals (Man included), coincide in so many important 
points of organization and development that we are fully 
justified in asserting their common descent from a single 
parent form. If the testimony of Comparative Anatomy 
and Ontogeny is entirely unquestionable in any point, it is 
certainly so here. For all the special peculiarities and 
characters, which appear accompanying and following the 
formation of the amnion; and which we found in the 



134 THE EVOLUTION OF MAH. 

development of the human embryo; all the many peculiari- 
ties in the development of the organs which we shall 
presently notice in detail ; and, finally, the chief special 
arrangements of the internal structure of the body in all 
fully developed Amnion Animals; all these so clearly demon- 
strate the common origin of all Amnion Animals from a 
single extinct parent-form, that it is impossible to conceive 
their origin as polyphyletic, and that they originated from 
several independent parent- forms. This unknown common 
parent-form is the Primitive Amnion Animal {Protam- 
nion). ' In external appearance the Protamnion was most 
probably an intermediate form between the Salamanders 
and the Lizards. 

It was probably during the Permian Period that the 
Protamnion originated ; perhaps at the beginning, perhaps 
at the close of that period. This we know from the fact 
that the Amphibia did not attain their full development till 
the Carboniferous Period, and that toward the close of the 
Permian the first fossil Reptiles make their appearance — 
or, at least, fossils (Proterosaurus, Phopalodon) which must 
in all probability be referred to lizard-like Reptiles. Among 
the great and pregnant modifications of the vertebrate 
organization determined during this period by the develop- 
ment of the first Amnion Animals from salamander-like 
Amphibians, the three following are especially important : 
the total loss of water-breathing gills and modification of 
the gill-arches into other organs ; the formation of the 
allantois, or primitive urinary sac ; and, finally, the develop- 
ment of the amnion. 

The total loss of the respiratory gills must be regarded 
as one of the most prominent characters of all Amnion 



BYOLUTION OF AMNION ANIMALS. I35 

1 

Animals. All these, even such as live in the water, e.g. 
whales, respire only air through lungs, never water through 
gills. While all Amphibians, with very few exceptions, in 
the young state retain their gills for a longer or shorter 
period, and breathe through gills for some time (if not 
always), from this point gill-respiration entirely ceases. 
Even the Protamnion must have entirely ceased to breathe 
water. The gill-arches, however, remain, and develoji 
into very different organs (partly rudimentary) ; into the 
various parts of the tongue-bone, into certain portions of the 
jaw apparatus, the organ of hearing, etc. But no trace oj 
gill-leaves, of real respiratory organs on the gill-arches, are 
ever found in the embrvo of Amnion Animals. 

With this total loss of the gills is probably connected 
the formation of another organ, which we have akead} 
described as occurring in human Ontogeny ; this is the 
allantois, or primitive urinary sac. (See vol. i. p. 379.) In 
all probability the urinary bladder of the Dipneusta is to be 
regarded as the first beginning of the allantois. Even in 
the American Mud-fish {Lepidosiven) we find an urinary 
bladder, which grows from the lower wall of the posterior 
extremity of the intestine, and serves as a receptacle for 
the renal secretions. This organ has been inherited by the 
Amphibia, as may be seen in any Frog. But it is only in 
the three higher Vertebrate classes that the allantois attains 
a special development ; in these it protrudes at an early 
period from the body of the embryo, forming a large sac 
filled with liquid, and traversed by a considerable number 
of large blood-vessels. This sac also discharges a portion of 
the nutritive functions. In the higher Mammals and in 
Man the allantois afterwards forms the placenta. 



1^6 THE EVOLUTION OF MAN. 

The formation of the amnion and the allantois, together 
with the total loss of the gills and the exclusive adoption 
of lung-respiration, are the most important characters by 
which all Amnion Animals are distinguished from the lower 
Vertebrates which we have been considerinor. In addition 
to these there are a few subordinate characters which are 
constantly inherited by Amnion Animals, and are altogether 
wanting in animals without an amnion. One striking em- 
bryonic character of the Amnion Animals is the great curva- 
ture of the head and neck of the embryo. In the Anamnia 
the embryo is from the first either nearly straight, or else 
the whole body is bent in a sickle-shaped curve corre- 
sponding to the curvature of the yelk sac, to which the 
embryo is attached by its ventral surface ; but there are 
no marked angles in the longitudinal axis (Plate VI. 
Fig. F). In all Amnion Animals, on the contrary, the 
body is very noticeably bent at an early age, so that the 
back of the embryo is much arched outwards, the head 
pressed almost at right angles against the breast, and the 
tail inclined on to the abdomen. The tail extremity, as it 
bends inwards, approaches so near to the frontal side of 
the head, that the two often nearly touch (Plates VI, and 
VII.). This striking triple curvature of the embryonic 
body, which has already been considered when we studied 
the Ontogeny of ^lan, and in which we distinguished the 
skull-curve, neck-curve, and tail-curve (vol. i. p. 871), is a 
characteristic peculiarity common to the embryos of all 
Reptiles, Birds, and Mammals. But in the formation of man)» 
internal organs also, an advance is observable in all the 
Amnion Animals which ranks them above the highest of 
the non-aronionate forms. Above all, a partition wall foims 



MAN AS AN AMNION ANIMAL. 1 37 

within the simple ventricle of the heart, dividing it into a 
right and a left ventricle. In connection with the complete 
metamoi^hosis of the gill-arches, a further development of 
the organ of hearing takes place. A considerable advance 
is also noticeable in the development of the brain, the skele- 
ton, the muscular system, and other parts. Finally, the 
reconstruction of the kidneys must be regarded as a mdst 
important modification. In all the lower Vertebrates as yet 
considered, we have found the primitive kidneys, which 
appear very early in the embryos of aU higher Vertebrates 
up to Man, acting as a secretory or urinary apparatus. In 
Amnion Animals, however, these early primitive kidneys 
lose their function at an early period of embryonic life, and 
it is assumed by the permanent " secondary kidneys," which 
grow out of the terminal portion of the primitive kidney 
ducts. 

Looking: back at the whole of these characters of Amnion 
Animals, it is impossible to doubt that all animals of this 
group, all Reptiles, Birds, and Mammals, had a common 
origin, and constitute a single main division of kindred 
forms. To this division belongs our own race. In his 
whole organization and germ-history Man is a true Amnion 
Animal, and, in common with all other Amniota, has 
descended from the Protamnion. Although this whole 
group originated at the end, or perhaps even in the middle, 
of the Palseozoic Epoch, it did not attain its full de- 
velopment and its full perfection till the Mesozoic Epoch. 
The two classes of Birds and Mammals then first appeared. 
Nor did the Reptilian class develop in its fuU variety 
until the Mesozoic Epoch, which is, therefore, called the "Age 
of Reptiles." The unknown and extinct Protamnion, the 



138 THE EV0LT7TI0N OF MAN. 

parent-form of iue entire group, must have been very nearly 
allied to the Reptiles in its whole organization, even though 
it cannot be regarded as a true Reptile in the present 
meaning of the term. Of all known Reptiles, certain Lizards 
are most nearly allied to the Protamnion ; and in the 
outward form of its body we may imagine the latter as 
an intermediate form between the Salamander and the 
Lizard.^^ 

The Comparative Anatomy and Ontogeny of the Am- 
nionate group clearly explains its genealogy. The gi*oup 
which directly descended from Protamnion gave rise to two 
divergent branches. The first of these, which will in future 
receive our whole attention, forms the Mammalian group. 
The other branch, which assumed an entirely different course 
of progressive development, and which is connected with 
the mammalian branch only as the root, is the compre- 
hensive group constituted by Reptiles and Birds. The two 
latter forms may be classed together as Monocondylia, or 
SauTopsides. The common parent-form of these is an 
extinct lizard-like Reptile. From this, the Serpents, Croco- 
diles, Tortoises, Dragons, etc. — in short, all the various forms 
of the Reptilian gi'oup — developed in different directions. 
The remarkable group formed by the Birds also developed 
directly from an offshoot of the Reptilian group, as is now 
definitely proved. Down to a late time the embryos of 
Reptiles and of Birds are yet identical, and even later they 
are in some respects surprisingly similar. (See Plate VI. Fig. 
T and C.) In their entire organization the resemblance 
between the two is so great that ^o anatomist now denies 
that the Birds originated from Reptiles. The Mammalian 
line is connected at its roots with the Reptilian line but 



GENEALOGY OF AMNION ANIMALS. 1 39 

afterwards diverged entirely from the latter, and developed 
in an entirely peculiar direction. The highest result of the 
development of the Mammalian line is Man, the so-called 
" Crown of Creation.** 



CHAPTER XIX. 

THE PEDIGREE OF MAN. 

IV. Feom the Primitive Mammal to the Ape. 

The Mammalian Character of Man. — Common Descent of all Mainmalb 
from a Single Parent-form (Promammalian). — Bifurcation of the Am 
nion Animals into Two Main Lines : on the one side, Reptiles and Birds, 
on the other. Mammals. — Date of the Origin of Mammals : the Trias 
Period. — The Three Main Groups or Sub-classes of Mammals : their 
Genealogical Relations. — Sixteenth Ancestral -Stage: Cloacal Animals 
(Monotremata, or Ornithodelphia) . — 'Ihe Extinct Primitive Mammals 
(^Promammalia) and the Extant Beaked Animals {Ornitho stoma) . — 
Seventeenth Ancestral Stage : Pouched Animals {Marsupialia, or Didel- 
phia). — Extinct and Extant Pouched Animals. — Their Intermediate 
Position between Monotremes and Placental Animals. — Origin and 
Structtire of Placental Animals {Placentalia, or Monodelphia) . — Forma- 
tion of the Placenta. — The Deciduous Embryonic Membrane (Decidua). 
— Group of the Indecidua and of the BecidMata. — The Formation of the 
Decidua {vera, serotina, rejlexa) in Man and in Apes. — Eighteenth 
Stage: Semi-apes {Prosimice) . — Nineteenth Stage : Tailed Apes {Meno' 
eerca). — Twentieth Stage : Man-like Apes (Anthropoides). — Speechless 
and Speaking Men {Mali. Homines). 

** A century of anatomical research brings ns back to the conolnsion of 
Linnaeus, the great lawgiver of systematic zoology, that man is a member 
of the same order as the apes and lemurs. Perhaps no order of mammals 
presents us with so extraordinary a series of gradations as this, leading us 
insensibly from the crown and summit of the animal creation down to 
creatures from which there is but a step, as it seems, to the lowest, smallest, 
»ixd least intelligent of the placental mammalia. It is as if nature iierself 



"man's place in nature." 141 

had foreseen the axrogance of man, and with Roman Beverity had provided 
that his intellect, by its very tnumphs, should call iuto {n'ominence the 
slaves, admonishing the conqueror that he is but dust." — Thomas Huxlev 
(1863). 

Among those zoological facts which afford us points of 
support in researches into the pedigree of the human race, 
the position of Man in the Mammalian class is one of the 
most important and fundamental. Much as zoologists havr 
long disagreed in their opinions as to Man's particular place 
 in this class, and especially in their ideas of his relation to 
the most nearly related group, that of the Apes, yet no 
naturalist has ever doubted that Man is a genuine Mammal 
in the whole structure and development of his body. Every 
anatomical museum, every manual of Comparative Anatomy, 
affords proof that the structure of the human body shares 
all those peculiarities which are common to all ^Lammals, 
and by which the latter are definitely distinguished from all 
other animals. 

Now, if we examine this established anatomical fact 
phylogenetically, and in the light of the Theory of Descent, 
we arrive immediately at the conclusion that Man is of a 
common stock with all the other Mammals, and springs 
from a root common to them. The various characteristics 
in which all Mammals coincide, and in which they diffei 
from all other animals, are, moreover, of such a kind, that a 
polyphyletic hypothesis appears in a special degree inad- 
missible in their case. It is inconceivable that all existing 
and extinct Mammals have sprung from several ditlerent 
and originally separate root-forms. We are compelled, if 
we in any way acknowledge the Theory of Evolution, to 
assume the monophyletic hypothesis, that all Mammals, 



142 THE EVOLUTION OF MAN. 

including Man, must be traced from a single common mam- 
malian parent-form. This long extinct primaeval root-form 
and its immediate descendants — which differ from each 
other hardly more than do several species of one genus — we 
will call Primitive Mammals (Promarrinialia). As we have 
already seen, this root-form developed from the ancient 
parent-form of the Primitive Amnion Animals in a direction 
wholly different from that followed by the Reptile group, 
which afterwards gave rise to the more highly developed 
class of Birds. The differences which distinguish Mammals 
on the one side, from Reptiles and Birds on the other, are so 
important and characteristic, that we may quite safely as- 
sume a bifurcation of this kind in the vertebrate family tree. 
Reptiles and Birds — which we classed together as Monocon- 
dylia, or Sauropsida — coincide entirely, for instance, in the 
characteristic structure of the skull and brain, which is 
strikingly dissimilar from that of the same parts in Mam- 
mals. In Reptiles and Birds, the skull is connected with the 
first cervical vertebra (the atlas) by a single joint-process 
(condyle) of the occipital bone; in Mammals, on the con- 
trary (as in Amphibians), the condyle is double. In the 
former, the under jaw is composed of many parts, and is 
connected with the skull by a peculiar bone of the jaw 
(the square bone) so as to be movable ; in the latter, on the 
contrary, the lower jaw consists of but two bone-pieces, 
which are directly attached to the temporal bone. Again, 
the skin of the Sauropsida (Reptiles and Birds) is covered 
with scales or feathers, that of the Mammals with hair. 
The red blood-cells of the former are nucleated, those of the 
latter non-nucleated. The eggs of the former are very 
large, are provided with a large nutritive yelk, and undergo 



REPTILES AND MAMMALS. 143 

discoidal cleavage resulting in a Disc-gastrula ; the eggs of 
the latter are very small, and their unequal cleavage results 
in the formation of a Hood -gas trula. Finally, two charac- 
ters entirely peculiar to Mammals, and by which these 
are distinguished both from Birds and Reptiles and from all 
other animals, are the presence of a complete diaphragm, 
and of the milk-glands (manionce), by means of which the 
new-bom young are nourished by the milk of the mother. 
It is only in Mammals that the diaphragm forms a transverse 
partition- wall across the body-cavity (coeloma), completely 
separating the chest from the ventral cavity. (Cf. Plate V. 
Fig. 16 z.) It is only among Mammals that the mother 
nourishes the young with her milk ; and the whole class are 
well named from this. 

These important facts in Comparative Anatomy and 
Ontogeny clearly show that the tribe of Amnion Animals 
(Amniota) bifurcated from the very first into two main 
diverging lines ; on the one side, the Reptilian line, from 
which the Birds afterwards developed ; on the other side, 
the Mammalian line. The same facts also prove as indu- 
bitably that Man originated from the latter line. For Man, 
in common with Mammals, shares all the characteristics we 
have mentioned, and is distinguished by them from aF 
other animals. And, finally, these facts indicate as ceii^inly 
those advances in vertebrate structure by which one branch 
of the Primitive Amnion Animals developed into the parent- 
form of Mammals. The most prominent of these advances 
were (1) the characteristic modification of the skull and 
brain ; (2) the formation of a covering of hair ; (3) the com- 
plete development of the diaphragm ; and (4) the formation 

of the milk-ijlands and the adaptation to the suckling of 
43 



144 THE EVOLUTION OF MAN. 

the young. Intimately connected with these, other im- 
portant structural modifications gradually occurred. 

The period at which these important advances, which 
laid the first foundation of the Mammalian class, took place, 
may most probably be placed in the first part of the 
Mesolithic, or Secondary Epoch, in the Triassic Period. 
For the oldest known fossil remains of Mammals occur in 
sedimentary rock -strata of the most recent deposits of the 
Triassic Period, in the upper Keuper. It is possible, 
indeed, that the parent-forms of Mammals may have 
appeared earlier (perhaps even at the close of the Palajo- 
lithic Epoch, in the Permian Period). But no fossil remains 
of Mammals belonging to that period are as yet known. 
Throughout the Mesolithic Epoch, throughout the Triassic, 
Jurassic, and Calcareous Periods, fossil remains of Mammals 
are very scarce, and indicate a very limited development 
of the whole class. During this Mesolithic Epoch, Reptiles 
play the chief part, and Mammals are of quite secondary 
importance. It is, however, especially significant and 
interesting, that all mammalian fossil remains of the 
Mesozoic Epoch belong to the older and inferior division 
of Pouched Animals {Marsupialia), a few probably even 
to the yet older division of the Gloacal Animals (Mono- 
trema). Among them, no traces of the third and most 
highly developed division of the Mammals, the Placental 
Animals, have as yet boen found. The last, to which Man 
belongs are much more recent, and their fossil remains do 
not occur till much later — in the succeeding Csenolithic 
Epoch ; in the Tertiary Period. This palseontological fact 
is very significant, because it harmonizes perfectly with 
that order of the development of Mammals which is un- 



THE THREE MAMMALIAN GROUPa 1 45 

rnistakably indicated by Comparative Anatomy and Onto- 
geny. 

These show that the whole Mammalian class is divisible 
into three main groups, or sub-classes, corresponding to 
three successive stages of phylogenetic evolution. These 
three stages which consequently represent three important 
ancestral stages in the human pedigree, were first dis- 
tinguished in the year 1816 by the celebrated French 
zoologist, Blainville, who named them, according to the 
difierent structure of the female organs of re {production, 
Orniiliodelphia, Didelphia, and Monodelphia {^eX<pvg, 
which, being interpreted, is uterus). It is not, however, 
only in the varied structure of the sexual organs that these 
three classes differ from one another, but in many other 
respects also, so that we can safely maintain the important 
phylogenetic statement : The Monodxlphia, or Placental 
Animals, have descended from the Dldelphia, or Pouched 
Animals; and the latter, again, have descended from the 
Cloacal Animals, or Oriiithodelphia.^ 

Accordingly we have now to consider, as the sixteenth 
ancestral stage in the human pedigree, the oldest and lowest 
main group of Mammals ; the sub-class of the Cloacal 
Animals (Monotremata, or Ornithodelphia). They are so 
named in consequence of the cloaca, which they have in 
common with the other lower Vertebrates. This so-called 
cloaca is the common excretory channel for the excrement, 
the urine, and the sexual products (Fig. 827). For, in 
these Cloacal Animals, the urinary duct and the sexual 
canals yet open into the posterior parts of the intestine, 
while in all other Mammals they are wholly separated from 
the rectum and anus, and open by a special orifice (porus 



146 THE EVOLUTION OF MAN. 

urogenitalis). The urinary bladder in the Monotreines also 
opens into the cloaca, and is separate from the two urinary 
ducts (Fig. 327, vo) ; in all other Mammals the .atter open 
directly into the urinary bladder. The structure of the 
milk -glands, by means of which all Mammals suckle their 
new-born young for a time, is also quite peculiar in 
the Cloacal Animals. In them the milk gland has no 
nipple which the young animal can suck ; there is only 
a peculiar sieve-like place in the skin, perforated with 
holes through which the milk passes out, and from which 
the young animal has to lick it. For this reason they 
have also been called Nipple-less Mammals {Amasta). 
Again, the brain of the Cloacal Animals has remained at a 
much lower stage of development than that of any other 
Mammal. The fore-brain, or cerebrum, is so small that 
it does not overhang the hind- brain, or cerebellum. In the 
skeleton (Fig. 196), the structure of the shoulder girdle, as 
well as of other parts, is remarkable, differing entirely from 
the same part in other Mammals, and resembling rather 
those of the lower Vertebrates, especially Reptiles and 
Amphibians. Like the latter, the Cloacal Animals have a 
well-developed coracoid bone (coracoideuTri), a strong bone 
uniting the shoulder-blade with the breast-bone. In all 
other Mammals the coracoid bone (as in Man) has degene- 
rated, has coalesced with the should er-blade, and appears 
only as an insignificant process of the latter. These and 
many other less striking peculiarities prove beyond doubt 
that the Cloacal Animals occupy the lowest rank among 
Mammals, and represent a direct intermediate form between 
the Protamnia and other Mammals All these marked Am- 
[)hibian characters must have been present in the parent 



EXTANT CLOACAL ANIMALS. 1 47 

form of the whole vertebrate class, in the Primitive 
Mammal, by which they must have been inherited from 
the Primitive Amnion Animals. 

During the Triassic and Jurassic Periods, the sub-class 
of the Cloacal Animals seems to have been represented by 
many Primitive Mammals of very varied form. At present 
it is represented only by two isolated members, which 
are gi'ouped together as the Beaked Animal family (Orni- 
thostoma). Both of these are confined to Australia and the 
neighbouring island of Van Diemen's Land, or Tasmania ; 
both are becoming less numerous year by year, and will 
soon be classed, with all their blood relations, among the 
extinct animals of our globe. One of these forms passes 
its life swimming about in rivers, and builds subterranean 
dwellings on the banks : this is the well-known Duck- 
billed Platypus {0r7iithorJiynchus paradoxus) : it is web- 
footed, has a thick, soft skin, and broad, flat jaws, which 
very much resemble a duck's bill (Figs. 195, 196). The 
other form, the Porcupine Ant-eater (Echidna hystrix), much 
resembles the Ant-eaters, in its mode of life, in the cha- 
racteristic form of its slender snout, and in the great length 
of its tongue ; it is covered with prickles, and can roll itseK 
up into a ball like a hedgehog. Neither of these extant 
Beaked Animals possesses true bony teeth, and, in this 
point, they resemble the Toothless Mammals (Edentata). 
The absence of teeth, together with other peculiarities of 
the Ornithostomata, is probably the result of comparatively 
recent adaptation. Those extinct Cloacal Anima's which 
embraced the parent-forms of the whole Mammalian class, 
the Promammalia, must certainly have been provided with 
a developed set of teeth, inherited from Fishes.-^^' Some 



148 



THE EVOLUTION OF MAN. 




Fig. 195.— The Duck-billed Platy- 
pus (Ornitliorhynchus paradoxus). 
Fig. 193.— Skeleton of Platypus. 




POUCHED ANBIALS. I49 

Bmall single molars, found in the uppermost strata of 
the Keuper formation in England and Wiirtemberg, and 
which are the oldest known vertebrate remains, probably 
belong to these primseval Promammalia. These teeth, by 
their form, indicate species that lived on insects ; the species 
lias been called Microlestes antiqitus. Teeth belonging to 
another closely allied Primitive Mammal (Dromatheriuni 
sUvestre) have recently been discovered in the Nortli 
American Trias. 

On the one hand, the still extant Beaked Animals, and, on 
the other, the parent-forms of the Pouched Animals {Mar- 
supialia, or Didelphia), must be regarded as represent! n<: 
two distinct and divergent lines of descent from the Pro 
mammalia. This second Mammalian sub-class is ver} 
interesting as a perfect link between the two other sub- 
classes. While the Pouched Animals, on the one side, retain 
many of the characters of the Cloacal Animals, they also, 
on the other, possess many placental characters. A few 
characters are quite peculiar to Pouched Animals alone . 
such, for instance, is the structure of the male and female 
sexual organs, and the form of the lower jaw The dis- 
tinctive feature of the latter in these Pouched Animals is a 
peculiar hook-shaped bony process, passing inward hori- 
zontally from the angle of the lower jaw. As neither 
Cloacal Animals nor Placental Animals have this process, 
tiiis structure is alone sufficient to distinguish the Pouched 
Animals (Marsupialia). Nearly all the known mammalian 
fossils from the Jurassic and Cretaceous formation are lower 
jaws. Our whole knowledge of numerous mesolithic mam- 
malia, the former existence of which would otherwise never 
have been known, is solely derived from their fossilized 



ISO THE EVOLUTION OF MAN. 

lower jaws, no fragment of the rest of their bodies having 
been reserved. According to the logic usually applied to 
palaeontology by the " exact " opponents of the theory of 
evolution, the inference drawn from this fact would be 
that these Mammals had no bones except lower jaws. The 
remarkable circumstance is, after all, very easily accounted 
for. The lower jaw of Mammals being a solid and excep- 
tionally hard bone, but very loosely attached to the skull, it 
is easily detached from the carcase as the latter is carried 
down by some river, and, falling to the bottom, is retained 
in the mud. The rest of the carcase is carried on further, 
and is gradually destroyed. As all the mammalian lower 
jaws found, in England, in the Jurassic strata of Stonesfield 
and Purbeck, exhibit this peculiar process characteristic of 
the Pouched Animals {Marsupialia), we may infer, from 
this palaeontological fact, that they belonged to Marsupials. 
No Placental Animals appear to have existed during the 
Mesolithic Epoch. At least no fossil remains, undoubtedly 
belonging to these and dating from that epoch, are known. 

The extant Pouched Animals, the most generally known 
of which are the gramnivorous Kangaroos and the carni- 
vorous Pouched Rats, display very considerable difference in 
their organization, in the form of their bodies and in size, 
and in many respects correspond to the several orders of 
Placental Animals. The great majority of them live in 
Australia, in New Holland, and in a few of the Australian 
and South Asiatic islands ; some few species occur in 
America. On the other hand, there is no longer a single 
indigenous Pouched Animal on the continents of Asia, of 
Africa, or of Europe. The case was very different during the 
Mesolithic, and also during the earlier Csenolithic Epochs. 



EXTANT POUCHED ANIMALS. 15 1 

The Neptunian deposits of these epochs in all quarters of 
the globe, and even ui Europe, contain abundant marsupial 
remains in great variety, some of them being of very large 
size. From this we ma} infer that the extant Pouched 
Animal? are but the last remnant of a group which was 
once much more widely developed, and which was dis- 
tributed over the whole surface of the globe. During the 
Tertiary Period, these succumbed in the struggle for life 
with the stronger Placental Animals, and the sur\dvors were 
gradually driven back by the latter into their present 
restricted area. 

From the Comparative Anatomy of the extant Pouched 
Animals, very important conclusions may be drawn as to 
their phylogenetic intermediate position between Cloacal 
Animals and Placental Animals. The incomplete develop- 
ment of the brain, especially of the fore-brain (cerebrum), 
the possession of marsupial bones (ossa marsupialia), the 
simple structure of the allantois (which does not as yet 
develop a placenta), with many other characters, have been 
inherited by the Pouched Animals from Cloacal Animals. 
On the other hand, they have lost the independent coracoid 
bone (o8 coracoideum) attached to the shoulder girdle. A 
more important step consists in the fact that a cloaca is no 
longer formed ; the cavity of the rectum, together with the 
anal opening, is separated by a partition wall from the urinary 
and sexual opening (sinus urogenitalis). Moreover, all 
Pouched Animals develop special nipples on the milk-glands, 
which are sucked by the young after birth. These nipples 
project into the cavity of a pouch, or marsupium, in the 
ventral side of the mother. This pouch is supported by 
a couple of marsupial bones. In it the young, which are 



152 



THE EVOLUTION OF MAN 



bom in a very imperfect condition, are carried by the 
mother foj a long time ; until, in fact, they are completely 
develoj^'^d (Fig. 197). In the large Giant Kangaroo, which 




Fig. 197. — The Crab-eating l^ouched Kat {Philander cancrivorus), A 
female with two yoang in its pouch. (After Brehm. ) 



THE POUCHED ANIMALS AS ANCESTORS OF MAN. 153 

attains the height of a man, the embryo develops in the 
uterus but for a month ; it is then born in a very incomplete 
condition, and attains all its fui^ther development in the 
mother's pouch, where, for about nine months, it remains 
attached to the milk-glands. 

All these and other characters 'especially the peculiar 
structure of the internal and external sexual organs of the 
male and female) clearly show that the whole sub-class of 
the Pouched Animals (Marsupialia) are a single group, 
which originated from the promammalian branch. From a 
branch of these Pouched Animals (perh§>ps from several 
blanches) the parent-forms of the higher Mammals, the 
Placental Animals, afterwards sprang. Hence we must 
reckon a whole series of Pouched Animals among the an- 
cestors of the human race ; and these constitute the seven- 
teenth stage in the human pedigree.^^^ 

The remaining stages of our ancestral line, from the 
eighteenth to the twenty-second, all belong to the group oi 
Placental Animals (Placentalia). This very highly de- 
veloped group of Mammals, the third and last, came into 
the world at a considerably later period. No single known 
fossil, belonging to any portion of the Secondaiy or Meso- 
lithic Epoch, can be referred with certainty to a Placental 
Animal, while we have plenty of placental fossils dating 
from ever} part of the Tertiary or Ca^nolithic Epoch. From 
this pal^eontological fact we may provisionally infer that the 
third and last main division of Mammals did not develop 
from the Pouched Animals until the beginning of the 
Csenolithic Epoch, or, at the earliest, till the close of the 
Mesolithic Epoch (during the Chalk Period). In our survey 
of geological formations and periods (pp. 12, 19) we found 



154 THE EVOLUTION OF MAN. 

how comparatively short this whole Tertiary or Caenolithic 
Epoch was. Judging from the relative thicknesses of the 
various strata-formations we were able to sav that this 

ft/ 

whole period, during which Placental Animals first appeared, 
and assumed their respective forms, amounted at most to 
about three per cent, of the entire duration of the organic 
history of the earth. (C£ p. 18.) 

All Placental Animals are distinguished from the two 
lower Mammalian groups already considered, from the 
Cloacal Animals and Pouched Animals, by many prominent 
peculiarities. All these characters are present in Man ; a 
most significant fact. For on the most accurate comparative 
anatomical and ontogenetical researches, we may base the 
irrefutable proposition that Man is in every respect a true 
Placental Animal; in l^imare present all those peculiarities 
in the structure and in the development of the body which 
distinguish Placental Animals from the lower Mammalian 
groups, and at the same time from all other animals. 
Among these characteristic peculiarities the higher develop- 
ment of the brain, the organ of the mind, is especially 
prominent. The fore-brain, or large brain {cerebrum) is 
much more highly developed in these than in lower 
animals. The body (corpus callosum), which, like a bridge, 
connects the two hemispheres of the fore-brain, attains its 
full development only in Placental Animals ; in the Pouched 
Animals and Cloacal Animals it exists merely as an insigni- 
icant rudiment. It is true that in their brain structure 
the lowest of the Placental Animals yet resemble Pouched 
Animals very nearly; but within the Placental gi'oup we 
can trace a continuous series of progressive stages in the 
development of the brain, ascending quite gradually from 



PLACENTAL ANIMALS. 153 

the lowest stage to the very highly developed mind-orgarj 
of the Aloiikey and of Man. (C£ Chapter XX.) Th. 
human mind is but a more highly developed ape-mind. 

The milk-glands of Placental Animals, as of Marsu 
pials, are provided with developed nipples; but the pouch 
in which the immature young of the latter are carried 
about and suckled is never present in the former. Nor are 
the marsupial bones {ossa Tnarsupialia) present in Pla- 
cental Animals ; these bones, which are embedded in the 
abdominal wall, and rest on the anterior edge of the pelvis, 
are common to Pouched Animals and Cloacal Animals, ori- 
ginating from a partial ossification of the tendons of the 
inner oblique muscle of the abdomen. It is only in a few 
beasts of prey that insignificant rudiments of these bones are 
found. The hook-shaped process of the lower jaw, which 
characterizes Pouched Animals, is also entirely wanting irj 
Placental Animals. 

The character, however, which especially distinguishes 
Placental Animals, and which has justly given its name to 
the entire sub-class, is the development of the placenta, or 
vascular cake. We have already spoken of this organ, in 
describing the development of the allantois in the human 
embryo (vol i. p. 882). The urinary sac or allantois, that 
peculiar bladder which grows out of the posterior portion of 
the intestinal canal, is, we found, formed at an early stage in 
the Imm^n embryo just as in the germs of all other Amnion 
Animals. (Cf Figs. 132-135, vol. i. p. 877-880.) The thin wall 
of this sac consists of the same two layers, or skins, as the 
wall of the intestine itself ; internally of the intestinal-glan- 
dular layer, and externally of the intestinal-fibrous layer. 
The cavity of the allantois is filled with fluid ; this primi- 



156 THE EVOLUTION OF MAN. 

tive Tirine must be chiefly the product of the primitive 
kidneys. The intestinal fibrous layer of the allantois is 
traversed by large blood-vessels which accomplish the nutri- 
ment and, especially, the respiration of the embryo ; these 
are the navel-vessels, or umbilical vessels (vol. i. p. 400). In 
all Reptiles and Birds the allantois becomes an immense 
sac, which encloses the embryo with the amnion, and which 
does not coalesce with the outer covering of the egg 
(chorion). In Cloacal Animals (Alonotremata) and Pouched 
Animals {Marsupi(dia) the allantois is also of this natuie. 
It is only in Placental Animals that the allantois develops 
into that very peculiar and remarkable formation, called 
the placenta, or " vascular cake." The nature of the placenta 
is this : the branches of the blood-vessels which traverse the 
wall of the allantois, penetrate into the hollow tufts of the 
chorion, which are inserted into coiTesponding depressions 
in the mucous membrane of the maternal uterus. As this 
mucous membrane is also abundantly supplied with blood- 
vessels, which conduct the mother's blood into the uterus, 
and as the partition between these maternal blood-vessels 
and the embryonic vessels in the chorion-tufts soon becomes 
extremely thin, a direct exchange of substance is soon de- 
veloped between the two sets of blood-vessels, which is ol 
the utmost importance for the nutrition of the young 
Mammal. The maternal blood-vessels do not, however, 
pass directly (anastomosis) into the blood-vessels of the 
embryonic chorion-tufts, so that the two kinds of blood 
simply mix, but the partition between the two sets of 
vessels becomes so thin, that it permits the passage of the 
most important food-materials, freed from unnecessary 
matter (transudation, or diosmosis). The larger the embryo 



THE PLACENTA. 1 5/ 

grows in Placental Animals, and the longer it remains in 
the maternal uterus, the more necessary does it become that 
special structural arrangements should meet the increased 
consumption of food. In this point there is a very striking 
difference between the lower and the higher Mammals. In 
Cloacal Animals and Pouched Animals, in which the embryo 
remains for a comparatively brief time in the uterus, and is 
bom in a very immature condition, the circulation as it exists 
in the yelk-sac and in the allantois suffices for nutrition, as 
in birds and reptiles. In Placental Animals, on the contrary, 
in which gestation is very protracted, and the embryo 
remains much longer in the uterus, there attaining its full 
development within its investing membranes, a new ap- 
paratus is required to convey a direct supply of richer 
nutritive matter ; and this is admirably effected by the 
development of the placenta. 

In order rightly to understand and appreciate the for- 
mation of this placenta and its important modifications in 
different Placental Animals, we must once more glance at the 
external coverings of the mammalian egg. The outermost oi 
these was originally, and during the cleavage of the egg 
and the first formation of the axial portion of the germ, 
formed by the so-called zona j)(^^lucida, and by the thick 
albuminous covering deposited externally on the latter 
(Fig. 19, Fig. 21, z, h, vol. i. p. 178). 

We called these two outer coverings, which afterwards 
amalgamate, the j^'^^ochorion. This prochorioii very soon 
disappears (in man perhaps in the second week of develop- 
ment), and is replaced by the permanent outer egg-mem- 
brane, the chorion. The latter, however, is simply the 
serous membrane, which, as we have already seen, is the 



158 



THE EVOLUTION OF MAN. 



product of the outer germ-layer of the germ-membrane 
vesicle. (See vol. i. p. 401, and Fig. 139, 4, .-;, sh, p. 385.) This 
is at first a very smooth, thin membrane, surrounding the 
entire egg, as a closed spherical vesicle, and consisting of c. 
single layer of exoderm cells. The chorion, however, be- 
comes very soon studded with a number of little protuber- 
ances or tufts (Fig. 139, 5, chi^). These fit themselves into 
indentations in the mucous membrane of the uterus, and 
thus secure the egg to the wall of the latter. The tufts 
are, howevei, not solid, but hollow, like the fino-ers of a 
glove. * Like the whole chorion, these hollow tufts consist of 
a thin layer of cells belonging to the horn-plate. They 
very soon attain an extraordinary development, growino- 
and branching rapidly. In the spaces between them, new 

Fig. 198. — Egg-coverings of 
the human embryo (cliagrain- 
matic) : m, the thick fleshy wall 
of the uterus ; plu, placenta, 
the inner stratum {j^lu) of 
which has extended processes 
between the chorion-tufts {cJiz) 
(chf, tufted, chl, smooth cho- 
rion) ; a, amnion ; ah, amnion 
cavity ; as, amnion sheath of 
the navel-cord (passing down 
into the navel of the embryo, 
which is not represented here) ; 
dg, yelk-duct ; ds, yelk-sac ; 
dv, dr, decidua (dv, true, dr, 
false). The uterus-cavity (uh) 
opens below into the vagina, 
above, on the right hand side, 
into an oviduct (t). (.'Jter 
Kolliker.) 

tufts arise in all directions from the serous membrane, and 
thus before long (in the human embryo in the third week) 




DEVELOPMENT OF THE PLACENTA, 1 59 

the whole outer surface of the egg is covered with a dense 
forest of tufts (Fig. 134). 

These hollow tufts are now penetrated from within by 
the branching blood-vessels, which originate from the in 
testinal fibrous layer of the allantois, and which contain 
the blood of the embryo, introduced through the navel vessels 
(Fig. 198, chz). On the other hand, dense networks of 
blood-vessels develop in the mucous membrane, which 
lines the inner surface of the uterus, particularly in the 
neighbourhood of the depressions into which the chorion- 
tufts penetrate (plu). Th6se vascular networks receive the 
blood of the mother introduced through the uterus vessels. 
The whole mass of these two sets of vessels, which are here 
most intimately connected, together with the connecting 
and enveloping tissues, is called the placenta, or " vascular 
cake." Properly speaking, the placenta consists of two 
quite different, though closely connected, parts ; internally, 
of the embryonic placenta {jjlacenta foetalis, Fig. 198, chz), 
and externally of the maternal placenta {placenta uterina, 
Fig. 198, plu). The latter is formed by the uterine mucous 
membrane and its blood vessels : the former by the 
secondary chorion and the navel vessels of the embryo. 

The mode in which these two "vascular cakes" com- 
bine to form the placenta, as well as the structure, form, 
and size of the latter, differs much in different Placental 
Ajiimals and affords valuable data for natural classification, 
and hence also for the tribal history of the whole sub-class. 
The latter is primarily divisible into two main divisions, 
based on these difterences : the lower Placental Animals, 
which are called Indecidua, and the higher PlacentaJ 

Animals, or Deciduata. 
44 



l6o THE EVOLUTION OF MULN. 

To tlie Iiidecidua, or lower Placental Animals, belong 
two very comprehensive and important vertebrate groups : 
(1) the Hoofed Animals ( Ungulata) — the Tapirs, Ilorses, 
Swine, Ruminants, and others ; (2) the Whale-like animals 
(Cetomorpha) — the Sea-cows, Porpoises, Dolphins, Whales, 
and others. In all these Tndecidua the chorion tufts are 
distributed, singly or in bunches, over the entire surface of 
the chorion, or over the greater part of it. They are but very 
loosely attached to the mucous membrane of the uterus, so 
that the entire outer egg-membrane with its tufts might 
easily and without using force be dt*awn out of the depressions 
in the uterine mucous membrane, just as the hand is with- 
drawn from a glove. The two " vascular cakes " do not 
really coalesce at any point of their contact. Hence, at 
birth the "embryonic cake" (placenta foetalis) is alone 
removed ; the " maternal cake " (placenta uterina) is not 
displaced. The entire mucous membrane of the gravid 
uterus is but little altered, and, at parturition, suffers no 
direct loss of substance. 

The structure of the placenta in the second and higher 
division of Placental Animals, the Deciduata, is very dif 
ferent. To this comprehensive and very highly developed 
mammalian group belong all Beasts of Pre}^ and all Insect- 
eaters, Gnawers (Rodentia), Elephants, Bats, Semi-apes, and, 
lastly, Apes and Man. In all these Deciduata the whole 
surface of the chorion is also at first thickly covered with 
tufts. These, however, afterwards disappear from part of 
the surface, while they develop all the more vigorously in 
the remainder. The smooth chorion (chorion leave, Fig. 198, 
ohl) thus becomes distinct from the tufted chorion (chorion 
(rondosum. Fig. 198, chf). On the former there are only 



INDECIDUA AND DECIDUA. l6l 

minute and scattered tufts, or none at all ; while the lattei 
is thickly overgrown with highly developed and large tufts, 
[n the Deciduata the tufted chorion alone formg the 
placenta. 

Yet more characteristic of the Deciduata is the very 
peculiar and intimate connection which is developed in 
these between the tufted chorion and the contiguous 
portion of the uterine mucous membrane, and which must 
be regarded as a true coalescence. The vascular tufts of 
the chorion push their branches into the sanguineous tissue 
of this mucous membrane in such a way, and the two sets 
of vessels are in such close contact and are so interlaced, 
that the embryonic placenta is no longer distinguishable 
from the maternal placenta ; the two form one whole — a 
compact and apparently simple placenta. Ow'ng to this 
intimate coalescence, a portion of the uterine mucous mem- 
brane of the mother comes away, at birth, with the firmly 
adherent egg-membrane. The portion of the mother's body 
which is thus removed in parturition is called, on account 
of its separable nature, the deciduous membrane (decidua). 
Ail Placental Animals which possess this deciduous mem- 
brane are classed together as Deciduata. The removal of 
this membrane at parturition, of course, causes a greater or 
less loss of blood by the mother, which does not occur in 
the Indecidua. In the Deciduata, moreover, the lost portion 
of the uterine mucous membrane must be replaced, after 
parturition, by a renewal of the tissue. 

The structure of the placenta and deciduous membrane 
is, however, by no means identical throughout the compre- 
licnsive group of Deciduata. On the contrary, there are 
many important difierences in this respect, which are in 



1 62 THE EVOLUTION OF MAN. 

gome degree connected with other important structural 
characters {e.g., the structure of the brain, of the teeth, ot the 
feet), and which may justly, therefore, be turned to account 
in the phylogenetic classification of Placentals. In the first 
place, two great groups of Deciduata may be distinguished 
according to the form of the placenta : in the one group it 
is ring-shaped or girdle-shaped; in the other it is discoid or 
cake-shaped. In Deciduata with girdle-shaped placenta 
(Zonoplacentalia) the poles of the oval egg take no part 
in the formation of the placenta. The " vascular cake " 
resembles a broad ring-like girdle, embracing the central 
zone of the egg. It is so in Beasts of Prey (Carnassia), 
both in the terrestrial forms (Carnivora) and in the marine 
forms (Pinnipedia). A similar girdle-shaped placenta is 
found in the False-hoofed Animals (Chelophora) : the 
elephants, and Klip Das (Hyrax) with its allies, which were 
formerly classed as Hoofed Animals. All these Zonoplacen- 
talia belong to one or more side-branches of the Deciduata, 
which are not nearly allied to Man. 

The second and most highly developed group is formed 
by the Deciduata with discoidal placenta {Discoplacentalia). 
The formation of the placenta is here most localized and 
its structure most fully developed. The placenta forms a 
thick, spongy cake, usually in the form of a circular or 
oval disc, and attached only to one side of the uterine 
waU. The greater part of the embryonic egg-membrane is, 
therefore, smooth, without developed tufts. To the Disco- 
placentalia belong the Semi-apes and Insect-eaters, the 
Diggers (Effbdienta) and the Sloths, Rodents and Bats, 
Apes and Man. Comparative Anatomy enables us to infer 
that of these various orders the Semi-apes are the parent- 



SEMI-APES. 163 

-Toup from which all other Discoplacentals, and perhaps 
even all Deciduous Animals, have developed as divergent 
branches. (Cf. Tables XXIII. and XXIV.) 

The Semi-apes (Prosimice) are now represented only by 
very few forms. These, however, are very interesting, and 
must be regarded as the last remnants of a group once rich 
in forms. This group is certainly very ancient, and was 
probably very prominent during the Eocene Epoch. Their 
present degraded descendants are scattered widely over the 
southern portion of the Old World. Most of the species 
inhabit Madagascar ; a few the Sunda Islands ; a few others 
the continents of Asia and Africa. No living or fossil Semi- 
apes have, as yet, been found in Europe, America, or Aus- 
tralia.-^^^ The widely scattered posterity of the Semi-apes 
is considerably diversified. Some forms seem nearly allied 
to the Marsupials, especially to the Pouched-rats. Others 
(MacTotarsi) are very near akin to the Insect-eaters, and 
yet others (Cheiromys) to the Gnawers (Rodentia). One 
genus (Galeopithecus) forms a direct transition to the Bats. 
Finally, some of the Semi-apes (Brachytarsi) approach very 
near to true Apes. Among the latter are some tail-less forms 
{e.g., the Lori, Stenops, Fig. 199), From these highly in- 
teresting and important relations of the Semi-apes to tht 
various Discoplacental orders, we may fairly infer thai 
of the extant representatives of this group, they are tht 
nearest to the common primitive parent-form. Among the 
direct common ancestors of Apes and Men, there must have 
been some Deciduata which we should class among the 
Semi-apes, were we to see them alive. We may therefore 
consider this order as a special stage, following the Pouched 
Animals, as the eighteenth stage in the human pedigree. 



164 



THE EVOLUTION OF MAN. 



Probably our ancestors among the Semi-apes closely re- 
sembled the extant Brachytarsi or Lemurs {Lertiur, LichaTir- 






J'- " 




Fig. 199. — The Slender Lori of Ceylon (Stenops gracilis). 

otus, Stenops), and, like these, led a quiet life, climbing on 
trees. The extant Semi-apes are mostly nocturnal animals 
of, gentle and melancholy disposition, subsisting on fruits. 



APES. 165 

The Semi-apes are immediately followed by the true 
A-pes (Simice), as the nineteenth stage in the human pedi- 
oree. It has long been beyond doubt that of all animals 
the Apes are in all respects the most nearly allied to Man. 
Just as, on the one side, the lowest Apes approach very near 
to the Semi-apes, so, on the other side, do the highest Apes 
most closely resemble Man. By carefully studying the Com- 
parative Anatomy of Apes and i\Ian, it is possible to trace a 
gradual, uninterrupted advance in the Ape-organization up to 
the purely human structure; and on impartially testing this 
" Ape-question," which has lately been agitated with such 
passionate interest, we shall infallibly have to acknowledge 
the important fact, which was first explicitly laid down by 
Huxley, that "whatever system of organs be studied, the 
comparison of their modifications in the ape series leads to 
one and the same result — that the structural differences 
which separate Man from the Gorilla and Chimpanzee are 
not so great as those which separate the Gorilla from the 
lower Apes." In phylogenetic language this pregnant law 
established in so masterly a manner by Huxley, is equiva- 
lent to the popular phrase : Man is descended from the Ape. 
In order to become convinced of the truth of this law, 
let us now once more consider the placenta and deciduous 
membrane, on the varied structure of which we justly laid 
special stress. Men and Apes, in the structure of theii* disc- 
shaped placenta and m their decidua, do, indeed, coincide 
on the whole with all other Discoplaeental Animals. But 
in the more delicate structure of these parts Man is dis- 
tinguished by peculiarities which he shares only with Apes, 
and which are absent in other Deciduata. Thus in Man 
and in the Apes three distinct parts are recognized in the 



1 66 



I'HE EVOLUTION OF MAN 



deciduous membrane ; these parts may be called the outer, 
the inner, and the placental deciduous membrane. The 
outer or true membrane {d. externa or vera, Fig. 198, dv, 
Fig. 200, g)y is that portion of the uterine mucous membrane 
which coats the internal surface of the uterus wherever the 




Fig. 200. — Human embryo, twelve weeks old, with its coverings ; natural 
size. The navel cord passes from the navel to the placenta : 6, amnion ; 
c, chorion; </, placenta; d\ remains of tufts on the smooth chorion;/, de- 
cidtia reflexa (inner) ; </, decidtia vera (outer). (After Bernhard Schultze.) 

latter is not attached to the placenta. The placental or 
spongy deciduous membrane {d. jplacentalis or serotina^ 
Fig. 198j_^Zt^5 Fig. 200, d) is simply the maternal placenta 



THE DECIDUOUS MEMBRANE IN MAN AND APES. 1 6/ 

itself, or the maternal part of the " vascular cake " {pla^ 
centa uterina), i.e., that part of the uterine mucous mem- 
brane which coalesces intimately with the chorion- tufts of 




Fig. 201. — Mature human embryo (at the end of pregnancy), in its natural 
jwsition, taken out of the uterus. On the inner surface of the latter (on 
the left) is the placenta, which is attached to the navel of the child by the 
narel cord. (After Bernhard Schultze.) 

the embryonic placenta {^^lacenta foetalis). Lastly, the 
inner or false deciduous membrane (d. interna or rejiexa. 
Fig. 198, dr, Fig. 200, /) is that portion of the uterine mucous 
membrane which, as a peculiar thin envelope, covers all the 
rest of the egg-surface, lying immediately over the tuftless 
smooth chorion {chorion Iceve). The origin of these three 
distinct deciduous membranes, concerning which erroneous 
notions have been entertained (still retained in the nomen- 
clature), is plain enough ; the external or true deciduous 



1 68 THE EVOLUTION OF MAN. 

membrane is a peculiar modification, afterwards lost, of the 
superficial layer of the original mucous membrane of the 
utoi-us. The placental membrane is that portion of the 
preceding which is completely modified by the intrusion of 
the chorion-tufts and is employed in forming the placenta. 
Lastly, the inner deciduous membrane is formed by a 
ring-shaped fold of the mucous membrane (at the point 
of union of the d. vera and the d. serotina) which rises, 
•grows round the egg, and closes in the same way as the 
amnion.^^^ 

The peculiar anatomical characters which- mark the human 
L'gg-membrane re-occur, in the same form, only in Apes. Al] 
other Discoplacental Animals present greater or less differ- 
ences in these points, the conditions being generally more 
simple. This is the case, for instance, in the structure of 
the placenta itself, in the coalescence of the chorion tufts 
with the deddua serotina. The matured human placenta 
is a circular (rarely oval) disc of a soft, spongy character, 
6 to 8 inches in diameter, about 1 inch thick, and weiohino 
from 1 to l^^ lb. Its convex, external surface (that which 
coalesces with the uterus) is very uneven, and tufted. Its 
internal, concave surface (that which is turned towards the 
cavity of the egg) is quite smooth, and clothed by the amnion 
(Fig. 198, a). From near the centre of the placenta springs 
the navel cord (funiculus v/mhilicalis), the development 
of which we have already observed (vol. L p. 883). It also is 
coated by the amnion as with a sheath, which at the navel 
end passes directly into the abdominal skin (Fig. 200, 201). 
The mature navel cord is a cylindrical cord, coiled spirally 
around its axis, and usually about 20 inches long and 5- inch 
thick. It consists of gelatinous connective tissues (" Whar- 



THE HUMAN PLACENTA. 1 69 

ton's jelly "), in which are contained the remnants of the 
yelk- vessels and of the great navel vessels ; the two navel 
arteries which convey the blood of the embryo to the pla- 
centa, and the great navel vein which brings back the blood 
from the latter to the heart. The numerous fine branches 
of these embr^^onic navel vessels pass into the branched 
chorion tufts of the foetal placenta, and with these, finally, 
grow, in a very peculiar way, into large blood-filled cavities, 
which spread themselves in the uterine placenta and con- 
tain blood from the mother. The anatomical relations, very 
complex and difiicult to comprehend, which are developed 
between the embryonic and the maternal placenta, exist in 
this form only in Man and in the higher Apes, while in aU 
other Deciduous Animals their form is more or less different. 
The navel cord, also, is proportionately longer in Man and 
in Apes than in other Mammals. 

As in these important characters, so also in every other 
morphological respect, Man appears as a member of the 
order of Apes, and cannot be separated from the latter. The 
great originator of systematic description of nature, Karl 
Linnaeus, with prophetic penetration, united Men, Apes, 
Semi-apes, and Bats in a single natural division, under the 
name of Primates, that is, the first, the lords of the animal 
kingdom. Later naturalists dissolved this order of Primates. 
The GSttingen anatoixdst, Blumenbach, first placed Man in 
a special order, which he called that of Two-handed Animals 
{BiinaTia) ; in a second order, he united Apes and Semi- 
apes under the name of Four-handed Animals (Quad- 
ruma,na), while a third order included the distantly related 
Bats (Chiroptera). The separation of the Bimana and 
Quadrumana was retained by Cuvier and most succeeding 



I/O THE EVOLUTION OF MAN. 

/-oologists. It seems very important, but is really wholly 
unjustifiable. This was first shown in the year 1863 by 
Huxley. Supported by very accurate Comparative Anato- 
mical researches, he proved that Apes are as " two-handed " 
as Men, or, conversely, that Men are as " four-handed " as 
Apes. Huxley showed, with convincing clearness, that the 
ideas previously held of the hand and the foot were false, 
and were incorrectly founded on physiological instead of on 
morphological distinctions. The circumstance that in the 
hand, the thumb may be opposed to the other four fingers, 
thus permitting the act of grasping, appeared especially to 
distinguish the hand from the foot, in which the correspond- 
ing great toe cannot be thus opposed to the four remaining 
toes. Apes, on the contrary, can grasp in this way with the 
hind-foot as well as with the fore-foot, and were therefore 
regarded as four-handed. Many tribes, however, among the 
lower races of men, especially many negro tribes, use the foot 
in the same way as the hand. In consequence of early habit 
and continued practice, they are able to grasp as well with 
the foot as with the hand (for example, in climbing, they 
grasp the branches of trees). Even new-bom children of our 
own race have a very strong grasping power in the great toe, 
with which they can hold a spoon as fast as with the hand. 
The physiological distinction between hand and foot can, 
therefore, neither be strictly carried out, nor scientifically 
established. Morphological characters must be used for this 
purpose. 

A sharp morphological distinction of this kind — that is, 
»ne founded on anatomical structure — between hand and 
foot, between the anterior and the posterior limbs, is actually 
possible. There are essential and permanent difierences 



MAN AND APK I/I 

both in the structure of the bony skeleton and in that of 
the muscles which are attached to the hand and the foot ; 
and these are exactly the same in Man and in the Ape. 
There is, for instance, an essential difference in the arrange- 
ment and number of the wrist-bones of the hand {carpus) 
and the ankle-bones of the foot {tarsus). The muscle-masses 
present equally constant differences. The posterior ex- 
tremity, the foot, has always three muscles (a short flexor 
muscle, a short extensor muscle, and a long muscle attached 
to the muscles of the tibia) which are never present in 
the anterior extremity, the hand. The disposition of the 
muscles is also very different in the two sets of limbs. 
These characteristic differences between the anterior and 
the posterior extremities occur in Man just as in Apes. 
There can, therefore, be no doubt, that the foot of the 
Ape deserves the name as truly as that of the Man ; and 
that all true Apes are as genuinely two-handed animals 
{Bimana) as Man. Thus the usual distinction of the Apes 
as Quadrumana is wholly unjustifiable. 

It might now be asked whether, quite apart from these, 
there are not other marks by which Man is more widely 
separated from the Apes than are the difierent species of 
Apes from each other. Huxley has given a final negative 
to this question so convincingly, that the opposition now 
raised against him in many quarters must be regarded as 
completely unfounded and ineffective. Based on an accurate 
study of the Comparative Anatomy of all parts of the body, 
Huxley brought forward very significant proof that, in 
every anatomical respect, the difierences between the highest 
and the lowest Apes are greater than the corresponding 
diflferences between the highest Apes and Man. He ther©- 



1/2 THE EVOLUTION OF MAN. 

fore restored Linnseus's order of Primates (excluding the 
Bats), and divided it into three different sub-orders, the 
first of which is formed by the Semi-apes (Lemurida), the 
second by the true Apes (Simiadce), and the third by Men 
(Anthropidce)}^^ 

Yet, if we proceed logically and without prejudice, in 
accordance with the principles of scientific reasoning, we 
find, on the basis of Huxley's own law, this division in- 
adequate, and must go considerably further. As I first 
showed in 1866, in treating this question in my Generelle 
Morphologie, we are fully justified in taking at least one 
impoii:ant step further, in assigning to Man his natural 
place in one of the divisions of the Ape-order. All the 
characters distinctive of this one division of the Apes are 
present in Man, while they are absent in other Apes. We 
are, therefore, not justified in forming a distinct order for 
Man apart from the true Apes. 

The order of the true Apes (Simice), the Semi-apes being 
excluded, has long been divided into two natural main 
groups, which, among other points, are distinguished by 
their geographical distribution. Those of one division 
(Hesperopitheci, or Western Apes) live in the New World, 
in America. The other division, to which Man belongs, is 
that of the Heopitheci, or Eastern Apes ; these live in the 
Old World, in Asia, Africa, and, formerly, in Europe. All 
the Apes of the Old World, all Heopitheci, share, in common 
with Man, all those characteristics to which special promin- 
ence is justly given, in distinguishing these two groups of 
^pes, in zoological classification ; among these characteristics 
the structure of the teeth is most prominent. The objec- 
tion is at once evident that the teeth are, in a physiological 



THE TEETH. 173 

sense, much too subordinate a part of the body to justify so 
great a weight being attached to their structure in so im- 
portant a question. There are, however, good reasons for 
this prominent consideration of the structure of the teeth ; 
and it is with perfect correctness and propriety that sys- 
tematic zoologists have, for more than a century, given 
special weight to this character in systematically dis- 
tinguishing and arranging the mammaHan orders. The 
number, form, and disposition of the teeth are transmitted 
much more accurately within the respective orders of the 
mammals than are most other zoological characteristics. 
The structure of the human teeth is well known. In matu- 
rity there are 32 teeth in our jaws, and of these 32 teeth, 
8 are front-teeth, 4 cannie-teeth, and 20 molar-teeth. The 
eight front-teeth or incisors {denies incisivi), which are 
situated in the centre of the jaws, exhibit characteristic 
differences in the upper and lower jaw. In the upper the 
inner incisors are larger than the outer; in the lower jaw, 
on the contrary, the inner incisors are smaller than the 
outer. Next to these, on each side, both in the upper and 
lower jaw, is a corner- tooth, which is larger than the in- 
cisors, the so-called eye-tooth, or canine (dens caninus). 
Sometimes this tooth becomes very prominent in Men, as in 
most Apes and many other Mammals, and forms a sort of 
tusk. Finally, next to this, on each side, and in each jaw, 
ire situated five back-teeth, or molar- teeth (denies molar es\ 
of which the two foremost (the bicuspid teeth) are small, 
have but a single fang, and are subject to the change of 
teeth, while the three hinder molars are much larger, have 
two fangs, and do not appear till after the temporary teetn 
have been shed (so-called "grinders"). The Apes of the 



1/4 THE EVOLUTION OF MAN. 

Old World have exactly this human structure of the teeth, — 
all Apes which have as yet been found, either living or as 
fossils, in Africa, Asia, and Europe. All Apes of the New 
World, on the contrary, all American Apes, have an extra 
tooth on both sides of each jaw ; this is a biscupid tooth. 
Thus they have six back-teeth on both sides of each jaw, — 
in all, thirty-six teeth. This characteristic difference be- 
tween the Eastern and Western Apes has been so constantly 
transmitted within the two groups, that it is of the greatest 
value to us. A small family of South American Apes does, 
indeed, appear to form an exception in this respect. The 
pretty little Silk Apes, or Marmosets (Ilapalida), namely, to 
which the Brush-monkey (Midas) and the tufted Marmoset 
(Jacchus) belong, have but five back-teeth in each half of 
the jaw, instead of six, and, accordingly, seem to approach 
nearer the Eastern Apes. But on closer observation it 
is found that, like all the Western Apes, they have the 
three biscupids, and that the hindmost grinder has been 
lost. Thus this apparent exception confirms the value of 
the distinction. 

Among the other marks by which the two main groups 
of the Apes are distinguished, the structure of the nose is 
specially important and prominent. In all Old World Apes 
the structure of the nose is the same as in Man ; namely, a 
comparatively narrow partition of the two halves, so that 
the nostrils are directed downwards. In a few Eastern Apes, 
the nose projects as prominently and is as characteristically 
formed as in Man. We have already called attention, 
in this respect, to the remarkable Nose-ape (Semno- 
pitheciis nasicus), which has a well-curved and long nose 
(Fig. 202). Most (»f the Eastern Apes have, it is true, a 



THE NOSE. 



175 



somewhat flatter nose, as, for instance, has the white-nosed 
Sea-cat (Cercopithecus petaurista, Fig. 203) ; yet in all the 
partition of the nose is narrow and thin. On the contrary, 
all American Apes have a different nasal structure. In 
them, the partition is peculiarly broadened and thickened 
below, and the wings of the nose are not developed, in con- 
sequence of which the nostiils are not below, but are 
turned outwards. This characteristic difference in the 
structure of the nose has also been so accurately trans- 




FiG. 202. — Head of Nose. ape (Semnopithecus nasicus). 

Fig. 203. — The white-nosed Sea-cat (Cercopithecus petauristd). 



mittod in both groups, that, on account of it, the Apes of 
the New World have been called Flat-nosed (Platyrhince\ 
and those of the Old World Narrow-nosed (Gatarhince). 
The former are, on the average, inferior in organization. 



45 



1/6 THE EVOLUTION OP MAK. 

The division of the order of Apes into two sub-orders, 
the PlatyrhincB and the Caiarhince, is, on account of the 
constant hereditary characters, now generally accepted by 
zoologists, and receives much support from the geographical 
distribution of the two groups between the New and Old 
Worlds. From this follows the direct inference, very im- 
portant in its bearing on the Phylogeny of Apes, that, from 
the primaeval common parent-form of the Ape-order, two 
diverging lines branched out at a very early period, one of 
which spread over the New World, the other over the Old. 
It is certain that all the Flat-nosed Apes, on the one hand, 
are descendants of a common parent-form, and, on the other 
hand, all the Narrow-nosed Apes from another 

An inference concerning our own pedigree may be drawn 
from this. Man has exactly the same characters, the same 
peculiar formation o£ the teeth and nose, as all the 
Catarhinae, and is as thoroughly distinguished by these 
charateristics from the Platyrhinae. We are therefore com- 
pelled, in classifying the Primates, to assign to Man a place 
in the Narrow-nosed group. The bearing of this on our 
tribal history is, that Man is immediately related in blood 
to the apes of the Old World, and may be traced from a 
parent-form common to all other Catarhinae also. Man is 
a genuine Narrow-nosed Ape in his whole structure and 
in origin, and has descended from some unknown, extinct 
Catarhine form in the Old World. On the other hand, the 
Apes of the New World, the Flat-nosed group, constitute a 
diverging branch of our family tree, and stand in no near 
genealogical relation to the human race. 

We have now reduced the circle of our nearest aUies 
to the small group, containing comparatively few forraii^ 



MAN'S RELATION TO APES. 1/7 

which is represented by the sub-order of the Narrow-nosed^ 
or Eastern Apes. Finally, the question which now re- 
mains to be answered is — what position in this sub-order 
must be assigned to Man, and whether other inferences as 
to the structure of our immediate ancestors may be drawn 
from this position. The comprehensive and acute researches 
into the Comparative Anatomy of Man and the various 
Catarhinae, which Huxley has recorded in his work on the 
" Evidence as to Man's Place in Nature," are of the greatest 
value in furnishing the answer to these important questions. 
The inevitable conclusion is, that the diiFerence between 
Man and the highest Narrow-nosed Apes (the Gorilla, Chim- 
panzee, Orang) is slighter in every respect than the corre- 
sponding differences between the highest and the lowest 
Catarhines (the Sea-cat, Macaque, Baboon). Even within 
the small group of the Tail-less man-like Apes {Anihro- 
poides) the several genera do not differ less from each other 
than they do from Men. This is seen by a glance at the 
skeletons represented here, as arranged by Huxley (Figs. 
204j-208). If the skull, or the vertebral column, together 
with the rib-system, or the anterior or posterior members, 
are compared; or if the comparison is extended to the 
muscular system, the circulatory system, the brain, etc., 
a candid and unprejudiced examination always results in 
the same conclusion, that Man does not differ more from 
the higher Catarhines than the extreme forms of the latter 
(for example, the Gorilla and Baboon) differ from each 
other. "We can, therefore, complete the important propo- 
sition already quoted^ from Huxley : We may take what- 
ever system of organs we will, — ^the comparison of their 
modifications within the ranks of the Catarhinse leads us 



178 



THE EVOLUTION OF MAN; 






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■VOLUTION OF MAN FROM APES. 1/9 

to one and the same conclusion : that the anatomical dif- 
ferences that distinguish Man from the most highly developed 
Catarhinse (the Orang, Gorilla, Chimpanzee), are not so great 
as those which separate the latter from the lowest Catarhinae 
(Sea-cat, Macaque, Baboon). 

We must, therefore, consider the proof complete, that Man 
is descended from other Narrow-nosed Apes (Catarhi/noB), 
Although future researches into the Comparative Anatomy 
and Ontogeny of the existing Catarhines, as well as of their 
fossil relatives, promise us various new details, yet no 
future discovery can ever overthrow that important pro- 
position. Our Catarhine ancestors must, of course, have 
passed through a long series of varied forms, before Man 
finally developed as the most perfect form. The following 
must be considered as the most important advances by 
which this " Creation of Man," his differentiation from the 
most nearly allied Catarhine Apes, was efiected : Habituation 
fco upright carriage and, in connection with this, the greater 
differentiation of the anterior and posterior limbs ; also, the 
development of articulate speech and its organ, the larynx ; 
and lastly, and especially, the more perfect development of 
the brain and its function, the soul ; sexual selection must 
have exerted an extraordinarily important influence, as 
Darwin has conclusively proved in his celebrated work on 
sexual selection.^® 

With reference to these advances, we may, among our 
Catarhine ancestors, distinguish at least four important 
ancestral stages, marking prominent epochs in the great 
historical process of the origin of Man. As the nineteenth 
stage in the human pedigree, next to the Semi-apes, we may 
place the oldest and lowest Catarhine Apes, which developed 



l80 THE EVOLUTION OF MAN. 

from the former by the formation of the chaiacteristic 
catarhine head, and by the peculiar modification of the 
teeth, the nose, and the brain. This oldest parent-form of 
the whole Catarhine group must, certainly, have been 
thickly covered with hair, and must have had a long tail ; 
was, in fact, a Tailed Ape (Menocerca, Fig. 203). They 
were already in existence during the earlier part of the 
Tertiary Epoch (during the Eocene Period), as is shown by 
fossil remains of Eocene Catarhines. Among extant Tailed 
Apes, the Slender Apes (Semnopitheci) are perhaps most 
nearly related to this parent-form.^^ 

As the twentieth stage in the human pedigree, next to 
these Tailed Apes, we must rank the Tail-less man-like Apes 
(Anthropoides), under which name the most highly de- 
veloped Catarhines, those most nearly related to Man, have 
been grouped. They originated from the Tailed Catarhines, 
by the loss of the tail, the partial loss of their hairy cover- 
ing, and the further development of the brain, the latter 
being indicated in the preponderating development of the 
brain-skull over the facial skull. At the present time but 
few forms of this remarkable family are in existence ; they 
are distributed into two different groups, an African and an 
Asiatic group. The African Man-like Apes are limited to 
the western part of tropical Africs., but are probably dis- 
tributed over Central Africa in several species. Only two 
species are well known : the Goiilla {Pongo gorilla, or 
Gorilla engina), the largest of all Apes (Fig. 207) ; and the 
smaller Chimpanzee (Fongo troglodytes, or Engeco troglo- 
dytes), which may be seen in several zoological gardens 
(Figs. 206, Plate XIV. Figs. 1, 2). Both the African Man- 
like Apes are black in colour, and like their countrymen, 



HAECKELS EVOLUTION OF MA>f. 



PLATE XIV, 




1 Gorilla. 






Pirn- ^Ai \y~^Z'^At^ 

'll^7i>h-r il.-t . 
















3. Orang. 



4. Negro. 



ICAN-LIEE APEa l8l 

the Negroes, have the head long from back to front (doli- 
chocephalic). The Asiatic Man-like Apes are, on the con- 
trary mostly of a brown, or yellowish brown colour, and 
have the head short from back to front (brachycephalic), 
like their countrymen, the Malays and Mongols. The 
largest Asiatic Man-like Ape is the well-known Orang, or 
Orang-outang (Fig. 128), which is indigenous in the Sunda 
Islands (Borneo, Sumatra), and is brown in colour. Two 
species have recently been distinguished : the great Orang 
(Satyrus Orang ; Fig. 205, Plate XIV. Fig. 3), and the small 
Orang (Satyrus morio). A genus of smaller Anthropoids 
(Fig. 204), the Gibbons (Hylobatea), live on the main-land 
of Southern Asia and on the Sunda Islands ; from four to 
eight different species of these have been distinguished. 
Neither of these living Anthropoids can be indicated as the 
Ape absolutely most like Man. The Gorilla approaches 
nearest to Man in the structure of the hand and foot, the 
Chimpanzee in important structural details in the skull, 
the Orang in the development of the brain, and the Gibbon 
in that of the thorax. It is evident that no single one of 
these existing Man-like Apes is among the direct ancestors 
of the human race ; they are all the last scattered remnants 
of an old, catarhine branch, once numerous, from which the 
human race has developed as a special branch and in a 
special direction. 

Although Man (Homo) ranks immediately next to this 
anthropoid family, from which he doubtless directly origin- 
ated, yet the Ape-men (Pithecanthropi) may be inserted 
here, as an important intermediate form between the two, 
and as the twenty-first stage in our ancestral series. In the 
"Natural History of Creation*' (voL ii p. 293), I have 



1 82 THE EVOLUTION OF MAW. 

applied this name to the speechless Primitive Men (Alali\ 
who made their appearance in what is usually called the 
human form, that is, having the general structure of Men 
(especially in the differentiation of the limbs) — but yet 
being destitute of one of the most important qualities of 
Man, namely, articulate speech, as well as of the higher 
mental development connected with speech. The higher 
differentiation of the larynx and of the brain occasioned by 
the latter, first gave rise to the true " Man." 

Comparative Philology has recently shown that the 
present, human language is polyphyletic in origin, that 
several, and probably many, different original languages 
must be recognized, as having developed independently from 
each other. The history of the development of languages 
also teaches us (its Ontogeny in every child, as well as its 
Phylogeny in every race), that the actual rational lan- 
guage of men developed gradually, only after the body 
had developed into the specific human form. It is even 
probable that the formation of language did not begin till 
after the differentiation of the various species, or races of 
men, and this presumably occurred in the beginning of the 
Quaternary Epoch, or the Diluvial Period. The Ape-men, 
or Alaliy were therefore probably already in existence 
toward the close of the Tertiary Epoch, during the Pliocene 
Period, perhaps even as early as the Miocene Period.^^ 

Lastly, the genuine or speaking human being (Homo) 
must be considered as the twenty-second and final stage 
in our animal pedigree. Man originated from the pre- 
ceding stage in consequence of the gradual improvement 
of inarticulate animal sounds into true human articulate 
speech. Only very uncertain conjectures can be formed at 



PRIMEVAL MAN. 1 83 

to the time and place of this true "Creation of Man.** 
It is probable that Primgeval Man originated during the 
Diluvial Epoch, in the torrid zone of the Old World, either 
on the continent of tropical Asia or Africa, or on an earlier 
continent which has now sunk below the surface of the Indian 
Ocean, and which extended from Eastern Africa (Madagas- 
car and Abyssinia) to Eastern Asia (the Sunda Islands 
and Eastern India). In my " Natural History of Creation " 
(Chapter XXIII. and Table XV), I have already fuUy 
discussed the important evidence as to the former existence 
of this large continent, called Lemuria, and how the distribu- 
tion of the various species and races of men probably took 
place from this " Paradise " over the surface of the earth 
In the same place, I have also fully discussed the inter- 
relations of the various races and species of the human 
race.^^ 



TABLE XXII. 

Systematic Survey of the Periods in the Tribal History of the 

Human Race. 
(Compare Table VIII., vol. i. p. 402.) 



FIRST MAIN PERIOD IN TRIBAL HISTORY. 

The Flastid Anoeston of Man. 

The form of the ancestors of man is equal to the simple indiyidiuJ of ikt 
flirit order, • single plastid. 

First Stage : Moneron Series (Fig. 163, p. 46). 
The ancestors of man are single, living, simple cytods. 

Second Stage : Amoeba Series (Fig. 167 p. 68). 
The ancestoi's of man are single, living, nniple cells. 

SECOND MAIN PERIOD IN TRIBAL HISTORY. 

The many-celled Primitive Animal Ancestors of Man. 

The ancestors of man consist of a closely -united society of many homo- 
geneous cells ; hence their form-value is that of individuals of the second 
order, of Idorgana. 

Third Stage : Synamoeha Series (Fig. 170, p. 56). 

The ancestors of man are many-celled primitive animals of the simplest 
kind : solid masses of simple, homogeneous cells. 

Fourth Stage : Flanssa Series (Figs. 172, 173, p. 60). 

The ancest« )rs of man are many-celled primitive animals of a charactei 
like that of the Magosphcera and certain planula-larvsa, of equal rank with 
the ontogenetic Blastula or BlastosphoBra ; hollow spheres, the wall of which 
cunsists of a singlt stratom of ciliated cells. 



SYSTEMATIC SURVEY OF THE HUilAN RACl, I83 

THIRD MAIN PERIOD IN TRIBAL HISTORY, 

The Inyertebrate Intestinal Animftl Ancestors of Uao. 

The iJicestors of man have the form-ralne of individnals of the third 
order, of inartiOTilate individuals. The body encloses an intestinal cavity 
with a month, and consists at first of two primary germ-lftjers, afterwards 
of four secondary germ-layera. 

Fifth Stage : Gartrsea Series (Figs. 174-179, p. 66). 

The ancestors of man have the form-value and stmoture of a Gastmla. 
The body consists merely of a simple primitive intestine, the wall of which 
is formed of the two primary germ-layers. 

Sixth Stage : Chordonium Series (Figs. 184-188, p. 80-90), 

The ancestors of man are worms : at first, primitive worms, allied to the 
Turhellaria; afterwards worms of higher rank, Scoimda; finally, notochord* 
animals with the organization of the ascidian larvae. The body is composed 
of four secondary germ-layers. 

FOURTH MAIN PERIOD IN TRIBAL HISTORY. 

The Vertebrate Ancestors of Man. 

The ancestors of man are vertebrates, and their form-value is, therefore, - 
that of an articulated individual, or a chain of metamera. The skin-sensory 
layer is specialized into the horn-plate, medullary tube, and primitive 
kidneys. The skin-fibrous layer has divided into the leather.plate, primitive 
vertebrae (muscular plate and skeleton-plate), and the notochord. From 
the intestinal.fibrous layer originates the heart with the main blood-vessels 
and the fleshy intestinal wall. From the intestinal-glandular layer, the 
epithelium of the intestinal tube is formed. The formation of metamera is 
constant. 

Seventh Stage : Aorania Series (Fig. 189 ; PL XL Fig. 15). 

The ancestors of man are skull-less vertebrates, like the extant Amphi- 
oxos. The body already forms a chain of metamera, several primitive 
vertebrae having separated off. The head is not yet entirely distinct from 
the trurk. The medullary tube has not separated into brain-bladders. The 
heart is very simple, without chambers. The skull is still wanting ; as are 
also the jaws and limbs. 



1 86 THE EVOLUTION OF MAN. 

Eighth Stage: Monorhina Series (Fig. 190; PI. XI. Fig. 1(J). 

The ancestors of man are jaw-less skulled animals (resembling the 
developed Myxinoides and Petromyzontes) . The number of the metamera is 
increasing. The head is becoming more distinctly differentiated from the 
Srnnk. The anterior end of the medullary tube swells into a bladder-like 
itructure and forms the brain, which is soon differentiated into five brain- 
bladders. At the sides of these appear the three higher organs of sense. 
The heart is divided into auricle and ventricle. The jaws, limbs, and 
iwimming-bladder are still wanting. 

Ninth Stage : lohthyoda Series (Figs. 191, 192; PI. XII. and XIH.). 

The ancestors of man are fish-like skulled animals : first, Primitive 
Fishes {Selachii), then mnd-fishes (Bipneusta), then gilled Batrachians (Sozura). 
The ancestors belonging to this Ichthyoda stage develop two pairs of limbs: 
a pair of anterior limbs (pectoral fins) and a pair of posterior limbs (ventral 
fins). The gill-arches are formed between the gill-openings, and from them 
are formed the first pair of jaw-arches (upper and lower jaws). The 
swimming-bladder (lungs), liver, and pancreas grow from the intestinal 
canal. 

Tenth Stage : Anmiota Series (Figs. 195-208 ; PL XTV.). 

The ancestors of man are amnion-animals or gill-less vertebrates : first, 
Primitive amniota (Protamnia), then Primitive mammals (Monotrema) ; next, 
Pouched animals (Marsupialta) j then Semi-apes (Prosimiae), and, lastly. 
Apes {Sitnioe), The ape-ancestors of man are first tailed Catarhini, theo 
tail-less Catarhini (Anthropoides), then speechless Ape-men (Alali), and at 
last genuine, speaking men. The ancestors belonging to this amnionata 
series develop an amnion and allantois, and graduallj acquire the mam. 
malian stroctare, and at lost the specific homaa form. 



( 187 ) 



TABLE XXIII. 

SjBtematio Survey of the Phylogenetic Classification of MammAls. 



L 

Virst 
Sab-class of 


/ Cloacal 
Animals 
{Monotrema, or 
Ornithodelphia) 


1. Primitive Mammata 

2. Beaked Animals 


Promammalia 
OmithosUma 


IL 

Second 
Sub-class of 


' Pouched 
Animals 

{^Marsupialia, or 
Diddphia) 


3. Herbivorous Pouched Animals 

4. Carnivorous i'ouched Animals 


Botanophaga 
Zoophaga 




in. (a) 

, Placental 
Mammals with- 


' 6. Hoofed Animals r Single-hoofed 
Ungulata \ Double-hoofed 


Perissodactyla 

Artiodactyla 




out Decidua, with 
Tufted Placenta 

Indecidua 
yilliplacentalia 


6. Whale-like 
Animals 
Cetomorpha 


 

Sea-cows 
Whales 


Sirenia 
Cetaoea 


/ 


III. (6) 

Placental 
Mammals with 


7. Pseudo-hoofed 

Animals 

Chdophora 


Rock Conies 
Elephants 


lAimnungia 
Prohoscidta 


m. 

Third 
Snb-class of 


Decidua, with ^ 
Girdle Placenta 
Becidimta 
Zonoplacen talia 


8. Beasts of Prey 
Carmuaia 
\ 


' Land Beasts of 
J prey 

^ Marine Beasts of 
( prey 


Camivora 
Piimipedia 


Placental 
Mammals 
{Placentalia, 




9. Semi-apes 
Prosimict 


' Fingered animals 
J Long-footed 
"i Flying Lemur 
( Lemurs 


Leptodactyla 
Macrotarsi 
Ptenopleura 
Brachytarti 


or Mono- 
delphia) 


ni. (e) 

Placental 
Manoials with / 
Decidua, with ( 
Discoid Placenta 


10. Gnawing Anl 

mals 
Rodentia 

11. Toothless 
Edentata 


_ / Squirrel species 
" 1 Mouse species 

J Porcupine species 

' Hare species 

( Digging an'wiftls 
I Sloths 


Seiuromorpha 
Myomorpha 
Hystrichomorpha 
Lagomorpha 

Effodientia 
Bradypoda 




Deciduata 
DiKoplacentalia 


12. Insect-eaters 
Insectiwra 


I With CoBP.um 
1 Without Coecnm 


Mmotyphta 
Lipotyphla 




\ 


13. Flying Animals ) Flying Foxes 
Chiroptera ( Bats 


Pterocynes 
Nycteridu 






14. Apes 
[ SitMm 


( Flat-nosed 
\liarTOw-D08ed Apes 


Platyrhina 
Catarhtna 



C i88 ) 



TABLE XXIV. 

Pedigree of MammaU, 



Elephants 
Prohoscidta 

Rook Conies 

TjOk'n'mingia 



False-hoofed 

Chelophora Flat-nosed Apes 
PlatyrhincB 



IHan 
Homiues 

I Bats 

Man-like Apes Ny derides 
Anthropoidea \ 

I Flying Foxes 

Narrow-nosed Apes Pterocynes 
CatarhincB jFIstng Animals 
Chiroptera 



Sea beasts of ptvy 
Pirmipedia 



®ttafoino[*^nitnaIs 

Eodentia Spcs 

Fingered animals Simiae 

Whales Leptodactyla 

Cetacea | 

I ^" « -"' 

Sea-Cows I 

Sirenia \ 

B2Ef)aIc=fnmil2 

Cetomorpha 



Land beasts of prey 
Carnwora 
Flying Lemurs | 

Ptenopleura Bcasts of ^ttg 
I Camassia 



Lemnrs 

Brachyta/rsi 



Toothless 
Edentata 



Insect-eaters 

Long-footed Insectivora 

Macrotarn 



^aoifa Animal! 
TTngulata 



SBaitfjDut BectHtui 
Indeciduata 



Semi -apes 
ProsimicB 

©tciliuous Animals 
Deoiduata 



^lacnttal Inimals 
Placentalia 



Herbivorous Pouched Animals 
Marsvpialia hota/nophaga 



Carnivorous Pouched Animals 
Marsupialia zoophaga 

I 



Beaked Animals 

Omithostoma 

! 



^oucf}eti "Unttnalf 
Marsupialia 



Primitive Mammals 

Promammalia 

Cloaca I Animals 






hasckel's evolution of man. 



PLATE XV, 



PEDIGREE OF MAN. 




( i89 ) 

TABLE XXV. 

Pedigree of Apes. 



Homo 



AlaluB 



Gorilla 

Ohimpansee Oorilla 

Engeco 



African 



Or&ng-Ontsng 
Satyrut 



Gibbon 

Hylohatm 



•Hsiattc 



fHan4t^e "apes 
Anthropoides 



Silk Apes 
Hapalida 



Clntcli. tails 
Lahidocerca 



Nose Apes 
Tall Apes NaaaM* 

Sermuypithecus 



Sea Cat 

Cercopithecus 



Baboons 
Cynoeephahts 

I 



Flap.tails 
Aphyocerea 



aipes of j^dD WLoxln 

Flat-nosed 
PlatyrliinaB 



Catlcti "apes 
Menoceroa 



Slpes of ^Vn WioxtU 

Narrow-nosed 
Catarhina 



Riniifla 



Pzonmui 



CHAPTER XX. 

THE HISTORY OF THE EVOLUTION OF THE EPIDERMIS 
AND THE NERVOUS SYSTEM. 

A.uiraal and Vegetative Organ. systema. — Original Eelations of these to the 
Two Primary Germ-layers. — Sensory Apparatus. — Constituentg of 
Sensory Apparatus : originally only the Exoderm, or Skin-layer; after- 
wards, the Skin-covering specialized from the Nerve-system. — Double 
Function of the Skin (as a Covering and as Organ of Touch). — Outer 
Skin (Epidermis) and Leather-skin (^Corium). — Appendages of the Epi- 
dermis : Skin-glands (Sweat-glands, Tear-glands, Sebaceous Glands, 
Milk-glands); Nails and Hair. — The Embryoaw Wool-covering. — Hair 
of the Head and of the Beard. — Influence of Sexual Selection. — Arrange- 
ment of the Nerve-system. — Motor and Sensory Nerves. — Central 
Marrow : Brain and Dorsal Marrow. — Constitution of the Human Brain : 
Large Brain {Cerehrtim) and Small Brain {Cerebellum). — Comparative 
Anatomy of the Central Marrow. — Germ-history of the Medullary- tube. 
— Separation of the Medullary-tube into Brain and Dorsal Marrow, 
— Modification of the Simple Brain-bladder into Five Consecutive Brain- 
bladders : Fore-brain (Large Brain, or Oerehrum), Twixt-brain ("Centre 
of Sight"), Mid-brain ('« Four Bulbs "), Hind-brain (Small Brain, or Qere. 
helium), After-brain (Neck Medulla). — Various Formation of the Five 
Brain-bladders in the various Vertebrate Classes. — Development of 
the Conductive Marrow, or ** Peripheric Nervous System." 

"Hardly any part of the bodily frame, then, could be found better 
oalculated to illustrate the truth that the structural diSerences between 
Mau and the highest Ape are of less value than those between the highest 



THE DEVELOPMENT OF THE OEGANS. I9I 

and the lower Apes, than the hand or the foot, and yet, perhaps, there is one 
organ which enforces the same conclusion in a still more striking manner — 
and that is the brain." — Ma/n*s Place in Nature, p. 94 (1863). 

"As if to demonstrate, by a striking example, the impoasibilitj of 
erecting any cerebral barrier between Man and the Apes, Nature has 
provided us, in the latter animals, with an almost complete series of gra- 
dations, from brains little higher than that of a Rodent to braim little lower 
than that of Man." — Ibid. p. 96. 



Our investigations, up to the present, have shown us how 
the whole human body has developed from an entirely simple 
beginning, from a single simple cell. The whole human 
race, as well as the individual man, owes its origin to a 
simple cell. The one-celled parent-form of the former is, even 
yet, reproduced in the one-celled germ-form of the latter. 
In conclusion, we must glance at the evolutionary history of 
the separate parts which constitute the human body. In 
this matter, I must, of course, restrict myself to the most 
general and important outlines ; for a detailed study of the 
evolutionary history of the separate organs and tissues 
would occupy too much space, and would demand a greater 
extent of anatomical knowledge than the generality of my 
readers are Likely to possess. In considering the develop- 
ment of the organs, and of their functions, we will retain the 
method previously employed, except that we will consider 
the germ-history and the tribal history of the various parts 
of the body in common. In the history of the evolution of 
the human body as a whole we have found that Phylogeny 
everywhere serves to throw light on the obscure course of 
Ontogeny, and that the clew afforded by phylogenetic con- 
tinuity alone enables us to find our way through the labyrinth 
of ontogenetic facts. We shall experience exactly the same 

fact in the history of the development of the separate 
46 



19a THE EVOLUTION OF MAX. 

organs ; but I shall be compelled to explain the ontogenetic 
and the phylogenetic origin of the organs simultaneously ; 
for the further we penetrate into the details of organic 
development, and the more minutely we study the origin 
of the separate parts, the more clearly do we see hour 
inseparably the evolution of the germ is connected with 
that of the tribe. The Ontogeny of the organs is intelligible 
and explicable only through their Phylogeny ; just as the 
germ-history of the entire body (the "person ") is rendered 
intelligible only by the history of the tribe. Each germ- 
form is determined by a con-esponding ancestral form. This 
is as true of the parts as of the whole. 

In endeavouring, with the help of this fundamental law 
of Biogeny, to obtain a general view of the main features in 
the development of the separate organs of man, we must, in 
the first place, consider the animal, and then the vegetative 
organ-systems of the body. The first main group of oigans, 
the animal organ-systems, is formed by the sensory apparatus, 
together with the motor apparatus. To the former belong 
the skin-covering, the nervous system, and the organs of the 
senses. The motor apparatus consists of the passive organs 
of movement (the skeleton) and the active organs (the 
muscles). The second main group of organs, the vegetative 
organ-system, is formed by the nutritive and the repro- 
ductive apparatus. To the nutritive apparatus belongs 
especially the intestinal canal with all its appendages, 
together with the vascular and renal systems. The repro- 
ductive apparatus includes the various sexual organs (the 
germ-glands, germ-ducts, organs of copulation, etc.). 

In earlier chapters (IX. and X.) it has been stated that 
the animal organ-systems (the instruments of sensation and 



AKIMAL AND VEGETATIVE ORGAN-SYSTEMS. 1 93 

of movement) proceed especially from the outer primary 
germ-layer, from the skin-layer. The vegetative organ - 
systems, on the other hand (the instruments of nutrition and 
reproduction), proceed principally from the inner primary 
{^erm-layer, from the intestinal layer. This radical contrast 
between the animal and the vegetative spheres of the body 
is, it is true, by no means absolute either in man or in the 
higher animals ; on the contrary, many separate parts of the 
animal apparatus {e.g., the intestinal nerve, or sympathetic) 
originated from cells which have proceeded from the ento- 
derm ; and, on the other hand, a large part of the vegetative 
apparatus {e.g., the mouth-cavity, and probably the greater 
part of the urinary and sexual organs) is formed of cells 
which are originally derived from the exoderm. Moreover, 
in the bodies of all the more highly developed animals, the 
most heterogeneous parts are so intermixed and blended 
that it is often extremely difficult to assign its true source 
to each one of the constituent parts. But, on the whole, we 
may assume as a certain and important fact, that in Man, 
and in all high animals, the greater part of the animal organs 
must be referred to the skiu-layer, or exoderm ; the greater 
part of the vegetative organs to the intestinal layer, or 
entoderm. For this reason, Baer called the former the 
animal germ-layer, the latter, the vegetative germ-layer 
(C£ vol. i. pp. 53 and 196). Of course, in making this important 
assumption, we pre-suppose the correctness of Baer's view, 
according to which the skin-fibrous layer (the "flesh 
stratum " of Baer) must have originated (phylogenetically) 
from the exoderm, and, on the other hand, the iutestinal- 
fibrous layer (Baer's "vascular layer") from the entoderm. 
This influential view, which is yet much disputed, is, we 



( 194 ) 



TABLE XXVI. 

Sjitematio Survey of the Organ- Systems of the Hnman Body. 

(N.B. — ^The origin of the separate organs from the four secondary germ, 
layers is indicated by the Roman numerals (I.-IV.) : I. Skin-sensory layer j 
II. Skin.fibrous layer ; III. Intestinal-fibrous layer ; IV. Intestinal-gland, 
alar layer.) 



H 
I 

o 



;z5 



Sensory 

Apparatus 

Sen$9ri%im 



'"1. Skin-covering 
(^Derma) 



( Outer skin 
I Leather skin 



■L 

Motive 
Apparatus 
Loeomoleritt 



a. Central nerve- ( Brain 

Bystem I Spihal marrow 

3. Periphericnerve- Jgf;y^^g7;^g"g 
system | Intestinal nervee 



4. Sense-orguu 
(^Orgcma semuwn) 



Mnscle • system 
(active motive- 
organs) 



/^ Organ of tonch (skin) 
Organ of taste (tongue) 
Organ of smell (nose) 
Organ of sight (eye) 

. Organ of hearing (ear) 



Skin muscles 
Skeleton mosclei 



Skeleton-system j Vertebral colamn 
(passive motive < Skull 
organs) ( Limb skeleton 



Epidermis, L 
Corium, II. 

Encephalon ^ j 

Medulla spinalis j 

Nervi cerebrales, I. + II 
Nervi spinales, II. 
Sympatheticus.II. + ILL 

Org. tactus 

Org. gustus 

Org. olfactus [• I. + 11 

Org. visus 

Org. audituB 



Mnsculi cutane 
M. skeleti 

Vertebrarium 

Cranium 

Sk. extremitatum 



n. 



H 

CO 

CO 
I 

< 

O 
» 

5 



c. 

Nutritive 
Apparatus 
Nutritorium 



''t. Intestinal system f Digestive organ 
(ftwter) \ Respiratory organ 



8. Vascular system 
(^Organa circv^ 
lationis) 



< Body cavity 
Lymph vessels 

Blood vessels 
Heart 






Reproductive 
Apparatus ^ 



9. Renal system J nH°f7v*H„^t. 



'Sexual glands 
(I. Ovary) 
(II. Testes) 
Sexual ducts 
(I. Oviduct) 



10. Sexual organs 



(n. Seed dBct) 



Copulatory oi 
^Sheath) 
(n. Penis) 



0. digestiva \„, ,y 
O.respiratoria/"^'*'^' 

Coeloma, II. + III. 
Vasa lympha- \ 

tica llL+IIL 

V. sanguifera I 
Cor, III. 

Urocystis, III. + lY. 



\ 



Gonades 

LOvaria)in, + IV.(?) 
II. Testes) L + U. (?) 

Gonophori » 

(I. Ovidac- I 
tus) U.(?)4'n 

(II. Spenua- 1 
dnctos) / 

Copulativa \ 

a.Tagina)W  n. 

(II. Penis) [ 



tHE SENSORY APPARATtTS. I$$ 

think, securely fomided on the Gastrula — that most impor- 
tant of all the germ-forms of the animal kingdom — which 
we find recurs in similar form in the germ-history of the 
most different classes of animals. This significant germ- 
form points unmistakably to a parent-form (the Gasti*aea) 
common to all animals, the Protozoa alone excepted ; in 
this long extinct parent-form the entire body of the animal 
consisted throughout life of the two primary germ-layers, as 
is yet the case, for a short time, in the Gastrula. In the 
Gastrsea the simple skin-layer did actually represent all the 
animal organs and functions, and the simple intestinal layer, 
on the other hand, all the vegetative organs and functions ; 
potentially, this is even yet the case in the Gastrula. 

In studying the development of the first important 
part of the animal sphere, the sensory apparatus, or sen- 
sorium, we shall now find how well adapted this Gastrsea 
Theory is to explain, not only in a morphological but 
in a physiological sense, the most important facts in the 
history of evolution. This sensory apparatus consists of two 
very distinct parts, having, apparently, nothing in common : 
in the first place, the external skin-coveiing {Derma), 
together with its appendages, the hair, nails, sweat-glands, 
etc. ; and, secondly, the nervous system, situated internally. 
The latter includes the central nervous system (brain and 
spinal chord), the peripheric brain-nerves and medullary 
nerves, and finally, the organs of sense. In the fully 
developed vertebrate body these two main constituents of 
the sensorium are entirely separate ; the skin lying entirely 
extemallv on the body, while the central nervous system 
is within, and quite separate from the former. The two 
are connected merely by a portion of the peripheric nerve- 



196 THE EVOLUTION OF MAN. 

system and of the sense-organs. And yet, as we already 
know from the germ-history of man, the latter is developed 
from the former. Those organs of our body which discharge 
the highest and most perfect functions of animal life — those 
of sensation, volition, thought — in a word, the organs of 
the psyche, of mental life — arise from the external skin- 
covering. 

This remarkable fact, considered in itself alone, seems so 
wonderful, inexplicable, and paradoxical, that the truth of the 
fact was simply long denied. The most trustworthy embryo- 
losfical oT3servations were met with the erroneous statement 
that the central nerve-system develops, not from the outer 
germ-layer, but from a special cell-layer lying underneath 
this. The ontogenetic fact would not, however, yield ; and, 
now that Phylogeny has thrown light on the subject, the 
fact seems perfectly natural and necessary. When we 
reflect on the historic evolution of mind and sense activities, 
we must necessarily conceive the cells, which accomplish 
these, as originally situated on the outer surface of the 
animal-body. Such externally placed elementary organs 
could alone directly receive and deal with impressions from 
the outer world. Afterwards, under the influence of 
natural selection, the complex cell-masses which had become 
especially " sensitive " gradually withdrew into the shelter of 
the interior of the body, and there laid the first foundations 
of a central nervous organ. As differentiation advanced, 
the distance and distinction between the external skin- 
covering and the central nervous system detached from this, 
became continually greater, and finally the two were per- 
manently connected merely by the conductive peripheric 
nervoa. 



DERMIC ORIGIN OF THE SENSORY ORGANS. 1 97 

This view is fully confirmed by the results of Comparative 
Anatomy. Comparative Anatomy shows that many lowei 
animals possess no nervous system, although, in common 
with higher animals, they exercise the functions of sensation, 
volition, and thought. In the Primitive Animals (Protozoa), 
which do not even form germ-layers, of course the nervous 
system, like the skin-covering, is wanting. Even in the 
second main division of the animal kingdom — in the Metazoa 
or Intestinal Animals — there is at first no nervous system. 
The functions of these are performed by the simple cell- 
layer of the exoderm, which the lower Intestinal Animals 
have inherited directly from the Gastraea (Fig. 209, e). This 
is the case in the lowest Plant Animals (Zoophyta), the Gas- 
trseads. Sponges, and the lowest Hydroid Polyps, which are 
but little higher than the Gastrseads. Just as all the vege- 
tative functions of these are performed by the simple intes- 
tinal layer, so all the animal functions are discharged by 
the equally simple skin-layer. The simple ceU stratum of 
the exoderm is, in these, skin-covering, motive apparatus, 
and nervous system simultaneously. 

Most probably the nervous system was also wanting in a 
large proportion of those Primitive Worms (Archelmintkes) 
which were developed directly from the Gastrseads. Even 
those Primitive Worms in which the two primary germ-layers 
had already split into the four secondary germ-layers (Plate 
V. Fig. 10), seem not to have possessed a nervous system 
distinct from the skin. The skin-sensory layer must, even in 
these long-extinct Worms, have been at once skin-covering 
and nerve-system. But already in the Flat Worms {Platel- 
minthes), and especially in the Gliding Worms (TurbeUaria) 
which of all existing forms approach nearest to the Primitive 



198 



THE EVOLUTION OF MAN. 



Worms, we find an independent nerve-system, distinct and 
separate from the outer skin-covering. This is the " upper 






Fig. 209. — Gastrnla of Gastrophysema (Gastraead-class). 

Fio. 210. — Transverse section through an embryonic Earth-worm : hs, 
skin-sensory layer; ^m, skin-fibrons layer; (?/, intestinal-fibrous layer; dd, 
intestinal-glandular layer ; a, intestinal cavity ; c, body-cavity, or Coeloma ; 
^^, nerve-ganglia; u, primitive kidneys. 

Fig. 211. — A Gliding Worm (Rhahdoccelum). From the brain or upper 
throat ganglion (g) nerves (n) radiate towards the skin (/), the eyes (au), 
the organ of smell {no), and the mouth (in) : h, testes; e, ovaries. 



THE SKIN. 199 

throat ganglion," situated above the throat (Fig. 211, gr ; Plate 
V. Fig. 11, m). The complex central nervous system of all 
higher animals has developed from this simple rudiment. 
In the higher Worms, e.g., the Earth-worms, according to 
Kowalevsky, the earliest rudiment of the central nervous 
system (Fig 210, n) is a local thickening of the skin- 
sensory layer (Jis), which afterwards becomes entirely 
detached from the horn-plate. Even the medullary tube of 
Vertebrates has the same origin. From the germ-history 
of Man, we already know that this medullary tube, the 
commencement of the central nervous system, originally 
develops from the outer skin-covering. 

Let us now turn aside from these very interesting 
features in evolution, and examine the development of the 
later human skin-covering, with its hairs, sweat-glands, etc. 
Physiologically, this outer covering (derma, or tegumentwm) 
plays a double part. The skin, in the first place, forms the 
general protective covering (integumentum commuTie) which 
covers the whole surface of the body, and protects all other 
parts. As such, it, at the same time, effects a certain ex- 
change of matter between the body and the surrounding 
atmospheric air (perspiration or skin-breathing). In the 
second place, the skin is the oldest and most primitive 
sense-organ, the organ of touch, which effects the sensation 
of the surrounding temperature and of the pressure or re- 
sistance of bodies with which it comes in contact. 

The human skin, like that of all higher animals, consists 
essentially of two distinct parts ; of the outer-skin, and of 
the underlying leather-skin. The outer-skin (epidermis) 
consists only of simple cells, and contains no blood-vessels 
(Fig. 212, ah). It develops from the first of the secondary 



200 



THE EVOLUTION OF MAN. 



germ-layers from the skin-sensory layer, and, directly, from 
the horn-plate of the latter. The leather-skin (corium), on 
the contrary, consists principally of connective or fibrous 




Ftq. 212.— Human skin 

in [.erpendicular section 
(aft CI Kcker), much en- 
lar'_re<.i : a, horuy stratum of 
uuLrt rkin (epidermiti) ; 6, 
tuucuus stratum of outer- 
skin ; c, papillae of the 
leather-skin (corium) ; d, 
biuud- vessels of the latter; 
e, /, excretory ducts of the 
sweat-ijlands (p) ; h^ fat- 
globules of the leather-skin ; 
i, nerve, passing above into 
a touch -body. 



tissue, contains numerous blood-vessels and nerves, and has 
a different origin. It develops from the outer stratum of 
the second secondary germ-layer, from the skin-fibrous layer. 
The leather-skin is much thicker than the outer-skm. In 
its deeper part, the " aubcutis," lie many masses of fat-cells 
(Fig. 212, h). Its upper part, the true " cutis," or papillary 
layer, forms, over nearly the whole surface of the body, a 
number of microscopic cone-shaped warts, or papillae, which 
fit into the overlying epidermis (c). These touch-warts, or 
sensory papillge, contain the most delicate of all the sensory 
organs of the skin, the " corpwscula tactius" Other papillae 



STRUCTURE OF THE SKIN. lOI 

contain merely the terminal loops of the nutritive blood- 
vessels of the skin {cd). All these different parts of the 
leather-skin originate, by differentiation, from the cells, origi- 
nally homogeneous, of the leather-plate, the outer lamella 
of the skm-fibrous layer (Fig. 112,Aj>r, vol. i. p. 352; Plates lY. 
and v., I', Figs. 65-69, hf, p. 277).^^^ 

Analogously, all the constituent parts and appendages ot 
the outer-skin (epidermis) origmate, by differentiation, from 
the homogeneous cells of the horn-plate (Fig. 213). At a 



Fig. 213. — Cells of the outer-skin {epidermis) of 
a human embryo of two months. (After KoelUker.) 



very early period, the simple cell-layer 
of this horn-plate splits into two dis- 
tinct strata. The inner, softer stratum 
(Fig. 212, h) is called the mucous layer; 
the outer, harder stratum (a), the horn-layer of the outer- 
skin. The surface of this horn-layer is continually worn 
out and thrown off; new cell-strata, produced by the 
growth of the underlying mucous layer, take its place. 
Originally the outer-skin forms an entirely simple cover 
over the surface of the body. Afterwards, however, sundry 
appendaojes develop from this both internally and ex- 
temall3\ The internal appendages are the skin-glands; 
the sweat-glands, the sebaceous glands, etc. The external 
appendages are hair, nails, etc. 

The glands of the skin-covering are at first merely 
solid plug-shaped growths of the outer-skin {epidermis), 
which penetrate into the underlying leather-skin (corium) 
(Fig. 214 1 ). A canal afterwards forms inside these solid 




202 



THE EVOLUTION OF MAN. 



plugs (2, 3), either owing to the softening an breaking 
up of the central cells, or as the result of a fluid internally 
secreted. Some of these skin-glands remain unbranched, as, 
for instance, the sweat-glands (e, / g). These glands, which 
secrete the sweat, are of great length, their ends forming a 
coil ; they :evor branch, however ; and the same is to be 
said of the glands which secrete the fatty wax of the ears. 




Fig. 214. — Kudiments of tcar-glands 
from a human embryo of four monthco 
(After Koelliker.) 1. Earliest I'udiment the 
shape of a simple, solid ping. 2 and 3. Fur- 
ther developed rudiments, which branch 
and become hollow : a, a solid offshoot ; 
e, cell- covering of the hollow offshoot ; /, 
rudiment of the fibrons covering, which 
afterwards forms the leather- skin round 
the glands. 

Most other skin-glands give out 
shoots and branches, as, for in- 
stance, the tear-glands, situated 
on the upper eyelid, which secrete 
the tears (Fig. 214), and also the 
sebaceous glands, .. aich produce the fatty sebaceous matter, 
and generally open into the hair-follicles. The sweat 
and sebaceous glands occur only in Mammals. The tear- 
glands, on the contrary, are found in all the three classes of 
Amnion Animals, in Reptiles, Birds, and Mammals. They 
are not represented in the lower Vertebrates. 

Very remarkable skin-glands, found in all Mammals, 
and in them exclusively, are the milk-glands (glandulcB 
mammales, Figs. 215, 216). They supply milk for z. r 
nourishment of the new-born Mammal. Notwithstandino; 



SKIN-GLANDS. 



203 



their extra^ordinary size, these important organs are merely 
large sebaceous skin-glands (Plate V. Fig. 16, md). The 
milk is produced by liquefaction of the fatty milk-cells 
within the branched milk-giand pouch (Fig. 215, c), just 
as the sebaceous matter of the skin, and the fatty matter 
of the hair are produced by the breaking up of fatty 
sebaceous cells within the sebaceous skin-glands. The 
excretory passages of the milk-glands enlarge into sac-like 
milk-ducts (b), which again become narrower (a), and open, 
through from sixteen to twenty-four minute apertures, into 
the nipple of the breast. The first rudiment of this large 
and complex gland is a very simple conical plug in the 





FiQ. 215. — The breast of the female in section : c, grape-like glandular 
lobules ; h, enlarged milk-ducts ; a, narrow excretory ducts, opening through 
the breast-nipple. (After H. Meyer.) 

Fig. 216. — Milk-glands of a new-bom child : a, original central gland 
2?j ema-Uer, and c, larger branches of the latter. (After Langer.) 



204 THE EVOLUTION OF MAN. 

outer-skin (epidermis), which extends into the leather-skin 
(coriwm), and there branches. In the new-bom child it 
consists merely of from twelve to eighteen radiating lobules 
(Fig. 216). These gradually branch, the excretory passages 
become hollow, and a large quantity of fatty matter collects 
between the lobules. Thus is developed the prominent 
breast of the female (mamma), on the summit of which 
rises the nipple (onam.m.illa), adapted for being sucked.^®^ 
The nipple does not appear until after the milk-gland 
is already formed; this ontogenetic phenomenon is very 
interesting, because the more ancient Mammals (the parent- 
forms of the entire class) had no nipples. In them, the milk 
simply emerged through a plane, sieve-like perforated spot 
in the abdominal skin, as is even now the case in the lowest 
extant Mammals, the Beaked Animals (Monotremata ; p. 146). 
On account of this character these animals may be called 
Am/ista (without nipple). In many of the lower mammals 
there are numerous milk-glands, situated at various points of 
the ventral side. In the human female there is usually only 
a pair of milk-glands, placed on the point of the breast, as in 
A.pes, Bats, Elephants, and some other Mammals. Occasion- 
ally, however, even in the human female two pairs of breast 
glands (or even more) appear, lying one behind the other ; 
this must be regarded as a reversion to an older parent- 
form. Sometimes these glands are well developed even in 
the male, and are capable of being sucked, though as a rule 
they exist in the male sex only as rudimentary organs with- 
out function. 

Just as the skin glands originate as local growths of 
the outer skin in an inward direction, so the appendages 
of the skin, called hair and nails, originate as local growths 



KXTERKAL APPENDAGES OF THE SKIK. 20$ 

of the outer skin in an outward direction. The nails (un- 
gues), which are important protective formations over the 
hind surface of the most sensitive parts of our limbs — the 
tips of the fingers and toes — are horny products of the 
epidermis, common to us with the Apes. In their place, 
the lower Mammals generally possess claws, and the 
Hoofed Animals (Ungulata) hoofs. The parent-form of 
Mammals undoubtedly had claws, such as appear in a 
rudimentary state in the Salamander. The hoofs of the 
Hoofed Animals and the nails of Apes and of Man originated 
from the claws of more ancient Mammals. In the human 
embryo the first rudiment of the nails first appears (between 
the horn-layer and the mucous layer of this outer skin) 
in the fourth month. Their edges do not, however, project 
until the end of the sixth month. 

The most interesting and important appendages of the 
outer skin are the hairs, which, on account of their peculiar 
structure and mode of origin, must be regarded as very 
characteristic of the whole Mammalian class. Hairs, it is 
true, appear widely distributed in many lower animals, e.g., 
in Insects and Worms. But these hairs, like those of plants, 
are thread-like processes of' the outer surface, and differ 
from Mammalian hairs in their characteristically finer 
structure and in their mode of development. Hence Oken 
rightly called Mammals "hairy animals." The hairs of 
Man, as of all other Mammals, consist simply of epidermic 
cells peculiarly differentiated and arranged. In their first 
state, they appear in the embryo as solid plug-shaped pro- 
cesses of the epidermis which penetrate into the underlying 
leather-skin (corium), as do the sebaceous and the sweat 
glands. As in the latter, the simple plug consists oiiginally 



206 THE KVOLUTION OF MAK. 

of th« ordinary epidermic cells. Within this a firmer 
central cellular mass of conical shape soon forms. This 
increases considerably in length, detaches itself from the 
surrounding cellular mass, the " root-sheath," and finally 
makes its way to the outside, appearing above the outer 
surface as a hair-stem. The deepest part, buried in the 
skin, the hair follicle, is the root of the hair, and is sur- 
rounded by the root-sheath. In the human embryo the 
first hairs make their appearance at the end of the fifth 
or in the beginning of the sixth month. 

During the last three or four months before birth the 
human embryo is usually covered by a thick coating of deli- 
cate woolly hairs. This embryonic wool-covering (lanugo) 
is often lost during the last weeks of embryonic life, and, 
at any rate, soon after birth, when it is replaced by the 
thinner permanent hair-covering. These later permanent 
hairs grow out of hair follicles which are developed from 
the root-sheaths of the deciduous woolly hair. In the 
human embryo, the embryonic woolly hair usually covers 
the entire body, with the exception of the palms of the 
hands and the soles of the feet. These parts remain bare, 
just as in all Apes and most other Mammals. Not un- 
frequently the woolly coat of the embryo differs considerably 
in colour from the later permanent hairy covering. Thus 
for instance, it sometimes happens in our own Indo-Ger- 
manic race that fair-haired parents are shocked to find 
their children, at their first appearance, covered by a dark 
brown, or even black, woolly covering It is only after this 
has been shed, that the parmanent fair hair, which the 
child inherits from its parents, makes its appearance. 
Occasionally the dark hair is retained for several weeksj 



THE HAIB Ifl A BUDBIENTARY ORGAH. 207 

or even months, after birth. This remarkable woolly 
covering can only be explained as an inheritance from our 
primordial long-haired ancestors, the Apes. 

It is equally worthy of note that many of the highei 
Apes resemble Man in the thin coat of hair which coveii 
certain parts of their body. In most Apes, especially in 
the higher Catarhines, the face is nearly or even quite bare, 
or is covered with hairs as thin and as short as those of 
Man. In these Apes also, just as in Man, the hair on the 
back of the head is usually distinguished by its length, 
and the males often have much beard and whisker. (Cf. 
Fig. 202, p. 175). In both cases this masculine adornment 
has been acquired in consequence of sexual selection. 
In some Apes the breast and the inner sides of the joints 
are very thinly covered with hair — far less abundantly than 
is the back and the outer sides of the joints. On the other 
hand, we not unfrequently see the shoulders, the back, and 
the outer sides of the limbs thickly covered with hair in 
men of Indo-Germanic or Semitic race. It is a well-known 
fact that in some families abundant hair on the body is 
hereditary, as is the relative vigour and character of the 
hair-growth of the beard and head. These great differences 
in the total and partial hairiness of the body, which appear 
very striking not only when we compare different races of 
man, but even when we compare many families belonging 
to the same race, are very simply explained by ihe fact 
that the entire hairy covering of Man is a rudimentary 
organ, an unused inheritance, which has been transmitted 
from the more hirsute Apes. In this matter, Man resembles 
the Elephant, Rhinoceros, Hippopotamus, Whale, and other 

Mammals of various orders which have also entirely or 

47 



208 THE EVOLUTION OF MAN. 

partially lost thoir origmal coat of hair in consequence of 
adaptation.^^ 

The form of Adaptation which has degraded the growth 
of hair on most parts of the human body, while preserving 
it, or even greatly developing it, on certain parts, was, in all 
probability, sexual selection. As Darwin has very clearly 
shown in his work on " The Descent of Man," sexual selec- 
tion has had especially great influence in this respect. In 
consequence of the male Anthropoid Apes, in selecting a 
partner, .preferring those females which were least hairy, 
and in consequence of the females preferring those suitors 
which were distinguished by peculiarly fine beard or head- 
hair, the general hirsuteness of the body was gradually 
degraded, while the beard and the hair of the head were 
advanced to a higher degree, of perfection. Climatic con- 
ditions, and other circumstances unknown to us, may, 
however, also have promoted the loss of the hairy coat. 

In proof of the assertion that the hairy covering of 
Man is directly inherited from the Anthropoid Apes, we 
find, according to Darwin, a curious evidence in the direc- 
tion, otherwise inexplicable, in which the rudimentary 
hairs lie on our arms. Both on the upper and on the 
lower arm the hairs are directed towards the elbow, where 
they meet at an obtuse angle. Except in Man, this striking 
arrangement occurs only in the Anthropoid Apes, the Gorilla, 
Chimpanzee, Orang, and several species of Gibbons. In 
other Gibbons the hairs of both the lower and the upper arm 
are directed towards the hand, as in other Mammals. This 
remarkable peculiarity of Anthropoids and of Man. can 
only be explained on the assumption that our common ape- 
like ancestors were accustomed, as they are eyen now, 



THE NERVOUS SYSTEM. 209 

during rain, to bring their hands together over their heads, 
or over a branch overhanging their heads. The reverse 
direction of the hairs, when the arms were in this position 
caused the rain to run off. Thus, even yet, the direction 
of the hairs on our lower arm testifies to this advantageous 
habit of our Ape-ancestors. 

If the skin and its appendages are minutely examined, 
Comparative Anatomy and Ontogeny supply many similar 
important "records of creation," showing that they are 
directly inherited from the skin-covering of the Ape. We 
obtained our skin and hair by inheritance, immediately 
from Anthropoid Apes, these from the lower Apes, which, 
in turn, inherited the same parts from lower Mammals. 
This is also true of the other great organ-system which 
is developed from the skin-sensory layer — of the nervous 
system and the sensory organs. This very highly developed 
organ system, which performs the highest vital functions^- 
those of the mind — we have inherited immediately from 
the Apes, and mediately from Mammals of a lower order. 

The human nervous system, like that of all other 
Mammals, is, in its developed condition, a very complex 
apparatus, the anatomical arrangement and the physiological 
activity of which may, in general terms, be compared to a 
telegraph system. The central marrow (medulla), or cen- 
tral nervous system, represents the principal station, the in- 
numerable "ganglion cells" (Fig. 7, vol. i. p. 129) of which are 
connected with each other and with numerous very delicate 
conducting lines by their branched processes. The latter 
are the peripheric " nerve fibres," distributed over the whole 
surfeice of the body; these, together with their terminal 
apparatus, the sense-organs, etc., constitute the " conductive 



2IO 



THE EVOLUTION OF MAN. 






marrow/' the peripheric nerve-system. Some, as sensory 
nerve-fibres, convey the sensations of the skin and of other 
sense-organs to the central medulla ; others, as motor nerve- 
fibres, transmit the impulses from the central marrow to the 
muscles. 



Fig. 217. — Huinan embryo 
of three months, in natural 
size, seen from the dorsal side ; 
the brain and dorsal marrow 
exposed (after Koelliker) : }i, 
hemispheres of the cerebrum 
(fore-brain) ; m, "four-bulbs" 
(mid-brain) ; c, small brain 
(hind-brain, or cerehellum). 
Below the latter is the 
three -cornered "neck-medulla" 
(after-brain) . 

'Fig. 218. — Central marrow 
of a human embryo of four 
months, in natural size, seen 
from the dorsal side (after 
Koelliker) : h, large hemi- 
spheres; V, "four-bulbs;" c, 
small brain ; 'mo, neck-medulla. 
Below this the dorsal medulla 
marrow). 





The central nervous system, or central marrow (medulla 
centralis), is the actual organ of mental activities, in the 
stricter sense. Whatever view is taken of the intimate 
connection between this organ and its functions, it is, at 
least, certain that those of its special activities which we 
call sensation, volition, and thought, are in man, as in all 
the higher animals, inseparably connected with the normal 
development of this material organ. Hence we must neces- 
sarily take a deep interest in the history of the development 



TBI: CENTRAL MARROW. til 

of this organ. As it alone can give us the most important 
information as to the nature of our " mind," it commands 
our most earnest attention. For if the central marrow 
develops in the human embryo exactly as in the embryos 
of all other Mammals, then the development of the human 
mental organ from the same central organ of other Mammals 
and, more remotely, from that of lower Vertebrates, cannot 
be questioned. It is, therefore, impossible to dispute the 
enormous significance of these phenomena of development. 

In order to appreciate these rightly, a few words must 
first be said as to the general form and anatomical construc- 
tion of the developed central marrow in Man. Like the 
central nervous system of all other Skulled Animals {Cra- 
niota), it consists of two distinct parts : firstly, of the brain 
or the meduUa of the head (encephalon, or medulla ca- 
pitis), and, secondly, of the spinal marrow (medulla spi- 
nalis). The former is enclosed in the bony skuU, or " brain 
case," the latter in the bony vertebral canal, which is com- 
posed of a consecutive series of vertebrse, shaped like signet 
rings. (Cf. Plate V. Fig. 16, m.) From the brain proceed 
twelve pairs of head nerves, from the spinal marrow thirty- 
one pairs of medullary or spinal nerves for the remainder 
of the body. The spinal marrow, when examined merely 
anatomically, appears as a cylindrical cord with a spindle- 
shaped swelling in the region of the neck (at the last of the 
neck-vertebrse) and another in the Imnbar region (at the 
first lumbar vertebra, Figs. 217, 218). At the swelling at 
the throat the large nerves of the upper limbs pass ofi" from 
the spinal marrow, and those of the lower limbs from the 
swelling in the lumbar region. The upper end of the spinal 
marrow passes through the neck-marrow (medulla oblon- 



212 



THE EVOLUtlON OV MA^. 



gata) into the brain. The spinal marrow a])pears indeed to 
be a dense mass of nervous substance ; but along its axis 
passes a very narrow canal, which is continued in front 
into the larger cavities of the brain, and which, like those 
cavities, is filled with a clear fluid. 

The brain forms a considerable mass of nervous sub- 
stance, of very complex, minute structure, which occupies 




Fig. 219. — Hnman brain, 
Been from the lower side. 
(After H. Meyer.) Above (in 
front) is the large brain 
(cerebrum), with extensively 
branched furrows ; below (be- 
hind) is the small brain (cere- 
helium), with narrow parallel 
furrows. The Roman numbers 
indicate the roots of the twelve 
pairs of brain nerves in order 
from front to back. 



the gi-eater part of the skull-ca\aty ; it is roughly distin- 
guishable into two main parts — the large and small brain 
{cerehrum and cerebellum). The former is situated in 
front and over the latter, and its surface exhibits the well- 
known characteristic convolutions and furrows (Figa. 219, 
220). On its upper surface it is divided by a deep longi- 
tudinal slit into two lateral halves, the so-called "great 
hemispheres," which are connected by means of a bridge, or 
" cross-piece " {corpus callosum). A deep transverse fissure 
separates the large brain {cer^hrwm) from the small brain 



THE BRAIN. 



213 



{cerebellum). The latter is situated more posteriorly and 
inferiorly, and shows on its outer surface equally numerous 
furrows, which are, however, much "finer and more regular, 




I'O 



Fig. 220. — Hnman brain, seen fiom the left side. (After H. Meyer.) The 
furrows of the large brain are indicated by large, thick lines, those of the 
imall brain by finer lines. Below the latter the neck-marrow is visible, f^-p, 
frontal convolutions ; Ce. a Ce. p, central convolutions ; B, fissui'e of Eolan- 
ins; S, Sylvian fissure; T, temporal or pai-allel fissure; Pa, parietal lobe; An, 
the annectant convolutions^; PO, parieto-occipital fissure ; Su, supra-marginal 
csonvolution ; IP, intra-parietal fissure ; t, temporo-sphenoidal convolution. 

and between them are curved ridges (Fig. 219, lower part). 
The small brain is also divided into two lateral halves by a 
longitudinal furrow; these are the "small hemispheres," 
which are connected at the top by a worm-like cross-piece, 
the " brain- worm " (vermis), and at the bottom by a bridge 
{jponfis varolii ; Fig. 219, VI.). 

Comparative Anatomy and Ontogeny show, however, that 
In Man, as in all other Skulled Animals, the brain originally 
consists not of two but of five distinct parts lying one 
behind another. These originally appear in the embryo of all 



214 THE EVOLUTION OF MAN. 

Skulled Animals (Craniota), from the Cyclostomi and Fishes 
up to Man, in exactly the same form, as five bladders 
placed one behind the other. Alike in their first rudiments, 
they, however, difier in their further development. In Man 
and all higher Mammals the first of these five bladders, the 
fore-brain, develops so excessively that, when mature, it 
forms, both in size and weight, by far the greater part of the 
whole brain. To it belong, not only the great hemispheres, 
but also the bridge (corpus callosum), which connects these 
two, the olfactory lobes, from which proceed the nerves of 
smell, and most of the processes lying on the roof and floor 
of the great lateral cavities of the two hemispheres ; such, 
for instance, as the large streaked bodies (corpora striata). 
On the other hand, the "centres of sight," which lie be- 
tween the streaked bodies, belong to the second main part, 
which develops from the twixt-brain ; and to the same part 
belong the third brain ventricle (which is single) and the 
processes known as the "funnel" (infundihulum), the 
gray mass, and the " cone " (conarium). Behind these, and 
between the large brain and the small brain, we find a little 
mass, composed of two pairs of bosses, and called the " four 
bulbs," on account of two superficial furrows which cross 
each other at right angles, thus quartering the whole mass 
(Figs. 217, m, 218, v). Though these " four bulbs " are very 
insignificant in Man and the higher Mammalia, they 
constitute a distinct part of the brain, the third, or mid- 
brain, which is, on the contrary, especially well developed 
in the lower Vertebrates. The next or fourth part of the 
brain is the hind-brain, or small brain (cerebellum), in the 
strict sense of the term, with its single middle process, 
the " wonn " (vermis), and its two lateral parts, the " small 



PAKTS OF THE BRAIN. 21$ 

hemispheres ^ (Figs. 217, c, 21 8, c) . Behind this comes, finally, 
the fifth and last part, the " neck-marrow " (medulla oblon- 
gata, Fig. 218, mo), which includes the single fourth Inain 
ventricle and the adjoining processes (pyramids, olives, and 
restiform bodies). The neck medulla passes directly down 
into the spinal marrow. The narrow central canal of the 
spinal marrow extends into the wider " fourth ventricle " of 
the neck medulla, which is rhomboidal in shape, and the 
floor of which forms the "rhomboid groove." From this 
proceeds a narrow duct, called the " aqueduct of Sylvius," 
which leads through the " four-bulbs " into the third ven- 
tricle, situated between the two "centres of sight;" and 
this cavity in turn is connected with the pair of lateral 
cavities which lie right and left in the large hemispheres. 
All the cavities of the central marrow are, therefore, directly 
connected together. Individually all these parts of the brain 
which we have enumerated have an infinitely complex, 
minute structure, which we cannot now study, and which 
hardly bears on our subject. This wonderful brain-struc- 
ture, as it occurs only in Man and the higher Vertebrates, is 
of the highest importance, simply because, in all Skulled 
Animals (Craniota), it develops from the same simple rudi- 
ments, from the five brain-bladders already enumerated. 
(Cf. Plates VI. and VII.) 

Before we direct our attention to the individual develop- 
ment of the complex brain from this series of simple 
bladders, we will, in order' to understand the matter more 
clearly, glance for a moment at those lower animals which 
have no such brain. Even in the skull-less Vertebrates, in 
the Amphioxus, there is no real brain. In this case the 
whole central marrow is merely a simple cylindrical cord 



2l6 THE EVOLUTION OF MAN. 

traversing the body longitudinally, and terminating in front 
almost as simply as at the other end : it is a simple medul- 
lary tube (Plate XI. Fig. 15, m). We found, however, that 
the rudiment of the same simple medullary tube occurs in 
the ascidian larva (Plate X. Fig. 5, m) and in the same cha- 
racteristic position, above the notochord. Moreover, when 
closely examined a small bladder-like swelling may be seen 
at the fore end of the medullary tube in these two closely 
allied animals ; this is the first indication of a separation of 
the medullary tube into brain (mj) and spinal marrow (m,). 
When,, however, we consider the undeniable relationship of 
the Ascidia to the rest of the Worms, it is evident that the 
simple central marrow of the former exactly answers to the . 
simple nerve-ganglion which, in the lower Worms lies above 
the throat (jpharynx), and which has, therefore, long been 
■called the "upper throat ganglion " (ganglion pharyngeum 
miperius). In the Gliding Worms (Turhellaria) the whole 
nerve system consists merely of this simple ganglion, which is 
situated on the dorsal side of the body, and from which nerve- 
threads radiate to the difierent parts of the body (Fig. 211,gn) 
This upper throat ganglion of the lower Worms is evidently 
the rudiment from which the more complex central marrow 
of the higher animals has developed. An elongation of the 
upper throat ganglion along the dorsal side gave rise to 
the medullary tube, which is characteristic of Vertebrates 
and the young forms of Ascidia alone. On the other hand, 
in all other animals, the central nerve system has de- 
veloped in a very different manner from the upper throat 
ganglion; in Articulated Animals {Arthropoda) especially, 
the latter has developed into a throat (pharyngeal) ring, 
with a ventral maiTow ; this is the case, also, in the articU' 



NERVOUS SYSTEM IK THE LOWER AinHAUL ^I^ 

* 

lated Ringed Worms {Annelida) and the Star-animals (Echi- 
noderraa), which originated from Arthropods. The Soft- 
bodied Animals (Mollusca) also have a throat ring, which is 
quite unrepresented in Vertebrates. Only in Vertebrates 
the central marrow developed along the dorsal side, while 
in all other animals which have been named it developed 
along the ventral side of the body.-^^ 

Descending below the Worms we find very many 
animals which are entirely without a nerve-system, and in 
which the functions of that system are performed simply by 
the outer skin-covering — by the cells of the skin-layer, or 
exoderm. This is the case in many low Plant Animals 
(Zoophyta), for instance, in all Sponges, and in the common 
fresh-water Polyp, the Hydra. It was also undoubtedly the 
case in all extinct Gastrseads. In all Primitive Animals 
{Protozoa) the nerve-system is, of course, unrepresented, for 
these have not as yet attained to the development of germ- 
layera 

In considering the individual development of the nerve- 
system in the human embryo, we must first of all start from 
the important fact already mentioned, that the first rudi- 
ment of the system is the simple medullary tube, which 
detaches itself from the outer germ-layer along the middle 
hne of the lyre-shaped primitive germ. We found (Figs. 
85-87, vol. i. p. 298) that the rectilineal primitive groove, or 
dorsal furrow, first arises in the centre of the lyre-shaped 
germ- disc. On each side of this rise the two parallel dorsal 
or medullary swellings. The free margins of these bend to- 
wards each other, coalesce, and form the closed medullary tube 
(Figs. 88-93, vol. i. pp. 800-309). At first this tube Hes directly 
under the horn-plate; it is, however, afterwards situate 



2lS 



THE EVOLUTION OF MAN. 




mff-~ 



EiGS. 221-223. — Lyre-shaped (or sole-shaped) germ-shield of a Chick, in 
three consecutive stages of evolution, seen from the dorsal surface : about 
twenty times enlarged. Fig. 221, with six pairs of primitive vertebrae. 
The brain a simple bladder Qib). The medullary furrow is wide open from 
the point x, very wide at z. mp, Marrow (or medullary) plates ; sp, side- 
plates ; y, boundary between the throat cavity (sh) and the head-intestine 
{vd). Fig. 222, with ten pairs of primitive vertebrae. The brain consists of 
three bladders : r, fore-brain; m, mid-brain ; /i, hind-brain, c, Heart ; dv, 
yelk-veins. The medullary furrow is wide open behind (z). wp, Marrow- 
plates. Fig. 223, with sixteen pairs of primitive vertebrae. The brain 
consists of five bladders : v, fore-brain ; z, twixt-brain ; m, niid-brain ; h, 
hind-brain ; n, after-brain, a, Eye-vesicles ; g, ear- vesicles ; c, heart ; dv, 
yelk- veins ; wp, marrow-plate, uw, primitive vertebrae. 



DEVELOPMENT OF THE BRAIN. 319 

quite internally, the upper edges of the primiti v^e vertebral 
plates, which penetrate, from right and left, in between the 
horn-plate and the medullary tube, uniting above the latter, 
and thus completely embedding it in a closed canal. As 
Gegenbaur most aptly remarks, " This gradual embedding 
in the interior of the body must be regarded as an incident 
acquired in connection with progressive differentiation, and 
with the consequent higher capacity, by which the most 
important organ of the system is secured in its interior." 

To every thoughtful and unprejudiced man it must 
appear an extremely important and pregnant fact, that our 
mental organ, like that of all other Skulled Animals {Cra- 
iiiota), commences in the same way and in exactly the same 
simple form m which this organ remains for life in the 
lowest Vertebrate, the Amphioxus (vol. i. p. 420, Fig. 151; 
Plate XI. Fig. 15, m). In the Cyclostomi, that is, in the stage 
above the Acrania, the anterior extremity of the cylindrical 
iiieduUary tube begins to extend, at an early period, in the 
form of a pear-shaped bladder, which is the first distinct 
rudiment of a brain (Plate XI. Fig. 16, rrii). For the central 
medulla of Vertebrates thus first distinctly differentiates 
into its two main sections, the brain (rrii) and the spinal 
marrow (mj). The first faint indication of this important 
differentiation is discoverable in the Amphioxus, perhaps 
even in the Ascidian larva (Plate X. Fig. 5). 

The simple bladder-like form of the brain, which is 
retained for a considerable time in the Cyclostomi, also 
appears at first in all higher Vertebrates (Fig. 221, hh). In 
the latter, however, it soon disappears, in consequence of 
the separation of the simple brain-bladder, by transverse 
contractions of its circumference, into several consecutive 






220 THE EVOLUTION OF MAN. 

parts. Two of these contractions first appear, and con- 
sequently the brain forms three consecutive bladders (Fig. 

5 ^- * Figs. 224-226.— Central mar. 

row of human embryo in the 
seventh week, two cm. long. 
(After Koelliker.) Fig. 226, 
view of the whole embryo from 
the dorsal side ; the brain and 
dorsal marrow laid bare. Fig. 
225, the brain and upper part 
of the dorsal marrow from the 

left side. Fig. 224, the brain from above : v, fore-brain ; «, twixt-brain ; 

m mid-brain ; h, hind-brain ; n, after-brain. 

222, V, m, h). The first and third of these three primitive 
bladders then again separate by transverse contractions, 
each into two parts, and thus five consecutive bladder-like 
di^dsions are formed (Fig. 223 : cf. also Plate V. Figs. 
13-16 ; Plates VI. and VII., second cross-line). These five 
fundamental brain-bladders, which re-occur in the same form 
in the embryos of all the Skulled Animals (Craniota), were 
first clearly recognized by Baer, who understood their true 
importance and distinguished them, according to their rela- 
tive positions, by very appropriate names, which are still in 
general use : I., fore-brain (y) ; II., twixt-brain (0); IIL, mid- 
brain (m) ; IV., hind-brain (h) , and V., after-brain (n). 

In all Skulled Animals, from the Cyclostomi to Man, 
the same parts, although in very various forms, develop 
from these five original brain-bladders. The first bladder, 
the fore-brain (protopsyche, v), forms by far the largest part 
of the so-called " great brain " (cerebrum) ; it forms the two 
^eat hemispheres, the olfactory lobes, the streaked bodies 
(corpora striata), and the cross-piece (corpus callosum), 
together with the "arch" (fornix). From the second 



THE BRAIN IN SKULLED ANIMAL& 221 

bladder, the twixt-brain (deutopsyche, z,) proceed primarily 
the " centres of sight " and the other parts which surround 
the so-called "third brain- ventricle," also the "funnel" 
(infuTidibulum), the " cone " (conarium), etc. The third 
bladder, the mid-brain (mesopsyche, m), furnishes the small 
group of the " four bulbs," together with the " aqueduct of 
Sylvius." From the fourth bladder, the hind-brain (meta- 
psyche, h), the greater part of the so-called " little brain " 
(cerehellurn) develops ; the central " worm " (vermU), and 
the two lateral "small hemispheres." The fifth bladder, 
finally, the after-brain (epipsyche, n), forms the neck-. 
marrow, or the "elongated marrow" (medulla ohloTigata), 
together with the rhomboid groove, the pyramids, olives, etc. 
The very highest importance must certainly be ascribed 
to the fact, seen in Comparative Anatomy and Ontogeny, 
that the brain is originally formed in exactly the same way 
in the embryos of all Skulled Animals {Graniota)y from the 
lowest Cyclostomi and Fishes, to Apes and Man. In all, 
the first rudiment of the brain is a simple bladder-like 
expansion at the anterior extremity of the meduUary tube. 
In all, the five bladders are formed from this simple bladder- 
like expansion, and in all, these five primitive brain- 
bladders develop into the permanent brain, with its many 
complex anatomical arrangements, which afterwards appear 
in such extremely diverse forms in the various vertebrate 
classes. On comparing the mature brain of a Fish, an 
Amphibian, a Reptile, a Bird, and a Mammal, it is hardly 
conceivable that the several parts of these forms, so ex- 
tremely difierent, both internally and externally, may be 
traced back to one common condition. And yet, aU these 
various brains of Craniota have originated from exactly the 



222 



THE EVOLUTION OF MAN. 



same rudimentary form. We need only compare the em- 
bryos of these various classes of animals at corresponding 
stages of development, in order to assure ourselves of this 
fundamental fact. (C£ Plates VI. and VII., second cross- 
line.) 



'Ai 



\IV 





s... 



in,'- 



A 



Fig. 227. — Brains of three embryonic Skulled Animals in vertical longi- 
tudinal sections: A, of a Shark (Heptanchus) ; B, of a Snake (Coluber); C, of 
a Goat (Ca^ra) ; a, fore -brain ; fe, twixt-brain ; c, mid-brain ; d, hind-brain ; 
e, after-brain; s, px'imitive fissure of the brain. (After Gegenbaur.) 

Fig. 228. — Brain of a Shark (ScylUum) from the dorsal side : g, fore- 
brain ; h, olfactory bulbs of the fore -brain, which send the large olfactory 
nerves to the large nose capsules (o) ; d, twixt-brain ; h, mid-brain (behind 
it, the insignificant rudiment of the hind-brain) ; a, after-brain. (After 
Busch.) 

Fig. 229. — Brain and dorsal maiTow of a Frog : A, from the dorsal side ; 
B, from the ventral side ; a, olfactory bulbs, in front of the fore-brain (&) ; 
i, funnel at the base of the twixt-brain ; c, mid-brain ; d, hind-brain ; s, 
rhomboid groove in the after-brain ; m, dorsal marrow (very short in the 
frog) ; m', root-processes of the spinal nerves ; t, fibre at the end of the 
dorsal marrow. (After Gegenbaur.) 



CXnfPA&jLTIYE VIEW OF BRAIN DEVELOPMENT. 223 

A thorough comparison of the corresponding stages of 
development in the brain in the various Skulled Animals 
(Craniota) is very instructive. If it is applied to the whole 
series of skulled classes, the following extremely interest- 
ing facts soon become evident : in the Cyclostomi {Myxi • 
noidea and Petromyzontes), which, as we have seen, are 
the lowest and earliest Skulled Animals, the whole brain 
remains for life at a very low and primitive stage of 
development, through which the embryos of the other 
Skulled Animals pass very rapidly; the ^ve original 
sections of the brain are visible throughout life in an almost 
unmodified form. But even in Fishes, an essential and 
important transformation of the five bladders takes place ; 
it is evidently from the brain of the Primitive Fishes 
(Selachii ; Fig. 228), that, on the one side, the brain of the 
other Fishes, and on the other, the brain of the Amphibians 
and also of the higher Vertebrates, must be traced. In 
Fishes and Amphibians (Fig. 229), the central part, the 
mid-brain, and also the fifth section, the after-brain, are 
especially developed, while the first, second, and fourth 
sections remain far behind. In the higher Vertebrates, the 
exact reverse is the case, for in these the first and fourth 
sections, the fore and hind brains, develop pre-eminently ; on 
the other hand, the mid-brain remains very small, and the 
after-brain is also much smaller. The greater part of the 
" four-bulbs " is covered by the large brain (cerebrum) and 
the after-brain by the smaU brain {cerebellum). Even 
among the higher Vertebrates themselves, numerous grada- 
tions occur in the structure of the brain. From the Am- 
phibians upward, the brain, and with it the mental life, 
develops in two different directions, of which the one is 

48 



226 THE EVOLUTION OF MAN. 

the animal, thus proving that the higher mental activities, 
consciousness and thought, conscious volition and sensation, 
may be destroyed one by one, and finally entirely anni- 
hilated. If the animal thus treated is artificially fed, it 
may be kept alive for a long time ; for the nourishment of 
the entire body, digestion, respiration, the circulation of the 
blood, secretion, in short, the vegetative functions, are in 
no way destroyed by this destruction of the most important 
mental organs. Conscious sensation and voluntary motion, 
the capacity for thought and the combination of the various 
higher mental activities, have alone been lost. 

This fore-brain, the source of all these most wonderful 
nervous activities, reaches that high degree of perfection only 
in the higher Placental Animals (Placentalia) ; a fact which 
explains very clearly why the higher Mammals so far excel 
the lower in intellectual capacity. While the "mind" of the 
lower Placental Animals does not exceed that of Birds and 
Reptiles, we find among the higher Placentalia an uninter- 
rupted gradation up to Apes and Man. Accordingly, their 
anterior brains show surprising differences in the degree of 
perfection. In the lower Mammals, the surface of the great 
hemispheres (the most important part) is entirely smooth 
and even. The fore-brain, too, remains so small that it 
does not even cover the mid-brain above (Fig. 230). One 
stage higher, and this latter is indeed entirely covered by 
the excessive growth of the fore-brain ; but the hind-brain 
remains free and uncovered. At last, in Apes and in Man, 
the fore-brain covers the hind-brain also. A similar gradual 
advance may also be traced in the development of the 
peculiar furrows and protuberances which are so charac- 
teristically prominent on the surface of the large brain 



CONVOLUTIONS OF BRAIN. 227 

{cerebrum) of higher Mammals (Figs. 219, 220). If the 
brains of the various mammalian groups are compared with 
reference to these convolutions and furrows, it appears that 
theii gradual development is entirely proportionate with 
the development of the higher intellectual activities. Much 
attention has recently been devoted to this particular 
branch of the Anatomy of the brain, and very striking 
individual differences have been found even within the 
human race. In all human individuals distinguished by 
peculiar ability and great intellect, these swellings and 
furrows on the surface of the great hemispheres exhibit a 
much greater development than in common average men; 
while in the latter, again, they are more developed than in 
Cretins and others of unusually feeble intellect. There are 
also similar gradations in the internal structure of the fore- 
brain in Mammals. The great cross-piece {corpus callosunt), 
especiaJly, the bridge between the two great hemispheres, 
is developed only in Placental Animals. Other arrange- 
merts, for example, in the structure of the lateral cavities, 
which seem primarily to be peculiar to Men as such, re- 
appear only in the higher species of Apes. It was long 
believed that Man had some entirely peculiar organs in the 
great brain (cerebrum), which are wanting in all other animals. 
But close comparison has shown that this is not the case, 
but that rather the characteristic qualities of the human 
brain exist in a rudimentary state even in the lower Apes, 
and are developed to a greater or less degree in the higher 
Apes. Huxley, in his important and much-quoted book, 
" Evidence as to Man's Place in Nature " (1863), has shown, 
most convincingly, that within the Ape-series the differences 
in the formation of the brain are greater between the 



2J8 the EVOLtmON OF MAN. 

higher and lower Apes than between the higher Apes and 
Man. This statement is, indeed, equally true of all the 
other parts of the body. But the fact that it is true of the 
central marrow is especially important This does not 
become fully evident unless these morphological facts are 
considered in connection with the corresponding physio- 
logical phenomena; until we consider that every mental 
activity requires for its complete and normal exercise the 
complete and normal condition of the corresponding brain- 
structura* The extremely complex and perfect active 
phenomena within the nerve-ceUs, summed up in the word 
"mental life," can no more exist without their organs in 
the vertebrates, including man, than can the circulation of 
the blood without a heart or blood. As, however, the 
central marrow of Man has developed from the same 
medullary tube as in all other Vertebrates, so also must the 
mental life of Man have had the same origin. 

All this is of course true of the conductive marrow, or 
the so-called "peripheric nervous system." This consists 
of the sensitive nervous fibres which convey the impressions 
of sensation from the skin and the organs of the senses in 
a centripetal direction to the central marrow ; as well as 
of the motor nervous fibres, which, reversely, convey the 
movements of volition from the central marrow, in a cen- 
trifugal direction to the muscles. By far the greater part 
of these peripheric conductive nerves originates from the 
skin-fibrous layer, by peculiar local difierentiation of the 
rows of cells into the respective organs. 

The membranous coverings and blood-vessels of the 
central marrow are identical in origin with the greater part 
of the conductive marrow; these membranous coverings 



OBIQIN OF THE FUNCTIONS OF THE BRAIN. 229 

are the inner membrane (pia mater), the central membrane 
(meniTix arachnoides), and the outer membrane {dura 
mater). All these parts are developed from the skin-fibrous 
layer. 



TABLE XXVII. 

Ststkmatic Susvet of the most important Periods ih th« PHTLOonrr 

OP THE Human Skin-coverings. 

I. First Period : Skin of Gastrceads. 

The entire skin-oovering (including the nervons system, not yet differ- 
entiated from it) consists of one simple layer of ciliated cells (exoderm, or 
primary skin-layer); as it is at the present day in the gastrula of the 
Amphiozns. 

n. Second Period : Shin of Primitive Worma, 

The simple exoderm of the Gastraead has thickened and split into two 
distinct layers, or secondary germ-layers : the skin-sensory layer (rudiment 
of the horn-plate and nerve-system) and the skin-fibrous layer (rudiment of 
the leather skin (corium), the muscle-plate and the skeleton-plate. The 
skin is potentially both covering and nund. 

m. Third Period : Skin of Chordonia. 

The skin-sensory layer has differentiated into the horn-plate (epidermis) j 
and the central marrow (upper throat ganglia) separated from it j the latter 
elongates into a meduUary tube. The skin-fibrous layer has differentiated 
into the leather plate (corium) and, below this, the skin-muscular pouch (as 
in all Worms). 

rV. Fowrth Period : Skin of Acranick. 

The horn-plate yet forms a simple epidermis. The leather-plate ii fUly 
differentiated from the mnsole and skeleton plates. 



230 THE EVOLUTION OF MAJNT. 

V. Fifth Period : Skin of Cyelostoma. 

The onter-skin remains a simple, soft mucous layer of cells, but forma 
one-celled glands (cup-cells). The leather-skin (corivm) differentiates into 
cutis and suh-cutis. 

VI. Sixth Period : Skin of Prtmitive Fishes. 

The outer skin is still simple. The leather skin forms placoid soalei or 
small bony tablets, as in the Selachii. 

VII. Seventh Period : Skin of Amphibia, 

The outer skin differentiates into an outer hom-layer, and an inner 
mucous layer. The ends of the toes are covered with homy sheaths (first 
rudiments of^lslaws or nails). 

VIII. Eighth Period : Skin of Mammals. 

The outer skin forms the appendages characteristic of Mammals cmly ; 
hair, and sebaceous, sweat, and milk glands. 



TABLE XXVIII. 

Systematic Suevei of the most important Periods in the PHTLOoiirr 

OF THE Human Nervous System. 

I. First Period ; Medulla of QastroBods. 

The nOTve system is not yet distinct from the skin, and, together with 
the latter, is represented by the simple cell-stratum of the exoderm, or 
primary skin-layer; as it is at the present day in the gastrula of the 
AmphiozQS. 

n. Second Period : Medulla of Primitive Worms, 

The central nerve system is yet, at first, a part of the skin-sensory layer, 
and afterwards consists of a throat medulla, a simple nerve-ganglion lying 
above the throat ; as it is now in the lower Worms : the upper throat- 
ganglion. 



SXTBYEY OF HUKAN NEBYOUS SYSTEM. 33 1 

m. Third Period : Medulla of Qhordonia. 

The central nerve system consists of a simple mednllarj tnbe, an 
elongation of the upper throat ganglion, which ia separated from thn inteo- 
tine by a notoohord (chorda dorsaUs). 

lY. Fourth Period : Medulla ofAerania. 

The simple medullary tube differentiates into two parts : a head, and a 
cLsfTsal part. The head medulla resembles a small, pear-shaped, simple 
swelling (the primitive brain, or first rudiment of the brain) on the anterior 
oztremity of the long cylindrical spinal marrow. 

Y. Fifth Period : Medulla of CyclostonM, 

The simple, bladder-like radiment of the brain divides into flre oon- 
■eontiTe brain-bladders of simple straotnre. 

YI. SitBth Period : Medulla of Primitive Fishes, 

The five brain-bladders differentiate into a form similar to that now 
permanently retained by the Selachii. 

YII. Seventh Period : Medulla of Amphibia, 

The differentiation of the five brain-bladders progresses to that stmotnre 
which is now characteristic of the brain in Amphibia. 

^ Yin. Eighth Period : Medulla of Mammals. 

The brain attains the characteristic peculiarities distinctive of Mammals. 
The following may be distinguished as subordinate stages of development ; 
1, the brain of Monotremes ; 2, the brain of Marsupials j 3, the brain of 
Semi-apes; 4, the brain of Apes; 5, the brain of Mav^Ufca ApM| 4 the 
brain of Ape-men j and 7| the brain of Man. 



( «32 ) 



TABLE XXIX. 

Bjitematio Sxxrrej of the Evolution of the Skiii.ooTeriQg aad 

Nerve System. 

XXIX. A. Survey of the Evolntloii of the SMn-oovering. 



fUm 

(Derma, 

or 

nUegununitm) 



i Horn-layer of the outer 
skin 
(Stratum comeum) 
Mucous layer of the 
outer skin 
{Stratum mueoium) 



Leather-ekln 

{Corium) 

Product of the Skln- 

fibrous-Uyer 



Fibrous layer of the 
leather ekin 
{Cutis) 
Fatty layer of tne leather 
skin 

{SubeuHi) 



/Hair 
NailB 
Sweat glands 

ITear glands 
Sebaceous glands 
Milk glands 

/Connective tlsMN 
Fatty tissue 
Musciilar tissue' 
Blood-vessels 
Papillffi of taste 
nerves of 
leather skin 



azkl 
the 



XXIX. B. Sorvej of the Evolution of the Central Marrow. 



Central Marrow, 

or 

Central Nerve 
System 

(Psyche, or Medulla 
Centralit), 

Product of the 

Skin-sensory 

layer 



I. Fore-brain 
(FrotoptycAe) 



n. Twixt-braln 

(^Deutopsyche') 



{Great hemispheres 
Olfactory lobules 
Lateral chambers 
Streaked bodies 
Arch 
Ooee piece 

r Centre of sight 
I Third chamber of the 
< brain 
1 Pineal body 
I. Funnel 



rFour bulbe 



m. Mld-braln 



IV. Hind-brain 

{Metapsyche) 



After-brain 
{£^p8yche'^y 



r Small hemispheres 
A Brain worm 
(^ Brain bridge 

{Pjrramids 
Olives 
Restiform bodies 
Fourth chamber of the 
brain 



\TI. Dorsal Marrow Notoptyehe 



Eemifph(Brce eert b rt 

Lobi olf actor ii 

Ventriculi lateraXm 

Corpora striata 

F^nix 

Corpus ecMotum 

Tkalami optiei 
Ventriculus tertUu 

Conarium 
InfundibtUvm 

Corpus bigeminum 
Aqun'ductus Sylvii 
Pedunculi cerebri 

Eemisphara cerebeUi 
Vermis cerebelli 
Pom Varolii 

Corpora pyramiddlia 
Corpora oliraria 
Corpora resti/ormia 
Ventriculus quartus 



Mediulla spinaiiM 



Kednllary 
eoverings 
{Menifigm) 



^Enreloprng mem- (^ g^^ medullary eWn 
branes, with the Central medull.ry skin 
nutn ive blood- J 3 ^^^^ medullary skin 

I^'splill^ ^^ I <^^«^ ^ "^« ddn-fibro«8 U^) 



Pia mater 

Arachnoidea 
Dura mater 






CHAPTER XXI. 

DEVELOPMENT OF THE SENSE-ORGANS. 

Origin of the most highly Purposive Sense-organs by no Preoonoeivo<3 
Purpose, but simply by Natural Selection. — The Six Sense-organs and 
the Seven Sense-functions. — All the Sense-organs originally Developed 
from the Outer Skin-covering (from the Skin-sensory Layer). — Organs 
of the Pressure Sense, the Heat Sense, the Sexual Sense, and the 
Taste Sense. — Structure of the Organ of Scent. — The Blind Nose-pits 
of Fishes. — ^The Nasal Furrows change into Nasal Canals. — Separation 
of the Cavities of the Nose and Mouth by the Palate Roof. — Structure 
of the Eye. — The Primary Eye Vesicles (Stalked Protuberances from 
the Twixt-brain). — Inversion of this Eye Vesicle by the Crystalline 
Lens, separated from the Horn-plate. — Inversion of the Vitreous Body . 
— The Vascular Capsule and the Fibrous Capsule of the Eyeball. — Eye 
lids. — Structure of the Ear. — The Apparatus for Perception of Sound : 
Labyrinth and Auditory Nerve. — Origin of the Labyrinth from thf 
Primitive Ear Vesicles (by Separation from the Horn-plate). — Conduct 
ing Apparatus of Sound : Drum Cavity, Ear Bonelets, and Drum Meuj - 
brane. — Origin of these from the First GiU-opening and the Parte 
immediately round it (the First and Second Gill-aroh). — Eudimentai ; 
Outer Ear. — Eudimentary Muscles of the Ear-sheU. 

" Systematic Physiology is based especially upon the history of develop- 
ment, and unless this is more complete, can never make r%pid progress j for 
the history of development furnishes the philosopher with the materials 
necessary for the secure construction of a system of organic life. Hence 
anatoniical and physiological researches should be prosecuted more from th« 



234 THE EVOLUTION OF MAN. 

point of view of development than is now the case ; that is, we should study 
(»ach organ, each tissue, and even each function simply with the view of 
determining whence they have arisen." — Emil Huschke (1832). 



The sense-organs are undeniably among the most important 
and most interesting parts of the human body; through 
their activity alone we recognize the objects in the world 
around us. " Nihil est in intellectu, quod non prius fuerit in 
sensu." They are the true springs of our mental life. In no 
other part of the animal body can we point to such extremely 
delicate' aiid complex anatomical contrivances, co-operating 
for a definite physiological aim ; and in no other part of the 
body do these wonderful and very apt contrivances seem, at 
tirst, to indicate a premeditated creative design so conclu- 
sively. Hence it is that, in accordance with the received 
teleological view, it has been customary to admire the so- 
caUed " wisdom of the Creator " and the " purposive con- 
trivances of His Creation " especially in this matter. But 
on more mature consideration it will be observed that the 
Creator, according to this conception, does after all but play 
the part of an ingenious mechanic or of a skilful watch- 
maker ; just, indeed, as all these cherished teleological 
conceptions of the Creator and His Creation are based on 
bhildish anthropomorphism. 

We admit that at first sight this teleological explana- 
tion seems to afford the simplest and fittest interpretation 
of these very apt contrivances. If the structure and func- 
tions of the very highly developed sense-organs are alone 
regarded, it seems as though their origin is hardly explic- 
able except on the assumption of a supernatural creative 
act. But it is exactly on this point that the history of 



ORGANS OF SENSE. 23$ 

evolution proves most clearty that this received conception 
is radically false. The history of evolution convinces us that 
the highly purposive and admirably constituted sense organs, 
like all other organs, have developed without premeditated 
aim ; that they originated by the same mechanical process 
of Natural Selection, by the same constant interaction 
of Adaptation and Heredity, by which all the other pur- 
posive contrivances of the animal organization have been 
slowly and gradually evolved diuing the " Struggle for 
Existence." 

Like most other Vertebrates, Man possesses six distinct 
organs of sense, which accomplish seven distinct sensations. 
The external skin-covering accomplishes the sensation of 
pressure (resistance) and of temperature (warmth and cold). 
This is the earliest, the lowest, and the least differentiated 
organ of sense; it is distributed over the entire surface of 
the body. The other sensorial activities are localized. The 
sexual sense is limited to the skin-covering of the external 
sexual organs, just as the sense of taste is limited to the 
mucous membrane of the mouth-cavity (tongue and palate), 
and the sense of smell to the mucous membrane of the 
nose-cavity. Special mechanical contrivances of great com- 
plexity exist for the two highest and most differentiated 
organs of sense, the eye for the sense of sight, and the ear 
for that of hearing. 

Comparative Anatomy and Physiology show that in the 
low animals specialized sense-organs are entirely wanting, and 
that all sensations are transmitted through the outer surface 
of the skin-covering. The undifferentiated skin-layer, or exo- 
derm, of the Gastrsea is the simple cell-layer from which the 



236 THE EVOLUTION OF MAN. 

differentiated sense-organs of all Intestinal Animals (Jl/e^azoa), 
and, therefore, of aU. Vertebrates, originally developed. Start- 
ing from the consideration that necessarily only the most 
superficial parts of the body, those immediately exposed to 
the outer world, could have accomplished sensations, we 
should be justified in conjecturing d priori that the organs of 
sense also owe their origin to the same part. This is, indeed, 
the fact. The most important part of all sense-organs 
develops from the outermost germ-layer, from the skin- 
sensory layer ; in part, directly from the horn-plate, and, in 
part, from the brain, the foremost section of the medullary 
tube, after this has separated from the hom-plate. On 
comparing the individual development of the various organs 
of sense, we see that at first they make their appearance in 
the simplest conceivable form : only very gradually does 
that wonderful perfect structure develop by which the 
higher sense-organs eventually become the most remarkable 
and the most complex mechanisms of the entire organiza- 
tion. All organs of sense are, however, originally merely 
portions of the external skin-covering, in which sensorial 
nerves are distributed. Even these nerves were originally 
homogeneous and undifferentiated in character. Gradually, 
by division of labour, the various functions or " specific 
energies" of the different sensorial nerves developed Simul- 
taneously the simple terminal expansions of these sense 
nerves in the skin-covering developed into extremely com- 
plex organs. 

The important bearings of these historic facts upon the 
just appreciation of mental life will readily be perceived. 
Thfd whole philosophy of the future will assume another 



1 



NATUBAL SYSTEM OF PSYCHOLOGY. 237 

form as soon as Psychology has gained an accurate know- 
ledge of these genetic facts, and has made them the basis of 
its speculations. 

If the psychological teachings, published by the best- 
known speculative philosophers, and stUl generally received, 
are impartially studied, the simplicity with which the authors 
bring foi-ward their airy metaphysical speculations, regardless 
of all the significant ontogenetic facts by which theii 
doctrines are clearly refuted, cannot fail to causie great sur- 
prise. And yet the history of evolution, in conjunction 
with the rapidly advancing Comparative Anatomy and 
Physiology of the sense-organs, afibrds the only safe founda- 
tion for the natural theory of the mind. 

With reference to the terminal expansions of the 
sensory nerves, the human organs of sense may be distri- 
buted into three groups, corresponding to three different 
Btages of development. The first group includes those 
sense-organs, the nerves of which distribute themselves 
simply in the free surface of the skin-covering (organs of 
the sense of pressure, of heat, and of the sexual sense). In 
the second group, the nerves distribute themselves in the 
mucous membrane of cavities, which are originally grooves 
or inversions of the skin-covering (organs of taste and of 
smell). Finally, the third group is constituted by those 
very highly developed sense-organs, the nerves of which 
distribute themselves over an internal vesicle detached from 
the skin-covering (organs of sight and hearing). This 
remarkable genetic relation is represented in the following 
table : — 



a3» 



THE EVOLUTION OF MAN. 



Senur^ngant. 



o6flM-fKr0M. 



Sem^/uneticma. 



A* Sense-organs in 
which the ter- 
minal expansions 
of the nerves are* 
distributed in the 
outer akin-oorer. 
ing. 

B. Sense-organs in 
which . the ter- 
minal expansions 
of the nerves are 
distributed over 
inverted grooves 
of the outer skin. 
covering. 

0. Sense-organs in 
which the ter- 
minal expansions 
of the nerves are 
distributed over-' 
vesicles sepa- 
rated from the 
external skin. 
ooTering. 



I. Skin-covering 
(outer skin, or 
epidermis, and 
leather - skin, 
or corivm) 

n. External 
sexual parts 
(penis and eli- 
toria) 

m. Muoousmem- 
brane of the 
mouth - cavity 
(tongue and 
palate) 

IV. Mucous mem- 
brane of the 
nose-cavity 



V. Bye 
VI. Ear 



I. Skin nerves ) Sense of pressure 
(nervi cutcmei) i Sense of warmth 



II. Sexual nerves 3. Sexual senM 
(nervi pudendi) 



m. Taste nerve 
(nervus gloaso- 
pharyngev>8) 



TV. Olfactory 
nerve 
(n. olfactorius) 



4. SeoBO of taste 



6. Sense of smeU 



V. Sight nerve 6. Sense of sight 
{n. opticus) 

VI. Ear-nerve 7. Sense of hear- 
(n. acousticus) ing 



Of the developmental history of the lower organs of 
sense I have but little to say. The development of the skin- 
covering, which is the organ of the sense of pressure (sense 
of touch) and of warmth, we have already traced (p. 209). 
I need only add that in the leather skin (corium) of Man, 
as of aU higher Vertebrates, innumerable microscopic sense- 
organs develop, the direct relations of which to the sensa- 
tions of pressure or resistance, of warmth and of cold, are 
not yet ascertained. These organs, in or upon which the 
sensitive skin-nerves terminate, are the so-caUed "touch 
bodies " and the " Pacinian bodies/' named after their dis- 



MUCOUS MEMBRANE OF THE TONGUE AND NOSE. 239 

coverer, Pacini. Similar bodies are also found in the organs 
of the sexual sense, in the penis of the male and in the 
clitoris of the female ; these are processes of the integument, 
and the development of which we shall consider presently, 
in connection with that of the other organs of generation. 
The development of the organ of taste, the tongue and the 
palate, we will also consider presently, in connection with 
that of the intestinal canal, to which these parts belong. 
To one point, however, I 'vill now call particular attention, 
viz., the mucous membrane of the tongue and palate, in 
which the taste-nerv^ terminates, is also in its origin a portion 
of the external skin-covering. For, as we found, the entire 
mouth-cavity originates, not as a part of the actual intes- 
tinal canal, but as a groove-like inversion of the external 
skin (vol. i. p. 338). Its mucous membrane, therefore, is 
formed, not from the intestinal layer, but from the skin- 
layer, and the taste-cells on the upper surface of the tongue 
and palate arise, not from the intestinal-glandular layer, 
but from the skin-sensory layer. 

This is equally true of the mucous membrane of the 
organ of smell, the nose. The history of the development 
of this sense-organ is, however, of far higher interest. 
Although the human nose, externally viewed, seems oimple 
and single, yet in Man, as in all higher Vertebrates, it 
consists of two perfectly distinct halves, of a right and a left 
nasal cavity. These two cavities are entirely separated by 
a vertical partition, so that the passage into the right nasal 
cavity lies only through the right nostril, and into the left 
cavity only through the left nostril. Posteriorly the two 
nasal cavities open separately through the two posterior 

nasal apertures into the head of the pharynx, so that the 
49 



240 THE EVOLUTION OF MAN. 

pharynx may be entered without touching the cavity of the 
mouth. This is the passage by which air is usually inhaled; 
the mouth being shut, it enters the pharynx, and thence 
passes through the windpipe into the lungs. Both nasal 
cavities are separated from the mouth-cavity by the hori- 
zontal bony palate roof, to the back of which the soft 
palate and the uvula is attached, like a hanging curtain. 
In the upper and hinder portion of both nasal cavities the 
olfactory nerve extends over the mucous membrane, which 
lines these parts. This is the first pair of brain nerves, 
which issue from the skull-cavity through the sieve bone. 
Its branches extend partly over the partition waU, and 
partly over the inner side- walls of the nasal cavities, to 
which are attached the "shells," or spongy bones of the 
nose — complex bony structures. These " shells " are much 
further developed in many of the higher Mammals than 
in Man. In all Mammals there are three of these " shells " 
in each of the two nasal cavities. The sensation of smeU 
is produced by a current of air, containing odoriferous 
matters, passing over the mucous membrane of the cavities, 
and there coming in contact with nerve-ends. 

The peculiar characters which distinguish the olfactory 
organ of Mammals from that of lower Vertebrates, are 
represented in Man. In all specific points the human nose 
exactly resembles that of the Catarhine Apes, some of which 
indeed possess an entirely human external nose (see face 
of the Nose-ape, Fig. 202, p. 175). The first rudiment of thfl 
olfactory organ in the human embryo does not, however, 
show any signs of the fine form of the future catarhine 
nose. Indeed, it first appears in the same form which 
persists for life in Fishes , in the form of two simple pits, 



THE NOSK 



241 



or grooves in the skin of the upper surface of the head. In 
all Fishes two of these mere blind nose-pits are found in 
the upper surface of the head ; sometimes they are situated 
at the back, near the eyes, sometimes near the snout, or, 
again, near the mouth-opening (Fig. 191, 71, p. 113). They are 
lined by mucous membrane in folds, over vrhich the end 
branches of the olfactory nerves spread. 

In this its original condition the double nose of all 
Amphirhina (p. 101) is entirely unconnected with the pri- 
mitive mouth-cavity. "The connection, however, begins to 




7n 



Fig. 231.— Head of a Shark {Scyl- 
Hum), from the ventral side : m, mouth 
opening ; o, nose grooves, or pits ; r, 
nasal furrow; w, nose-flap in its 
natural position ; n', nose-flap turned 
up. (The dots are openings of mucous 
ducts.) (After Gegenbaur.) 



appear even in some Primitive Fishes (Selachii) ; a super- 
ficial skin-furrow extends on each side from the nose-groove 
down to the adjacent corner of the mouth. This furrow, 
the nasal channel, or furrow (Fig. 231, r), is of great sig- 
nificance. In many Sharks (e.g., Scyllium) a special process 
of the frontal skin, the nasal flap, or " inner nasal process," 
overlaps the nasal furrow (n, n'). Opposite to this the outer 
edge of the furrow rises and forms the "outer nasal process." 
In Dipncusta and Amphibia these two nasal processes meet 
over the furrow and coalesce, thus forming a canal, the 
" nasal canal." There is now a passage from the external * 
nasal groove tli rough this canal directly into the mouth- 



343 "^BX BVOLUnON OF MAN. 

cavity, which latter was developed independently of the 
groove. In the Dipneusta and the lower Amphibia the 
internal opening of the nasal canal lies well forward (behind 
the lips) ; in the higher Amphibia it Ues further back. In 
the three highest vertebrate classes, the Amniota, the 
primary mouth-cavity is separated by the formation of the 
horizontal palate roof into two perfectly distinct cavities, 
the superior (or secondary) nasal cavity, and the inferior 
(or secondary) mouth-cavity. The nasal cavity is also 
separated by the vertical partition into two distinct halves, 
into a right and a left nasal cavity. 

Comparative Anatomy thus still shows us simultaneously, 
in the ascending series of the double-nostrilled Vertebrates, 
from Fishes up to Man, all the various stages of develop- 
ment of the nose which the very highly developed olfactory 
organ of the higher Mammals has passed through svxices- 
sively in the different periods of its tribal history. The 
first rudiment of the organ of smell in the embryo of Man 
and in that of all the higher Mammals, makes its appearance 
in the same entirely f imple form which is retained throughout 
life by the nose of Fishes. At a very early stage, and 
while no trace of the characteristic facial structure of Man 
is yet visible, a pair of small grooves appear on the front 
of the head, and before the primitive mouth-cavity ; these 
were first discovered by Baer, and by him properly enough 
named *' olfactory grooves " (" Kiechgruben," Figs. 232, n, 
233, n). These primitive nasal grooves are quite separate 
from the primitive mouth-cavity, or mouth indentation, 
which, as we found, likewise makes its appearance as a 
groove-like indentation of the external skin-covering, in 
ftimi oi the l^iind anterior extremity of the intestinal caiiaL 



DEVELOPMENT OF THE NOSE. 



243 



This pair of nasal grooves, as well as the single mouth 
groove (Fig. 235, m), is lined by the horn-plate. The 




Fig. 232. 



a n 




Fig. 233. 



X. 




an 



-rp 




m 



inf 




■n f 



Fig. 235. 



Fig. 236. 



Figs. 232, 233.— Head of an embryonic Chick, on the third day of 
incubation : 232, from the front ; 233, from the right side, w, Nose-rudi- 
ment (olfactory grooves) ; I, eye-rudiment (sight-grooves) ; g, ear-rudiment 
(auditory grooves); -u, fore-brain ; gl, eye-slits ; o, upper jaw process; w, 
lower jaw process of the first gill arch. 

Fig. 234. — Head of an embryonic Chick, on the fourth day of incubation, 
from below: n, nose -groove ; o, upper jaw process of the first gill arch; 
y, lower jaw process of the same ; /c", second gill-arch; sp, choroidal fissure 
of the eye ; s, throat (pharynx). 

Figs. 235, 236. — Two heads of embryonic Chicks : 235, at the end of the 
fourth day ; 236, at the end of the fifth day of incubation. The letters as in 
Fig. 234. Additional letters are in, inner, and an, outer nasal process ; 7j/, 
nasal furrow ; st, frontal process ; m, mouth-cavity. (After Koelliker.) 

All these figures are proportionately enlarged. 



244 '™^ EVOLtJTIOK OF MAIT. 

original separation of the nasal groove from the mouth 
groove is, however, soon interrupted, for the frontal procesa 
(Fig. 235, st, Rathke's " Nasenfortsatz der Stirnwand ") 
is immediately formed above the mouth groove. Right and 
left the edges of this process project in the form of two 
lateral processes : these are the inner nasal processes, or 
nasal flaps (Fig. 235, in). On each side, opposite to these 
rises a parallel ridge between the eye and the nasal groove. 
These ridges are the outer nasal processes (Rathke's "Nasen- 
dacher," Fig. 235, an). Between the inner and outer 
nasal process a channel-like depression thus extends on 
each side from the nose groove toward the mouth groove 
(m), and this channel is, of course, the same nasal furrow 
or channel which we found in the Shark (Fig. 231, r). As 
the two parallel edges of the inner and the outer nasal 
processes bend towards each other and coalesce above the 
nasal channel, the latter becomes a small tube — the primitive 
" nasal canal." In this stage of its Ontogeny, therefore, the 
nose of Man and of all other Amnion Animals consists of 
two small narrow tubes — the " nasal canals " — leading from 
the outer surface of the frontal skin into the simple pri- 
mitive mouth-cavity. This transient condition resembles 
the permanent condition of the nose in Dipneusta and 
Amphibia. (Cf. Plate I., Frontispiece, with explanation.) 

Specially significant in the modification of the open nasal 
channel into the closed nasal canal, is a plug-shaped forma- 
tion, which extends from below up to the lower extremities 
of both the nasal processes on each side, and unites with 
them. This is the upper jaw process (Figs. 232, o, 236, o, 
Plate I., o). Below the mouth groove lie the gill arches, 
which are separated from one another by the gill openings 



UPPER JAW PROCESS. 345 

(Plates I., YI., and YII., k). The first of these gill arches, at 
present the most interesting to us, which we may call the 
jaw arch, develops the jaw-skeleton of the mouth (Plate I., u). 
A small process first grows out from the base of the front 
gill-arch : this is the upper jaw process. The first gill-arch 
itself develops a cartilage on its inner side, called after its 
discoverer, "Meckels cartilage," on the outer surface of 
which the lower jaw forms (Figs. 232, u, 236, u). The upper 
jaw process forms the principal part of the entire framework 
of the upper jaw, viz., the palate bone and the wing bone. 
On its outer side the upper jaw bone, in the narrower sense, 
afterwards arises, while the middle portion of the upper jaw 
skeleton, the twixt jaw (intermaxillary bone) develops 
from the anterior portion of the frontal process. (See 
development of the face in Plate I.) 

In the further characteristic development of the face in 
the three higher vertebrate classes, the two upper jaw pro- 
cesses are of the highest importance. From them proceeds 
the palate roof, the important horizontal partition which 
grows into the simple primitive mouth -cavity, separating 
it into two quite distinct cavities. The upper cavity, 
into which the two nasal cavities open, now develops into 
the nasal cavity — a respiratory air passage and an olfactory 
organ. The lower cavity, on the other hand, forms, by itself, 
the permanent secondary mouth-cavity (Fig. 237, w) — the 
digestive food passage and the organ of taste. Both the upper 
smell-cavity and the lower taste-cavity open at the back into 
the throat (pharynx). The palate roof, separating these two 
cavities, is formed by the coalescence of two lateral portions 
— of the horizontal plates of the two upper jaw processes 
(palate-plates ; Fig. 237, p). When these do not perfectly 




246 THE EVOLUTION OF MAN. 

adhere in the middle line, the result is a permanent longi- 
tudinal cleft, through which there is an open passage from 
the mouth-cavity^ directly into the nasal cavity. The so- 



FiG. 237. — Diagrammatic transverse section 
through the mouth and nose cavity. While the 
palate-plates (2^) separate the original mouth-cavity 
into the lower secondary mouth-cavity (m) and the 
upper nasal cavity, the latter is parted by the ver- 
tical partition wall of the nose (e) into two distinct 
halves {n, v). (After Gegenbaur.) 



called " wolf's jaws " are thus caused. The " hare-lip " and 
" split lip " is a slighter degree of this arrested develop- 
ment. ^^^ 

Simultaneously with the horizontal partition of the 
palate roof, a vertical wall by which the single nasal cavity 
is divided into two, a right and a left cavity, develops 
(Fig. 237, n, n). This vertical partition of the nose (e) is 
formed by the middle part of the frontal process : above 
this gives rise by ossification to the vertical lamella of the 
sieve bone (cubiform plate), and below tlie great vertical 
bony partition wall — the " plough -share " {fomei'), and in 
front to the twixt-jaw (os interTnaxillare). Goethe was 
the first to show that in Man, just as in all the other Skulled 
Animals, the twixt-jaw a^^pears as an independent bone 
between the two halves of the upper jaw. The vertical 
partition wall of the nose finally coalesces with the horizontal 
palate roof. The two nasal cavities are now as entirely 
separate from one another as from the secondary mouth- 
cavity. These three cavities open, however, at the back 
into the pharnyx, or jaw-cavity. 



THE HUMAN NOSE. 



247 



The double-nostrilled nose lias now attained the structure 
characteristic of Man in common with all other Mammals. 
Its further development is very easily intelligible : it is 
limited to the formation of internal and external processes 
of the walls of both nasal cavities. Within the cavities 
develop the " nose shells," spongy bony structures, over which 
the olfactory mucous membrane spreads. The first brain 
nerve, the olfactory nerve, with its delicate branches, passes 





Figs. 238, 239. — Upper part of the body of a human embryo (16 mm. in 
length) dm:ing the sixth week : Fig. 238, from the left side ; Fig. 239, from 
the front. The origin of the nose in two lateral halves, 
originally separate, is still plainly visible. The nose and 
upper lip are disproportionately great in comparison with 
the rest of the face, especially with the lower lip. 
(After Kollman.) 

Fig. 240. — Face of a human embryo of eight weeks. 
(After Ecker.) Cf. Frontispiece, Plate I. Fig. Mi— 
Mm. 




248 THE EVOLUTION OF MAN. 

from the large brain through the roof of both nasal cavities 
into the cavities, and extends over the olfactory mucous 
membrane. At the same time, by inversion of the nasal 
mucous membrane, the minor cavities of the nose, which are 
afterwards filled with air, and which communicate directly 
with the two nasal cavities, arise (frontal cavities, cavities of 
the sphenoid bone, jaw cavities, etc.). In this special stage 
of development they occur only in Mammals.^^ 

The external nose is not developed until long after all 
these essential internal parts of the olfactory organ have 
been formed. The first trace in the human embryo appears 
at the end of the second month (Figs. 238-240). Any 
human embryo during the first month shows that originally 
there is no trace of the external nose. It afterwards grows 
out from the anterior nasal portion of the primitive skull. 
The form of nose which is characteristic of Man does not 
appear till a period far later. Much stress is usually 
laid on the shape of the external nose as a noble organ, 
occurring exclusively in Man ; but there are Apes which 
have very human noses, as, for instance, the Nosed Ape 
already mentioned. On the other hand, the external nose, 
the fine shape of which is so extremely important to the 
beauty of the facial structure, possesses in certain inferior 
races of Man a shape anything but beautiful. In most 
Apes the external structure of the nose remains undeveloped. 
Especially remarkable is the important fact already cited 
that it is only in the Apes of the Old World, in the Cata- 
rhines, that the nasal partition wall (septum) remains as 
small as it is in Man ; in Apes of the New World it widens 
considerably at the base, so that the nostrils open outwards 
(Platyrhini, p. 175). 



( 249 ) 
TABLE XXX. 

STtTEMATIC SUBVKT 07 THE ChIEF FhYLOOENETIC StAGH OV TBB 

Human Nose. 

First Stage : Nose of the earlier rrimitive Fishes. 

'Hie nose is formed by a pair of simple skin-groores (nose-pits) in ike 
Mtter surface of the head (like those which are now permanently retained 
by the lower Selachians). 

Second Stage : Nose of the more recent Primitive Fishes. 

Each of the two blind nasal grooves becomes connected by a furrow 
(nasal-furrow) with one end of the mouth (as is yet permanently the case in 
khe higher Selachians). 

Third Stage : Nose of the Dipnmtsta. 

The two nasal furrows change, in consequence of the coalescence of their 
edges, into closed canals (primary nose-canals), which open at their front 
ends, within the soft edges of the lip, into the primary mouth-cavity; as is 
yet permanently the case in the Dipneusta and the earlier lower Amphibia 
{Sozohranchia). 

Fourth Stage : Nose of Amphibia. 

The inner openings of the nasal canals penetrate further back into the 
primary mouth-cavity, so that they are surrounded by hard bony portions of 
the jaw (as is yet permanently the case in the higher Amphibia). 

Fifth Stage : Nose of the Frotamnia. 

The primitive mouth-cavity, into which both nasal canals open, separates, 
in consequence of the fonnation of a horizontal partition (the palate-roof), 
into an upper nasal cavity and a lower (secondary) mouth-cavity. The 
formation of the spongy bones of the nose commences (as in the earlier 
Amnion Animals). 

Sixth Stage : Nose of the earlier Mammal». 

The simple nose-cavity separates, in consequence of the development of 
a vertical partition wall (the "plough," vomer), into two distinct noSe-cavities, 
each of which is occupied by one of the nasal canals (as is yet the case in all 
Mammals). The spongy nose-bones differentiate. 

Seventh Stage : Nose of the more recent Mamtnals. 

Within both nose-cavities the development of the spongy bones proceeds 
further, and an external nose begins to form. 

Eighth Stage : Nose of the Catarhine Apes, 

The internal and the external nose attain the full development e»» 
oiusively oharacteiistic of Catarhine ADes and of Man. 



250 



THE EVOLUTION OF MAN. 



The history of the development of the eye is equally 
remarkable and instructive. For although the eye, owing 
to its exquisite optical arrangement and wonderful struc- 
ture, is one of the most complex and most nicely adapted 
organs, yet it develops, without a preconceived design, from 
a very simple rudiment in the outer skin-covering. 




t 



Fig. 241. — The human eye in transverse section: a, protective membrane 
(sclerotica); &, horn membrane {cin-nea); c, outer membrane (conjunctiva); 
d, circular veins of iris ; e, vascular membrane (clioroidea) ; /, ciliary 
muscle ; g, corona ciliaris ; h, rainbow membrane {iris) ; i, optic nerve 
{n. opticus) ; k, anterior limit of the retina ; I, crystalline lens {lens crystal- 
Una)', m, inner cover of the horn membrane (water membrane, membrana 
Descemeti); n, pigment membrane {pigmentosa); o, retina; p, ^'petits-csinal;" 
q, yellow spot of the retina. (After Helmholtz.) 

When fully developed, the human eye is a globular 
capsule (the eyeball, hidbus, Fig. 241). This lies in the 



THE EYE. 251 

bodxj orbit of th« skuU, surrounded by protective fat and 
by motor muscles. The greater part of this eyeball is 
occupied by a semi-fluid, clear gelatinous substance, the 
vitreous body (corpus vitreum). The crystalline lens 
(Fig. 241, l) is embedded in the anterior surface of the 
vitreous body. It is a lentil-shaped, bi-convex, transparent 
body — the most important of the light-refracting media of 
the eye. Among these media is, in addition to the lens 
and vitreous body, the aqueous humour (humor aqueus, at 
m, in Fig. 241), in front of the lens. These three peUucid, 
light-refracting media — the vitreous body, the crystalline 
lens, and the aqueous humour — ^by which the rays of light, 
incident on the eye, are refracted and concentrated, are 
enclosed in a firm globular capsule consisting of several 
different membranes, comparable with the concentric layers 
of an onion. The outer and thickest of these forms the 
white protective membrane of the eye {sclerotica, a). It 
consists of firm, compact white connective tissue. In front 
of the lens a circular, very convex, transparent plate, re- 
sembling a watch glass, is inserted in the white protective 
membrane; this is the horny membrane (corTiea, h). On 
its outer surface the homy membrane is covered by a very 
thin coating of outer skin (epidermis) ; this coating is 
called the connecting membrane (conjunctiva); it extends 
from the homy membrane over the inner surface of both 
eyelids — the upper and lower folds of skin which on closing 
the eyes are drawn together over them. At the inner 
comer of our eye there is, as a sort of rudimentary organ, 
the remnant of a third (inner) eyelid, which, as the " nic- 
titating membrane," is highly developed in the lower 
Vertebrates (vol. i. p. 110). Below the upper eyelid are lodged 



252 THE EVOLUTION OF MAN. 

the tear-glands, the secretion of which keeps the surface 
of the eye smooth and clean. 

Directly under the protective membrane is a delicate 
darkrred, highly vascular membrane, the vascular mem- 
brane (choroidea, e), and within this the retina (0), which 
is a dilatation of the optic nerve (i). This latter is the 
second brain nerve. It extends from the " centre of sight " 
(the second brain-bladder) to the eye, penetrates the outer 
coats of this, and then extends, as the retina, between the 
vascular membrane (choroidea) and the vitreous body 
(corpus vitreum). Between the retina and the vascular 
membrane lies another very delicate membrane, which 
is commonly, but wrongly, considered as part of the latter. 
This is the black pigment membrane (pigmentosa, lamina 
pigTuenti, n), or the " black carpet " (tapetum nigrum). 
It consists of a single layer of beautiful hexagonal cells 
accurately joined together and filled with black pigment 
gi'anules. This pigment membrane lines, not only the inner 
surface of the actual vascular membrane, but also the pos- 
terior surface of its anterior muscular prolongation, which, 
as a circular ring-like membrane, covers the edge of the lens, 
and prevents the penetration of lateral rays. This is the 
well-known "rainbow membrane" (iris, /i), which is differently 
coloured in different persons (blue, gray, brown, etc.). This 
" rainbow membrane " is the limit towards the front of 
the vascular membrane. The round hole in the iris is the 
pupU, through which the rays of light pass into the interior 
of the eye. Where the iris proceeds from the edge of the 
actual vascular membrane, the latter is much thickened and 
forms a beautiful ciliated crown (corona ciliaris, g), which 
surrounds the edge of the lens with about seventy large, 
afid mamj smaller rays. 



DEVELOPMENT OF THE EYE. 253 

In the embryo of jMan, as in that of all other Amphi- 
rhina, two pear-shaped vesicles grow out laterally, at a very 
early period, from the foremost part of the first brain - 
bladder (Fig. 223, a, p. 218). These bladder-like protuberances 
are the primary eye-vesicles. At first they are directed 
outward and forward, but they soon make their way further 
downward, so that after the specialization of the five brain- 
bladders, they lie at the base of the twixt-brain. The 
internal spaces within the two pear-shaped vesicles, which 
soon attain a considerable size, communicate through their 
hollow stalks with the cavity of the twixt-brain. Their 
outer covering is formed by the outer skin-covering (horn- 
plate and leather-plate). Where, on each side, the latter 
comes directly in contact with the most curved portion of 
the primary eye-vesicles, a thickening {I) arises, and at the 
same time a groove-like indentation (0) in the horn-plate 
(Fig. 242, 1). This groove, which we will call the lens groove, 
changes into a closed sac, the thick- walled lens vesicle (2, Q, 
owing to the fact that the. edges of the groove coalesce above 






y 



a- 

I- 



i 

IS 






w 



\ 




IV 



Fig. 242.— Eye of an embryonic Chick in longitudinal section (1, of a 
germ after sixty-five hours of incubation ; 2, of a somewhat older germ ; 
3, of a germ four days old) : ?i, hom-plate ; 0, lens groove ; Z, lens (in 1, 
it still forms part of the epidermis, while in 2 and 3 it has separated); », 
thickening of the hom-plate at the point from which the lens separated j 
;Z, vitreous body ; r, retina; u, pigment membrane. (After Remak.) 



2 54 THE EVOLUTION OF MAJI. 

it. Exactly as the medullary tube originally separates from 
the outer germ-layer does this lens-sac separate from the 
horn-plate, in which it originated. The space within this 
sac is afterwards entirely filled by the cells of its thick wall, 
and the solid crystalline lens is thus formed. The latter is, 
therefore, purely a formation of the epidermis. Together with 
the lens the small fragment of the leather-plate (corivm) 
lying below the lens separates from the outer skin-covering. 
This siiiall piece of the leather-skin very soon forms a highly 
vascular sac round the lens (capsula vasculosa lentis). 
Its anterior portion at first covers the pupillary orifice, and 
is then known as the pupillary membrane (membrana 
pupillaris). Its back portion of the same membrane is called 
the " memhrana capsulo-pupillaris." This "vascular lens 
capsule, which merely serves to nourish the growing lens," 
afterwards entirely disappears. The later, permanent lens 
capsule contains no vessels, and is a structureless secretion 
of the lens cells. 

As the lens thus separates from the horn-plate and 
grows inward, it must necessarily indent the adjoining 
primary eye-vesicles from without (Fig. 242, 1-3). This 
process may be compared to the inversion of the germ-mem- 
brane vesicle (hlastula), which in the Amphioxus and in 
many low animals gives rise to the gastrula (voL i. p. 192). In 
both instances the inversion of one side of the closed vesicle 
proceeds until finally the inner, inverted portion touches the 
outer, uninverted portion of the wall of the vesicle, so that 
the cavity disappears. Just as in the gastrula the former 
part changes into the intestinal layer (eTitoderTna), and 
the latter into the skin-layer (exoderTna), so in the inverted 
primary eye-vesicle the retina develops from the former 



DEVELOPMENT OF THE EYE. 255 

(inner) part (Fig. 242, r), and the black pigment membrane 
(w) from the latter (the outer, uninverted part). The hollow 
stalk of the primary eye-vesicle changes into the optic 
nerve. 

The lens (I) which enacts so important a part in this 
inverting process of the primary eye-vesicle, lies at first 
directly upon its inverted part, that is, on the retina (r). 
Very soon, however, the two separate, a new body, the 
vitreous body {corpus vitreum, gl), coming in between them. 
While the lens-sac is detaching itself, and the primary eye- 
vesicle is being inverted from without, another inversion 
simultaneously proceeds from beneath — from the superficial 
portion of the skin-fibrous layer, i.e., from the leather-plate 
of the head. At the back of the lens and below it, a ledge-like 
process of the leather-plate arises (Fig. 243, g), which inverts 
the primary eye-vesicle (now shaped like a cup) from below, 
and presses in between the lens (I) and the retina (r) 
Thus the primary eye-vesicle assumes the form of a hood. 
The opening of this hood, answering to the face, is covered 
by the lens ; but the opening, through which the neck 
would pass, answers to the indentation through which the 
leather-skin passes in between the lens and the retina (the 
inner wall of the hood). The space within this secondary 
eye-vesicle is almost filled by the vitreous body, which 
answers to the head wrapped in this hood. The liood itself 
is, properly speaking, double : the inner hood itself is the 
retina, and the outer one, directly surrounding the former, 
is the pigment membrane. The comparison with a hood 
renders this process of inversion, which is sometimes hard 
to explain, more clearly understood. The rudiment of the 
vitreous body {corpus vitreum) is at first very incon- 
50 



256 



THE EVOLUTION OF MAN. 



siderable (Fig. 243, g), and the retina disproportionally 
thick. As the former expands, the latter becomes much 
thinner, till at last the retina appears only as a very delicate 



Fig. 243, — Horizontal traijaverBe 
Bection through the eye of a human 
embryo of four weeks ; 100 times 
enlarged (after Koelliker) : i, lens 
(the dark wall of which is equal to 
the diameter of the central cavity) ; 
g, vitreous body (connected with the 
leather-plate by a stalk, g') ; v, vas- 
cular loop (penetrating through the 
stalk {g') into the vitreous body be- 
hind the lens) ; r, retina (inner, 
thicker, inverted lamella of the 
primary eye-vesicle) ; a, pigment membrane (outer, tfiinner, uninverted 
lamella of the same) ; K, intermediate space between the retina and the 
pigment membrane (remnant of the cavity of the primary eye-vesicle). 




coat of the thick, almost globular vitreous body, which fills 
the greater part of the secondary eye-vesicle. The outer 
layer of the vitreous body changes into a highly vascular 
capsule, the vessels of which afterwards disappear. 

The slit-like passage through which the rudiment of the 
vitreous body grows from below in between the lens and 
the retina, of course causes a break in the retina and the 
pigment-membrane. This break, which appears on the inner 
surface of the vascular membrane as a colourless streak, has 
been inaptly called the choroidal cleft, though the true 
vascular membrane is not cleft at all at this point (Fig. 
234, s'p, 235, sp, p. 243). A thin process of the vitreous body 
passes inward on the under surfiice of the optic nerve, which 
it inverts in the same way as tlie primary eye-vesicle was 
inverted. The hollow cylindi-ical optic nerve (tlie stalk of 



DEVELOPMENT OF THE EYE, 257 

the primary eye-vesicle) is thus transformed into a channel^ 
opening downward. The inverted lower surface attaches 
itself to the uninverted upper surface of the hollow stalk, so 
that the hollow space within the stalk, forming the com- 
n^unication between the cavity of the twixt-brain and of 
the primary eye-vesicle, now disappears. The two edges 
of the channel now grow downward toward each other, 
enclose the band-like process of the leather-plate, and 
coalesce beneath it. Thus this process now lies within the 
axis of the solid secondary optic nerve. It develops into 
a cord of connective tissue carrying the central blood-vessel 
of the retina {vasa centralia retince). 

An entirely fibrous covering, the fibrous capsule of the 
eye, now finally forms round the outside of the secondary 
eye-vesicle and its stalk (the secondary optic nerve). It 
originates from the head-plate, from that part of the skin- 
fibrous layer which immediately encloses the eye-vesicle. 
This fibrous covering takes the form of a completely-closed 
globular sac, which surrounds the whole ball of the eye, and 
on the outer side of this, grows in between the lens and the 
hom-plate. The globular waU of the capsule soon separates, 
by fission of the surface, into two distinct membranes. The 
inner membrane becomes the choroidea, or vascular layer; 
in front it forms the ciliated crown (corona ciliaris) and 
the iris. The outer membrane, on the other hand, becomes 
the white enveloping, or protective membrane {sclerotica)^ 
and, in front, forms the transparent homy membrane 
(cornea). The rudiments of all the essential parts of the 
eye are now formed, and its farther development is only in 
details, in the complex differentiation and combination of 
the several parts. 



( 258 ) 



TABLE XXXI. 

B/rtemstic Surrey of the Development of the Human Eye. 



L Qjstcinatlo Surrey of those parts of the Hnman Eye which develop from the first of tkn 
Secondary Germ-layers, the Skin-sensory Layer. 



A. 
Products of the 

Marrow-plat« 



B. 

ProdnctB of the 

Horn-plate 



^1. stem of the primary 
eye-vesicle 

Inner (inverted) part of 
the primary eye- 
vesicle 

Outer (uuinverted) part 
of the primary eye- 
vesicle 

Vesicle separated from 
the horny plate 

6. Outer epidermic skin 

6. Inverted portions of the 
epidermic sldn 



1. Optic nerve 
a. Betliu 



3. Screen, or pig- 
ment-coat 



4. Crystalline lens 

6. Connective mem- 
brane 

6. Te&r-glands 



Iftrvut optieu* 
Bttina 



Pigmentosa (tamina 
pigmentiy 



Lens cryiidllina 
Conjunctiva 
Cflandulaa lacrymalet 



11. Systemailo Survey of those parts of the Human Eye which develop from the second of th< 

Secondary Germ-layers, the Skin-fibrous Layer. 



'"7, 8. Ledge-like process of 7. Vitreous body Corpus vitreum 

the corium on the 8. Vascular mem- Capsula vasculosa 

lower side of the pri- brane of the corporis vitrei 
mary eye-vesicle vitreous body 



Prod«eU«f the 
LeathMT-plate 



Products of the 

sioOHplftt* 



9. Central vessels of 
the retina 



VasaceniraUa 
retince 



9. Continuation of the 
corium process 

10. Pupillary membrane, 10. Vascular mem- Capsula vatculotek 
with its capsule brane of the lentis cryst4MinA 

lens 



11. Folds of the leather 11. Eyelids 
^ skin (corium) 



Palpti)f\m 



flit 13. Vascular mem- 
brane of the eye- 
ball (capsula vas- 
culosa bulbij) 

14, 16. Fibrous membrane 
of the eyeball (cap- 
tviajibrosa bulbi) 



mem- Cfktroide^ 
mem- M$ 



12. Vascular 

brane 

13. Rainbow 

brane 

14. Protective mem- Sclerotiea 

brane 
18. Homymembraos Oomea 



THE NICTirATING MEMBRANE. 259 

The most important fact in this remarkable process of 
eye-development is the circumstance that the optic nerve, 
the retina, and the pigment-membrane originate from a 
part of the brain, from a protuberance of the twixt-brain, 
while the crystalline lens, the most important refracting 
medium, develops from the outer skin (epiderTnis). From 
the outer skin — the homy lamina — originates also the 
delicate connecting membrane (conjunctiva) which after- 
wards envelopes the outer surface of the eyeball. The tear- 
glands proceed, as branched processes, from the conjunctiva 
(Fig. 214, p. 202). All the other parts of the eye originate 
from the skin-fibrous layer; the vitreous body and the 
vascular lens-capsule from the leather-plate, the choroid 
coat with the iris, and the protective membrane (sclerotica) 
with the homy membrane (cornea) from the head-plates. 

The outer protective organs for the eye, the eyelids, are 
merely simple folds of skin, which, in the human embryo, 
appear in the third month. In the fourth month the upper 
eyelid adheres to the lower, and the eye then remains 
covered by them till birth. (Plate VII. Fig. M ill., R iii., 
etc.) The two eyelids usually again separate shortly before 
birth, but sometimes not till after. Our skuUed ancestors 
had, in addition to these, a third eyelid, the nictitating 
membrane, which was drawn over the eye from the inner 
comer. Many Primitive Fishes (SelacJiii) and Amnion 
Animals yet retain this. In Apes and in Man it has atrophied, 
and only a small remnant of it exists in the inner comer of 
the eye as the " crescent-shaped fold," as a useless " rudi- 
mentary organ." (Cf vol. i. p. 109.) Apes and Man have 
also lost the " Harder gland," opening below the nictitating 
membrane, which appears in other Mammals, and in Birds, 
Reptiles, and Amphibians. 



26o 



THB EVOLUTION OF MAN. 



The ear of Vertebrates develops in many important 
points similarly to the eye and nose, but yet in other 
lespects very differently.^*'^ The organ of hearing of the 
developed human being resembles that of other Mammals 
in all essential particulars, and is especially similar to that of 
Apes. As in the laiter, it consists of two principal parts, an 
apparatus for the conveyance of sound (external and middle 
ear) and an apparatus for producing the sensation of sound 
(internaJ ear). The outer ear opens in the ear-shell (concha 




Fie. S44. — Anditory organ of man (left ear, seen from the front; natnra] 
aiae) : a, ear-shell : h, external ear-caual ; c, drum, or tympanic membrane j 
d, cavity of drum ; e, ear-trumpet; /, g, 7i, the three ear honelets (/, hammer ; 
g, anvil ; h, stirnip) ; i, ear-pouch (utriculus) ; k, the three semi-circula* 
canals ; I, ear-sac (sacculus) ; m, snail (cochlea) ; n, auditory nerve. 

auris), situated at the side of the head (Fig. 224, a). From 
this the outer ear-canal, which is usually about an inch long^ 
leads to the inside of the head (h). The inner end of this 



THE EAU. 261 

tube is closed by the well-known tympanic membrane 
or drum {tympanum) ; a thin membrane of oval form (c), 
placed in a vertical position, but slightly inclined. This 
membrane separates the outer ear-canal from the so-called 
cavity of the drum (cavum. tympani). This is a small 
cavity enclosed in the petrous part of the temporal bone, 
which is filled with air and connected by a special tube with 
the moutli-cavity. This tube is somewhat longer, but much 
narrower than the outer ear-canal ; it leads inward and 
forward in an oblique direction from the inside wall of the 
tympanum and opens behind the inner nostrils (or Choana) 
into the upper part of the cavity of the throat (pharynx). 
This canal is called the Eustachian tube (tuha Eustachii). 
It equalizes the pressure of the air in the tympanic 
cavity, and the outer atmospheric air which enters by 
the ear canal. Both the Eustachian tube and the tympanic 
cavity are lined by a thin, mucous membrane, which 
is a direct continuation of the mucous membrane of the 
throat. Within the tympanic cavity are the three bonelets 
of the ear, which, from their characteristic shape, are called 
the hammer, the anvil, and the stirrup (Fig. 244 /, g, h). 
The hammer (/) lies furthest outward, just within the 
tympanic membrane; the anvil (g) is wedged in between 
the two others, above the hammer, and further in than the 
hammer ; and, lastly, the stirrup (h) lies next to the anvil 
toward the inside, and touches with its base the outer waD 
of the internal ear, or the auditory sac. All these parts of 
the middle and external ear belong to the sound-conducting 
apparatus. Their principal office is to convey the waves ol 
sound from without throu!ih the thick side-wall of the head, 
to the internal ear. In Fishes these parts are entirely unre- 



262 THE EVOLUTION OF MAN. 

presented. In them, the sound-waves are conveyed directly 
through the wall of the head itself to the internal ear. 

The inner apparatus, that which produces the sensation 
of sound, receiving the sound-waves thus conveyed to it, 
consists in Man, as in all other Vertebrates (with the single 
exception of the Amphioxus), of a closed auditory sac filled 
with fluid, and of an auditory nerve, the ends of which are 
distributed over the wall of this sac. The vibrations of 
the waves of sound are conveyed by that medium to these 
nerve-ends. In the auditory fluid (endolymph), which 
fills the labyrinth, and opposite the places at which the 
auditory nerves enter, are some smaU stones, composed 
of a mass of microscopic calcareous crystals (otoliths). The 
organs of hearing of most Invertebrates have essentially 
the bame construction. In them, also, it usually consists of 
a closed sac filled with fluid, containing otoliths, and having 
the auditory nerve distributed over its wall. But while in 
Invertebrates the auditory vesicle is usually of a very 
simple spherical or oval form, in all Amphirhina, on the 
contrary, that is, in all Vertebrates above the Fishes up to 
Man, it is distinguished by a very characteristic and singular 
form known as the auditory labyrinth. This thin membra- 
nous labyrinth is enclosed in a bony envelope of the same 
form, the osseous labyrinth (Fig. 245), which lies within the 
petrous bone of the skull. The labyrinth in aU Amphirhina 
is divided into two sacs. The larger sac is called the 
auditory pouch (utriculus), and has three curved appendages, 
called the semi-circular canals (c, d, e) ; the smaller sac is 
called the auditory sac (saccuhts), and is connected with a 
peculiar appendage, which in Man and the higher Mammals 
is distinguiBhed by a spiral form, like the shell of a snails and 




DEVELOPMENT OF THE EAB. 263 

henoe is called the " snail " {cochlea, h). On the thin wall 
of this delicate membranous labyrinth, the auditory nerve, 
which passes from the after-brain to the labyrinth, is dis- 
tributed in a very complex manner. It divides into two 
main branches, the nerve of the cochlea, and the nerve of 
vestibule, for the remaining part of the labyrinth. The 
former seems specially to determine the quality of the sound 
heard, the latter its quantity. The nerve of the cochlea 

Fio. 245. — The bony labyrinth of the human ear 
(left side) : o, vestibnle ; h, cochlea ; c, upper semi- 
circular canal; d, posterior semi-circular canal; «, 
outer semi-circular canal ; f, fenestra ovalis ; g, fenestra 
rotwnda. (From Meyer.) 

tells US the pitch and quality of sounds, the nerve of the 
vestibule their strength. 

The first rudiment of this extremely complex organ of 
lu^aring is very simple in the human embryo, as in those 
uf all other Skulled Animals (Craniota) ; it is a groove-like 
depression of the outer skin (epidermis). At the back of the 
head, near the after-brain, at the upper end of the second 
gilJ -opening, a little wart-like thickening of the horn-plate 
arises on each side (Figs. 24;6, A,fl; 248, g). This deepens 
into a small groove, and separates from the outer-skin, just 
as does the lens of the eye. (Cf. p. 253.) A small vesicle 
filled with fluid, the primitive ear-vesicle, is thus formed 
on each side, immediately below the horn-plate of the back 
part of the head ; this is also called the " primary laby- 
rinth " (Plates VI. and VII.). As this separates from ita 
original site, the horn-plate, and grows inward and down- 
ward in the skull, it changes from a globular to a pear- 
shaped form (Figs. 246, B, Iv ; 249, 0). The outer part has 



264 THE EVOLUTION OF MAN. 

elongated into a thin stalk, which at first opens outward in 
a narroAv canal. (Cf. Fig. 137,/, vol. i. p. 382.) This is called 
the appendage of the labyrinth recessus labyrinthi,Fig. 246, Ir). 






Fig. 246. — Development of the ear-labyrinth of a Chick, in five con- 
secutive stages (A-E) (cross-sections through the rudimentary skull) : fl, 
ear-groove ; Iv, ear-vesicle ; Ir, labyrinth appendage ; r., rudiment of the 
cochlea; csp, hind semi-circular canal; cse, outer semi-circular canal; 
jr, jugular vein. (After Eeissner.) 

Figs. 247, 248. — Head of an embryonic Chick, on the third day of incuba- 
tion : 247 in front, 248 from the right ; n, rudimentary nose (olfactory 
groove) ; I, rudimentary eye (ocular groove) ; g, rudimentary ear (auditory 
groove) ; V, fore-brain ; gl, eye-slit ; o, process of the upper jaw ; u, process 
of the lower jaw of the first gill-arch. (After Koelliker.) 

Fig. 249. — Primitive brain of human embryo of four weeks, in vertical 
section, and the left half observed from within : v, z, m, h, n, the five grooves of 
the skull cavity in which the five brain bladders are situated (fore, twixt, 
mid, hind, and after brains) ; o, primary, pear-shaped auditory vesicle 
(showing through) ; a, eye (showing through) ; Tio, optic nerve ; p, canal of 
the hypophysis ; t, central skull-pieces. (From Koelliker,) 



DEVELOPMENT OF THE EAR. ' 265 

In lower Vertebrates, this develops into a peculiar cavity 
filled with calcareous crystals, which in some Primitive 
Fishes (Selachii) remains permanently open, and open^ 
above on the skull (ductus endolymphaticus). In Mam-* 
mala, on the contrary, the appendage of the labyrinth 
atrophies. In these, it is of interest only as a rudimentary 
organ, which has no longer any physiological significance. 
Its useless remnant traverses the osseous wall of the petrous 
bone in the form of a narrow canal, and is called the aque- 
duct of the vestibule {aquceductus vestihuli). 

Only the inner and lower part (extended like a bladder) 
of the detached ear-vesicle develops into the differentiated 
and extremely complex structure which is afterwards known 
as the " secondary labyrinth." This vesicle separates at a 
very early stage into an upper, larger section, and a lower, 
smaller section. The former gives rise to the ear-pouch 
(utriculus) with the three semi-circular canals; from the 
latter proceeds the ear-sac (sacculus) with the "snail" 
(cochlea, Fig. 246, c). The three semi-circular canals 
originate as simple pocket-like processes from the ear- 
pouch (Fig. 246, E, cse and csp). In the centre of each of 
these processes, the two walls coalesce, and separate them- 
selves from the utricle, while their extremities still commn 
nicate with its cavity. In all Double-nostrils (Amjpliirhina) 
there are three semi-circular canals, as in Man, while of the 
Cyclostomi the Lampreys have but two, and the Myxinoides 
but one (p. 103). The highly-developed structure of the 
" snail " (cochlea), which is one of the most delicate and 
admirable products of adaptation in the mammalian body, 
originally develops very simply as a bottle-like process 
from the ear-sac (sacculus). As Hasse has shown, the 



266 THE EVOLUTION OF MAN. 

various stages in its ontogenetic development still exist 
permanently side by side in the ranks of the lower Vert.e- 
brates.^'^ Even in Monotremes the snail-like spiral curving 
of the cochlea is not present ; it is exclusively characteristic 
of the other Mammals and Man. 

The auditory nerve (nervus acusticus), or the eighth 
brain-nerve, — one of the main branches of which distributes 
itself over the " snail " (cochlea), the other over the other 
parts of the labyrinth, — is, as Gegenbaur has shown, the 
sensory* dorsal branch of a spinal brain-nerve, the motor 
ventral branch of which is the motor nerve of the facia] 
muscles {nervus facialis). Phylogenetically it has, there- 
fore, originated from an ordinary skin-nerve, and is, conse- 
quently, of wholly different origin from the optic and 
olfactory nerves, which represent the two direct processes 
of the brain. In this respect the organ of hearing differs 
essentially from the organs of sight and of smell. The 
auditory nerve originates from the cells of the head-plate ; 
therefore, from the skin-fibrous layer. From this also 
develop all the membranous, cartilaginous, and bony cover- 
ings of the ear-labyrinth. 

The development of the apparatus for the conveyance of 
sound, situated in the middle and external ear of Mammals, 
is entirely distinct from that of the apparatus of auditory 
sensation. It must be regarded, phylogenetically as well as 
ontogenetically, as an independent, secotidary formation, 
which only afterwards connects itself with tlie primary 
internal ear. Its development is, however, not less in- 
teresting, and is equally clearly explained by Comparative 
Anatomy. In all Fishes, and in the yet lower Vertebrates, 
there is no special apparatus for the conveyance of sound. 



( 267 ) 
TABLE XXXII. 

SnmCATIG SURYEY OF THE GhIEF StAOES IN THK DbVSLOPMSIIT 

OF THE Human Ear. 

I. First Stage. 

The auditory nerre is an ordinary sensitive skin-nerve, which, daring the 

differentiation of the horn-plate, appears at a certain point on the skin of 

the head. 

n. Second Stage. 

The differentiated place of the horn. plate, at which the auditory nerve 

appeared, forms a small special auditory groove in the skin, which has an 
outer orifice in the appendage called the " labyrinth." 

III. Third Stage. 
The auditory groove has detached itself from the horn-lamina, and forms 
a small closed auditory vesicle filled with fluid. The ' labyrinth-appendage" 
becomM mdimentaiy {Aquaductv^ vestihuli) . 

rV. Fov/rth Stage. 
The auditory vesicle differentiates into two connected parts, the ear- 
pouch (utricuhia) and the ear.sac (^sacculus). Each of the two vesicles 
receives a special main branch of the auditory nerve. 

V. Fifth Stage. 

Three semi-oironlar canals grow from the ear -pouch (as in all Amphi- 

rhind), 

VL Sixth Stage. 

The ** snail '* (cochlea) grows from the ear-sac in Fishes and Amphibia ; 
it is very insignificant, and is only developed as an independent part in the 

Amniota. 

VII. Seventh Stage. 

The first gill-opening (the blow-hole of Selachians) changes into the 
tympanic cavity and the Eustachian tube ; the former is externally closed 
by the tympanic membrane (Amphibia). 

VIII. Eighth Stage. 

The small bones of the ear (ossicula cuuditus) (the hammer (malleiU) and 
anvil (incus) from the first gill-arch, the stirrup (atapes) &om the second) 
develop from parts of the first and second gill-arches. 

IX. Ninth Stage. 
The external ear is developed, together with the bony ear-canal. The 
shell of the ear is pointed and movable (as in most lower Mammals). 

X. Tenth Stage. 
The ear-shell, with its muscles, becomes disused and a rudimentary 
organ. It is no longer pointed, but, on the contrary, has a onrved rim wMh 
a small ear-flap (as in Anthropoid Apes and Men). 



( 2^^ ) 



TABLE XXXIII. 

SjEitematio Survey of the Development of the Hainan Ear. 



I. Surrey of the parts of the Internal Ear. (Apparatus perceptlre of souaA.) 



1. Stalk of the primary 1. 4<luP<^uct of the Aqu(Eductu$ vesttbuli 

ear- vesicle vestibule (Due- s.Recettutldhyrintki 

tus endolym- 
phaticiis) 

riiLjii-f^jif thf J 2, 3. Upper part of the 2. Ear-pouch Utriculut 

mancis oi me < primary ear-vesicle 3. Three seml-circu- Canale* ttmi-cireu- 



Eonx-plate 



lar, or curved 
canals 



4, 5. Lower part of the 4. Ear-sac 

primary ear- vesicle 5. "The snail" 



lart* 

Sacculut 
Cochlea 



B. 

Products of the 

Head-plate 



6. Auditory nerve 6. Auditory nerve Ntrvus aeuttiau 

1. Bony covering of the 7. Osseous labyrinth Labyrinthiu otaexu 
membranous laby- 
rinth 

8. Bony covering of the 8. " The stony bone " 0$ petrotum 

\ whole internal ear 



n. Survey of the parts of the Intermediate and External Ear. (Apparatus for the 

conveyance of sound.) 



C 
Products of the 

first 

OiU-opeuing 



/- 9. Inner part of the first 

gill-opening 

10. Central p irt of the first 

gill-opening 



11. Closed part of the first 
gill-opening 



/12. Upper part of the 
second gill-arch 



D. 

Products of the 
first two 

Gill-arohei 



Prodack of the 

Head-plate 



Product of the 
Skm-oov«ring 



< 



13. Upper part of the first 

gill-arch 

14. Central part of the first 

gill-arch 



16. Tympanic circle 

(Annulus tympanicut) 

'16. Circular membranous 
fold at the closed part 
of the first gill- 
oponing 



9. Eustachian tube Thiba Eustachii 

10. Tympanic cavity Cavwm tympani 

(Interior of the 
drum) 

11. Tympanic mem- Mcmbrana tympani 

brane (Head of 
the drum) 

12. Stirrup (First Sta/pt» 

bonelet of the 
ear) 

13. Anvil (Second IneuB 

bonelet of the 
ear) 

14. Hammer (Third MaOeuM 

bonelet of the 
ear) 

15. Bony outer audi- Maahu oudUorim 

tory passage otteut 



16. Ear-shell 



Oonchaauria 



17. Rudimentary ear- Muaouli oonchat 



DEVELOPMENT OF THE EAR. 269 

no external and middle ear ; in these animals there is only 
a labyrinth, an internal ear, situated within the skull. The 
tympanic membrane, its cavity, and all the connected parts 
are unrepresented. The middle ear first develops in the 
Amphibian class, in which a tympanic membrane, a tym- 
panic cavity, and an Eustachian tube are first found All 
these essential parts of the middle ear develop from the first 
gill-opening, with its surrounding parts, which in the Pri- 
mitive Fishes {Selachii) remains through life as an open 
blow-hole, situated between the first and second gill-arches. 
In the embryos of higher Vertebrates it closes in the centre, 
the point of concrescence forming the tympanic membrane. 
The remaining outer part of the first gill-opening is the 
rudiment of the outer ear-canal. From the inner part 
originates the tympanic cavity, and further inward, the 
Eustachian tube. In connection with these, the three bone- 
lets of the ear develop from the first two gill-arches; the 
hammer and anvil from the first, and the stirrup from 
the upper end of the second gill-arch.^''* 

Finally, as regards the external ear, the ear-shell {concha 
auris), and the outer ear-canal, leading from the shell to the 
tympanic membrane — these parts develop in the simplest 
way from the skin -covering which borders the outer orifice 
of the first giU-opening. At this point the ear-shell rises in 
the form of a circular fold of skin, in which cartilage and 
muscles afterwards form (Fig. 238, p. 247). This organ is 
also limited to Mammals. Among them, it is originally 
wanting only in the lowest division, in the Beaked Animals, 
(Monotrema). In the others, on the contrary, it appears 
in very difierent stages of development and partly also of 
atrophy. The ear-shell has atrophied in most a(^uatic 



270 



THE EVOLUTION OF MAN. 



Mammals. Most of these have even lost it entirely ; this 
is so, for example, in the Sea-cows and Whales, and most 
Seals. On the other hand, in the great majority of Pouched 
Animals (Marsupialia) and Placental Animals (Placentalia), 
the ear-shell is well developed, receives and concentrates the 
waves of sound, and is provided with a highly-developed 
muscular apparatus, by means of which it can be turned 
freely to all sides, and at the same time can be changed in 
form„ Every one must have noticed how strongly and freely 
our domestic Mammals, Horses, Cows, Dogs, Rabbits, etc., 
can " prick " their ears, erect them and turn them in different 
directions. Most Apes yet retain the power of doing this, 
and our ancient Ape progenitors could also do it. The more 




Fig. 250. — Rudimentary ear.muscles on the human skull : a, upward 
muscle {m. attollens) ; l, forward muscle (m. attrahens) ; c, backward muscle 
(m. retrahens) ; d, larger muscle of the helix (m. helicis major) ; e, smaller 
muscle of the helix (m. helicis minor); f, muscle of the tragus (m. tragicus); 
(/ muscle of the antitragus (m. antitragicus) . (After H. Meyer.) 

recent Ape ancestors, common to Men and to the Anthropoid 
Apes (Gorilla, Chimpanzee, etc.), discontinued the habit of 
moving their ears, and hence the motor muscles gi'adually 



THE EAR IN MAN AND APES. 271 

became rudimentary and useless. We still, however, possess 
them (Fig. 250). A few individual men can even move their 
ears forward or backward a little by the use of the forward 
muscle (b) and the backward muscle (c) ; and by long 
practice these motions can be gi'adually increased. On the 
other hand, no man is able to erect the ear-sheU by the 
upward muscle (a), or to change its form by the little inner 
muscles of the ear (d, 6, /, g). These muscles, which were 
very useful to our ancestors, have become entirely un- 
important to us. This is equally true of Anthropoid Apes. 

We also share only with the higher Anthropoid Apes — 
the Gorilla, Chimpanzee, and Orang — the characteristic form 
of our human ear-shell, especially the rolled edge, the helix, 
and the ear-flap. The lower Apes, like all other Mammals, 
have pointed ears without the helix, and without ear-flaps. 
Darwin has, however, shown that in some men a short, 
pointed process, not occurring in most individuals, is per- 
ceptible at the upper part of the folded rim of the ear. In 
some few individuals, this process is very well developed. 
It can only be explained as the remnant of the original 
point of the ear which, in consequence of the folding of the 
edge of the ear, has been bent forward and inward. 
(Cf. the similarly folded ear in the embryo of the Pig 
and Cow, Plate VII. Fig. H iii. and G in.) On carefully 
comparing the ear-sheUs of Man and of the various Apes in 
this particular, we find that they form a connected series of 
retrograde steps. In the common catarhine ancestors of the 
Anthropoids and of Man, this retrogression began with the 
folding down of the ear-shell. In consequence of this, the 
ear-edge was formed on which that significant comer 

appears, the last trace of the free prominent point of the ear 
51 



2/- THE EVOLUTION OF MAN. 

a our older Ape ancestors. Thus it is possible even here, 
vsrith the help of Comparative Anatomy, to trace this human 
organ from the similar but more highly-developed organ of 
the lower Mammals, with certainty. At the same time. Com- 
parative Physiology shows us that this organ is of more 
or less high physiological value to the latter, while in 
Anthropoids and Man it is a useless rudimentary organ. 
Men with their ears cut off can hear as well as they did 
before* The conveyance of sound is not affected by the loss 
of the ear-shell. This explains the great diversity in the 
form and size of the ear-shell in different persons ; it shares 
this high degree of variability with other rudimentary 
orgaiis.iT^ 



CHAPTER XXII. 
DEVELOPMENT OF THE ORGANS OF MOTION. 

The Motire Apparatus of Vertebrates. — These jure constitnted by the 
Passive and Active Organs of Motion (Skeleton and Muscles). — The 
Significance of the Internal Skeleton of Vertebrates. — Structure of the 
Vertebral Column. — Formation and Number of the Vertebrae. — The Ribs 
and Breast-bone. — Germ-histoiy of the Vertebral Column. — The Noto- 
chord. — The Primitive Vertebral Plates. — The Foniiation of the Meta- 
mera. — Cartilaginous and Bony Vertebrae. — Intervertebral Discs. — 
Head-skeleton (Skull and Gill-arches). — Vertebral Theory of the Skull 
(Goethe and Oken, Huxley and Gegenbaur). — Primitive Skull, or 
Primordial Cranium. — Its Formation from Nine or Ten Cofilescent 
Metamera. — The Gill-arches (Ribs of the Head). — Bones of the Two 
Pairs of Limbs. — Development of the Five-toed Foot, adapted for 
Walking, from the Many-toed Fin of the Fish. — The Primitive Fin 
of the Selachians {Archipterygium of Gegenbaur). — Transition of the 
Pinnate into the Semi-pinnate Fin. — Atrophy of the Rays or Toea 
of the Fins. — Many-fingered and Five-fingered Vertebrates. — Com- 
paiTson of the Anterior Limbs (Pectoral Fins) and the Posterior Limbfl 
(Ventral Fins). — Shoulder Girdle and Pelvis Girdle. — Germ-history of 
the Limbs. — Development of the Muscles. 

• In forming his estimate of my entire theory, the reader may begin with 
the details and examine the fundamental facts on which I base my con- 
elnsions. But it is equally necessary to connect the detached facts, and 
estimate their bearing on the whole. He who in the world of organisms seea 
only disconnected existencesj in which some organic similarities appear M 



2/4 THE EVOLUTION OF MAN. 

accidental ooinoidenoes, will remain a stranger to the reanlts of this 
inyestigation j not merely because he does not comprehend the concln- 
sions, but principally because the significance of the facts on which they 
are grounded, escapes him. A fact in itself is no more a scientific result, 
than a mere collection of facts is a science. That which makes a science 
of these facts, is their combination by that organizing mental faculty which 
determines the relations of the facts to each other." — Karl Gcoenbavk 
(1878). 

Among those features of the organization which are specially 
characteristic of the vertebrate tribe as such, the peculiar 
arrangement of the motive apparatus, or " locomotorium," 
undoubtedly occupies a principal place. As in all the 
higher animals, the active organs of motion, the muscles, 
form the most important part of this apparatus ; these are 
the fleshy bands which, by means of their peculiar contrac- 
tibility, of their power of contracting and shortening, move 
the various parts of the body, and thus change the position 
of the entire body. The arrangement of these muscles is, 
however, entirely peculiar in Vertebrates, and differs from 
the arrangement common to aU Invertebrates. 

In most lower animals, especially in Worms, we find 
that the muscles form a simple, thin flesh-layer immediately 
below the outer skin-covering. This " skin-muscle pouch " 
is most intimately connected with the skin itself, and the 
same feature occurs in the tribe of the Soft-bodied Animals 
{Mollusca). In the great group of the Articulated Animals 
(Arthropoda), in the Crab, Spider, Centipede, and Insect 
classes, we also find a similar feature, but with the difference 
that in these the skin-covering forms a hard coat of mail ; 
an inflexible skin-skeleton, formed of chitine, and often of 
carbonated chalk. This outer chitinous coat of mail is 
jointed in a great variety of ways both on the trunk and 



THE SKELETON. 275 

on the limbs of Articulated Animals, and th© muscular 
system, the contractile fleshy bands of which are attached 
to the inside of the chitinous tubes, is correspondingly 
jointed in an extremely varied manner. The case is exactly 
reversed in Vertebrates. In these alone an internal hard 
skeleton develops; an inner cartilaginous or bony frame 
to which the fleshy muscles are externally attached, and in 
which they find a firm support. This bony frame forms a 
combined lever-apparatus, a passive apparatus of motion. 
The hard parts of this, the arms of the lever, or the 
bones, are moored against each other by the active movable 
muscular bands, as by hawsers. This admirable locomotive 
apparatus, and especially its firm central axis, the vertebral 
column, is quite peculiar to Vertebrates, on account of which 
the whole group has long been called that of Vertebrates. 

This internal skeleton, notwithstanding the similarity of 
its first rudiment, has, however, developed so variously and 
characteristically in the difierent vertebrate classes, and in 
the higher classes forms so complex an apparatus, that 
Comparative Anatomy finds one of its richest mines in this 
feature. This was recoo:nized as lon^ acjo as the be^inninfr 
of the century by the older Natural Science, which at once 
seized these very welcome materials with peculiar pleasure. 
That science also, which is now called in the higher and 
more philosophical sense, " Comparative Anatomy," has 
reaped its richest harvest from this field. The Comparative 
Anatomy of the present day has studied the skeleton of 
Vertebrates more thoroughly, and revealed the laws of its 
formation more successfully, than has been the case with 
any other system of organs of the animal body. Here the 
well-known and oft-quoted passage, in which Gk)ethe 



2y6 THE EVOLUTION OF MAN. 

summed up the general result of his investigations in Mor- 
phology is especially appropriate : 

** All forms have a resemblance ; none is the same as another, 
And their choruB complete points to a mystical law." • 

Now that, by the Theory of Descent, we have discovered 
this " mystical law," have solved this " sacred enigma," now 
that we can explain the similarity of forms by Heredity, 
and their dissimilarity by Adaptation, we can find no 
weapon in the whole rich arsenal of Comparative Anatomy 
which defends the truth of the Theory of Descent more 
powerfully than the comparison of the internal skeletons 
of the various Vertebrates. We may, therefore, expect 
d priori that such comparison is of special importance in 
our History of the Evolution of Man. The inner vertebrate 
skeleton is one of those organs as to the Phylogeny of 
which Comparative Anatomy afibrds us conclusions far 
more important and deeper than those to be gained from 
its Ontogeny.^'® 

More than any other system of organs, the internal 
skeleton of Vertebrates, when studied comparatively, clearly 
and immediately impresses the observer with the necessity 
of the phylogenetic connection between these allied and yet 
very varied forms. A thoughtful comparison of the bony 
frame of Man with that of other Mammals, and of these 
again with that of lower Vertebrates, is alone sufficient to 
afibrd conviction of the true tribal relationship of all 
Vertebrates. All the separate parts of which this bony 
&ame is composed appear in other Mammals, in a great 

• •* AUe Gestalten sind ahnlioh, doch keine gleichet der andem; 
Und so deatet der Cbor auf ein geheimes Gesetz." 



IMPORTANCE OF THE SKELETON. 27; 

yariety of forms indeed, but yet in the same characteristic 
arrangement and relative position ; and if the comparison 
of the anatomical conditions of the skeleton is carried out 
below Mammals, we can prove that a direct and uninter- 
rupted connection exists throughout between these various 
forms which are apparently so utterly unlike, and can 
finally be traced from a most simple, common, fundamental 
form. These facts alone must fully convince every ad- 
herent of the Theory of Development that all Vertebrates, 
including Man, must be traced from a single common 
parent-form, from a Primitive Vertebrate; for the mor- 
phological features of the inner skeleton, and of the mus- 
cular system which stands in the closest correlative rela- 
tions to it, are of such a kind that it is quite impossible 
to conceive a polyphyletic origin, a descent from several 
different root-forms. It is impossible, on mature reflection, 
to accept the theory that the vertebral column with its 
various appendages, or the skeleton of the limbs with their 
variously differentiated parts, could have originated on 
several occasions during the course of the earth's history, 
and that, consequently, the various Vertebrates must be 
referred in various lines of descent from Invertebrates. 
Indeed, it is exactly in this point that Comparative Anatomy 
and Ontogeny irresistibly drive us to the monophyletic 
conclusion, that the human race is a very recent offshoot 
of the same great single trunk, from branches of which all 
other Vertebrates have also sprung. 

In order to obtain a view of the outlines of the develop- 
ment of the human skeleton, we must first take a general 
survey of its arrangement in the developed ]\Ian, (Cf 
Table XXXIV. and Fig. 251, the human skeleton from the 



( 2/8 ) 

TABLE XXXIV. 

Bjetem&tio Snrvey of the Arrangement of the Hnman SkeletooL 
A. Central Skeleton, or Axial Skeleton. Spine. 



A.». Vertebral Bodies and Upper Arches, 

1. Skall i 1 a. Pre- vertebral skull 
{Cranium) \ 2 b. Vertebral skull 

r 1 Neck vertebra 

2. Vertebral ] 12 Chest „ 
column -^ 5 Hip „ 

( Columna • 6 Vertebrae of the eacmm 
vertebralit) (.4 „ » „ tail (coccyx) 



A.b. Lower Vertebral Arches. 



1. Products of the gill- 
arches 



Producta arcuum 
branchialium 



2. Ribfl and bmct- Costee et itemtm 
bone 



B. Bones connecting the Extremities. 



B.a. Bones connecting the Anterior Limbs: 
Bones of the Shoulder. 

1. Shoulder-blade Scapula 
1. Primitive key-bone Procoracoidesf) 
[3. Raven Lone Coracoides f) 
4. Collar-bone, or key-bone Clavicula 


B.b. Bones connecting the Lower Limbs : 
Bones of the Pelvis. 

1. Intestinal bone Os ilium 

2. Pubic bone Os pubis 

3. Hip-bone Os ischi 



0. Jointed Skeleton of the Limbt. 



C.ft. Skekton of the Ftrre Limbs. 

I. F1B8T Division: Upper A km. 
1. Uppar arm bone Humerus 



II. Second Divimon ; 

3. Spoke-bone 
3. EU-bone 



Lower Arm. 

Radius 
Ulna 



in. Thibd Division : Hand. 



m. A. Wrirt 

Original parta 
/ a. Radical 
I b. TDtermedima 
\ c. Ulnar 
'Ld. Central 
i e. Carpal I. 

I/. „ n. 
] g. .. III. 
' *. „ IV. 



+ v. 



Carpus 
Modified parti. 
Scaphoideum 

 Liinatum 
 Triquetium 
 Intermedium f ] 
; Trapezium 
 Trapezoides 
 Capitatum 
Hamatum 



III. B. Palm of the Hand 
III. C. Five Fingem 
(14 booee 



Metacarpus (5) 

Digiti 

Phalanges) 



C.b. Skeleton of the Hind Limit. 

I. First Division: Thigh. 

1. Thigh-bone Femur 

II. Sboovd DrviBioir : Lso. 

2. Shin-bone Tibia 

3. Calf-bone Fibula 

III. TraBD Division: Foot. 



III. Ankle 
Original parts. 

a. Tibial 

b. Intormedium 

c. FibuLir 
. d. Central 

Tarsal I. 
., II. 
. .. III. 
. „ IV. + V. 



Tarsus 
Modified parte. 

'\ — Astragalus 

= Calcaneus 
= Navicular* 
- Cuneiform 



= Cuboides 



L 
IL 
UL 



1 



III. B. Sole of the Foot 

III. C. Five Toes 
(14 bones 



Metatarsits (5) 

Digiti 

Phalanges) 



HUMAN SKELETON. 



279 



^?i^'^ 





Fig. 251. 



Fig. 252. 



28o 



THE EVOLUTION OF MAN. 



I, 



Fig. 253.— 
Human vertebral 
colnmn (in an up- 
right position ; 
from the right 
side). (After H. 
Meyer.) 



right side (without arms); Fig. 252, the 
entire skeleton from the front.) In Man, 
as in all other Mammals, the skeleton is 
primarily distinguishable into the axial 
skeleton, or spine, and the skeleton of the 
appendages, or the bony frame of the limbs. 
The spine consists of the vertebral column 
and of the skull ; the latter being the pecu' 
liarly modified anterior part of the former. 
The ribs are the appendages of the vertebral 
column ; the tongue-bone (os Ungues), the 
lower jaw, and the other products of the 
gill-arches, are those of the skull. The 
skeletons of the two pairs of limbs, or ex- 
tremities, are composed of two different 
parts : of the bony frame of the actual, pro- 
minent extremities, and of the inner girdle 
skeleton, by which the limbs are attached 
to the vertebral column. The girdle skele- 
ton of the arms (or fore limbs) is the 
shoulder girdle ; the girdle skeleton of the 
legs (or the hind limbs) is the pelvic 
girdle. 

The bony vertebral column in human 
beings (coluriina vertehralis, or vertehra- 
rium. Fig. 253) is composed of thirty-three 
or thirty-four circular pieces of bone, which 
lie one behind the other (one above the 
other in the usual upright position of 
man). These bones {vertehroe) are sepa- 
rated from each other by elastic cushions. 



DEVELOPMENT OF THE SKELETON. 



281 



tlie intervertebral discs (iigamenta intervertebralia), and 
at the same time, are connected by joints, so that the 
entire vertebral column forms a firm and solid axis, which 
is, however, flexible and elastic, capable of moving freely 
in all directions. In the various regions of the trunk, 
the vertebrge differ in form and connection, so that the 
following are distinguished in the human vertebral column, 
beginning from above : seven neck- vertebrae, twelve breast- 
vertebrse, five lumbar-vertebrse, five cross-vertebrae, and 
four to five tail-vei*tebr8e. The uppermost, those directly in 






Fig. 254. — Third neck-vertebra of man. 
Fig. 255. — Sixth breast. vertebra of man. 
Fig. 256. — Second lumbar-vertebra of man. 



contact with the skull, are the neck-vertebrae (Fig. 254), 
and are distingTiished by a hole found in each of the 
two lateral processes. There are seven neck-vertebrae in 
Man, as in nearly all other Mammals, whether the neck 
is long, as in the Camel and the Girafie, or short, as in the 
Mole and the Hedo'ehog;. The fact that the number of these 
neck-vertebrae is always seven, — and there are but few 
exceptions (explicable by adaptation), — is a strong argu- 
ment for the common descent of all Mammals ; it can only 
be accounted for as a strict transmission from a common 



2SS THE EVOLUTION OF MAN. 

parent-form, from some Promammal which had seven neek> 
vertebrae. If each animal species had been a distinct crea- 
tion, it would have been far more to the purpose to have 
furnished the long-necked Mammalia with a larger, and the 
short-necked with a smaller number of neck- vertebrae. The 
neck-vertebrae are immediately followed by those of the breast 
or thorax, which, in Man and most other Mammals, number 
twelve or thirteen (usually twelve). Attached to the sides 
of each breast-vertebra (Fig. 255) is a pair of ribs — ^long 
curved processes of bone lying in and supporting the wall of 
the thorax. The twelve pairs of ribs, with the connecting 
intercostal muscles and the breast-bone {stemvm) constitute 
the breast-body {thorax, Fig. 252, p. 279). In this elastic 
and yet firm thorax lie the double lung, and between the 
two halves of this, the heart. The chest-vertebrae are 
followed by a short but massive section of the vertebral 
column, formed by five large vertebrae. These are the 
lumbar-vertebrae (Fig. 256), which bear no ribs and have 
no perforations in their lateral processes. Next conies the 
cross-bone (sacrum), which is inserted between the two 
halves of the pelvic girdle. This cross-bone consists of five 
fixed and amalgamated cross-vertebrae. Last comes a small 
rudimentary tail- vertebral column, the rump-bone (coccyx). 
This bone consists of a varying number (usually four, more 
rarely three or five) of small aborted vertebrae ; it is a 
useless rudimentary organ, retaining no physiological sig- 
nificance either in Man or in the Tail-less Apes or Anthro- 
poids. (Cf Figs. 204-208.) Morphologically it is, however, 
very interesting, as afibrding incontrovertible evidence oi 
the descent of Man and of Anthropoids from Long-tailed 
Apes. For this assumption afiords the only possible 



THE VEBTEBRJL 



283 



explanation of this rudimentary tail. In the human 

embryo, indeed, during the earlier stages of germ-history, 
the tail projects considerably. (Cf. Plate VII. Fig. M il., 
and Figs. 123, s, 124, s, vol. i. p. 370.) It afterwards becomes 
adherent, and is no longer CKternally visible. Yet traces 
of the aborted tail- vertebrae, as well as of the rudimentary 
muscles, which formerly moved them, persist throughout life. 
According to the earlier anatomists the tail in the female 
human being has one vertebra more than that of the male 
(four in the latter, five in the former).^''^ 



Ifuniber of VtrUbrce im variout Oatarhini. 



Neck 
Verte- 
bra. 



Tail- 
less 



(Man (Fig. 208) 

Orang (Fig. 205) 

Gibbon (Fig. 204) 

Gorilla (Fig. 207) 

Chimpanzee (Fig. 206) 



i Mandril (Mormon choras) 
Drill {Mormon leuco'phceus) ... 
Rhesus {Imius rhesus) 
Sphinx (Papio sphinx) 
Simpai (Semnopithecus melus) 



7 
7 
7 
7 

7 



7 
7 
7 
7 
7 



Chest 
or tho- 
racic 
Verte- 
bra. 



Lum- 
bar 

VerU- 
bra. 



12 
12 
13 
13 
14 



13 
12 
12 
13 
12 



5 
5 
5 
4 
4 



6 

7 
7 
6 
7 



Cfrott 
or 

tacral 
Verte- 
bra. 



mil 

Verte- 
bra. 



5 
4 

4 

4 

4 



3 
3 
2 
3 
3 



4 
5 
3 
6 
5 



Ittal. 



33 
33 
32 
33 
34 



5 

8 

18 

24 

31 



34 

37 
46 
53 
60 



The number of vertebrae in the human vertebral column 
is usually thirty-three in aU ; but it is an interesting fact 
that this number frequently varies, one or another vertebra 
failing, or a new, supernumerary vertebra inserting itself. 
Not unfrequently, also, a rib, capable of free motion, forms 
on the last neck-vertebra or on the first lumbar-vertebra, so 
that thus there are thirteen breast, and six neck, or four 
lumbar vertebrae. In this way contiguous vertebrae in the 
different sections of the vei-tebral column may replace each 



284 THE EVOLUTION OF MAN. 

» 

other. On the other hand, the above comparison of the 
number of vertebrae in different tail-less and tailed Catarhines 
shows considerable fluctuations in these numbers even 'n 
this one family.^'® 

To understand the history of the development of the 
human vertebral column, we must now study the form and 
combination of the vertebrae in somewhat greater detail 
The main outline of each vertebra is that of a signet ring 
(Figs. 254?-256). The thicker part, which faces the ventral 
side, is called the body of the vertebra, and it forms a short 
disc of bone ; the thinner forms a semi-circular arch — the 
vertebral arch, which is turned toward the dorsal side of the 
body. The arches of all the consecutive vertebrae are so con- 
nected by thin ligaments {ligamenta intercruralia) that the 
space enclosed by them all in common forms a long canal. 
In this spinal, vertebral canal lies, as we have seen, the hind 
portion of the central nervous system, the spinal marrow. 
The front part of this, the brain, is enclosed in the skull- 
cavity, and hence the skull itself is merely the anterior 
section of the vertebral column, modified in a peculiar way. 
rhe base or ventral side of the bladder-shaped brain-capsule 
was originally formed by a number of coalescent vertebral 
bodies, the amalgamated upper vertebral arches of which 
formed the arched or ventral side of the skull. 

While the firm, massive vertebral bodies constitute the 
true central axis of the skeleton, the dorsal arches serve to 
enclose and protect the central marrow. Analogous arches 
also develop on the ventral side as a protection for the 
thoracic and abdominal viscera. These inferior or ventral 
vertebral arches, proceeding from the ventral side of the 
vertebral bodies, form a canal in many low Vertebrates in, 



NATUBB OF THE VERTEBRfi. 385 

which are enclosed the large blood-vessels on the under 
surface of the vertebral column — the aorta and the tail vein. 
In higher Vertebrates most of these inferior vertebral arches 
are lost or become merely rudimentary. But in the breast 
section of the vertebral column they develop into strong, 
independent bony arches, the ribs (costce). The ribs are, in 
fact, merely large vertebral arches which have become 
independent, and have broken their original connection 
with the vertebral bodies. The gill arches, of which we 
have spoken so often, are of similar origin ; they are actual 
head-ribs in the strictest sense — processes which have 
actually originated from the lower arches of the skull- 
vertebrae, and which correspond with the ribs. Even the 
mode of connection of the right and left halves of the arches 
on the ventral side is the same in both instances. The 
chest is closed in front by the intervention, between the 
upper ribs, of the breast-bone (sternum) — a single bone 
originating from two corresponding side-halves. The gill- 
body is also closed in front by the intervention of a single 
piece of bone — the copula lingualis. 

In now turning from this anatomical examination of the 
constitution of the vertebral column to the question of its 
development, I may, as regards the first and most important 
features in the evolution, refer the reader to the explanation 
already given of the germ-history of the vertebral column 
(Chap. XIL, vol L pp. 369-378). In the first place, it is ne- 
cessary to recollect the important fact that in Man, as in all 
other Vertebrates, a simple, unarticulated cartilaginous rod 
at first occupies the place of the articulated vertebral column. 
This firm but flexible and elastic cartilaginous rod is the 
well-known notochord (chorda dorsalis). In the lowest Ver- 



286 



THE EVOLUTION OF MAN. 



tebrate, the Amphioxus, this persists throughout life in this 
very simple form, and penrianently constitutes the whole 
internal skeleton (Fig. 151, i,voL i. p. 420 ; Plate XI. Fig. 15). 
But even in the Mantle Animals (Tunicata), the nearest 
invertebrate allies of Vertebrata, we find this same noto 
chord; transitorily in the transient larval tail of Ascidia 
(Plate X. Fig. 5, ch) ; permanently in the Appendicularia 
(Fig. 162). The Mantle Animals, as weU as the Acrania, 
have undoubtedly inherited the notochord from a common 
worm-like parent-form, and these primaeval worm ancestors 
are the Chorda Animals (Chordonia, p. 91). 

Long before any trace of a skull, limbs, etc., appears in the 
human embryo or in that of any of the higher Vertebrates — 
in that early stage when the whole body is represented only 
y6 by the lyre-shaped germ-disc — in the cen- 
tral line of this latter, directly under the 
primitive groove or medullary furrow, ap- 
pears the simple chorda dorsalis. (C£ Figs. 
84-87, vol. i. pp. 297, 298, surface view; 
Figs. 66-70, 89-93, transverse section ; also 
Plates IV., v., ch.) As a cylindrical chord it 
traverses the longitudinal axis of the body, 
and is equally pointed at both ends. The 
cells which compose the chord (Fig. 257, b) 
Fig. 267.— PbT- come, in common with all the other ceUs of 
tion of notochord ^^^ skeleton, from the skin-fibrous layer 

(zhorda iAyrsaUs) of _ *' 

an embryo sheep : They most resemble certain cartilage cells ; 
a, sheath; b, cells, g^ special " chordaL tissuc " is often said to 

exist; but this must not be regarded as 
more than a special form of cartilaginous tissue. At an 
early period the notochord envelopes itself in a structureless 
sheath (a) as clear as glass, which is secreted by its cells. 




DEVELOPMENT OF THE VERTEBRAL COLUMN. 287 

This perfectly simple, inarticulate, primary axial 
skeleton is soon replaced by an axticulated, secondary 
axial skeleton, called the " vertebral column." On each side 
of the notochord the primitive vertebral bands or primitive 
vertebral plates (vol. L p. 306, Fig. 92, ww) differentiate from 
the inner portion of the skin-fibrous layer. The inner part 
of these primitive vertebral bands, which immediately sur- 
rounds the notochord, is the skeleton-plate, or skeleton 
stratum (i.e., the cell-layer forming the skeleton), which 
furnishes the tissue for the rudiments of the permanent 
vertebral column and of the skull. In the anterior half 
of the body the primitive vertebral plate remains a simple, 
continuous, unbroken layer of tissue, and soon expands into 
a thin- walled vesicle, which surrounds the brain ; this is the 
primordial skulL In the posterior half, on the contrar}^, 
the primitive vertebral plate breaks up into a number of 
homologous cube-shaped pieces, lying one behind the other , 
these are the several primitive vertebrae. The number 
of these is at first very small, but soon increases, as the 
germ grows in the posterior direction (Figs. 258-260, uw). 
The first and earliest primitive vertebrae are the foremost 
neck-vertebrae ; the posterior neck- vertebrae then originate ; 
then the anterior breast-vertebrae, etc. The lowest of the 
tail- vertebrae arise last. This successive ontogenetic growth 
of the vertebral column in a direction from front to rear 
may be explained phylogenetically by regarding the many- 
membered vertebrate body as a secondary product, which 
has originated from an originally inarticulate parent-form 
by progressive metameric development, or articulation. 
Just as the many-membered Worms (Earth-worm, Leech) 

and the closely allied Arthropods (Crabs, Insects) originally 
52 



288 



THE EVOLUTION OF MAN. 



*»'.<»• 




Figs. 258-260. — Lyre-sliaped germ-shield of a Chick, in three consecutive 
stages of development ; seen from the dorsal side ; enlarged about twenty 
times. Fig. 258, with six pairs of primitive vertebrae. The brain is a sim- 
ple bladder (hh). The spinal furrow from x remains wide open ; behind, at 
z, it is much enlarged, mp, Marrow-plates ; sp, side-plates ; y, limit be- 
tween the pharynx cavity (s/i) and the head-intestine (vd). Fig. 259, with 
ten pairs of primitive vertebrae. The brain has separated into three 
bladders: v, fore-brain; w, mid-brain; h, hind-brain; c, heart; dv, yelk- 
veins. The spinal furrow is still wide open (z). m/p, Marrow-plates. 
Fig. 260, with sixteen pairs of primitive vertebrge. The brain has separated 



PKIMITIVE VEllTEBR^. 289 

into ftre bladders : v, fore-brain ; z, twixt-brain j m, mid-bi-ain ; \, hind, 
brain ; n, after-brain ; o^ eye-vesicles ; g, ear-veeioles j c, heart j d«, yelk- 
reias ; mp, marrow-plate } uto, prinutive vertebra. 

developed from an inaxticulate worm-form by terminal 
budding, so the many-membered vertebrate body has 
originated from an inarticulate parent-form. The nearest 
extant allies of this parent-form are the Appendicularia 
(Fig. 162) and the Ascidian (Plate XI. Fig. 14). 

As has been repeatedly pointed out, this primitive 
vertebral, or metameric structure has a very important 
bearing on the higher morphological and physiological de- 
velopment of Vertebrates. (Cf. voL i. p. 346.) For the articu- 
lation is by no means confined to the vertebral column, but 
equally affects the muscular, nervous, vascular, and other 
systems. As is shown by the Amphioxus, the metameric 
structure appeared much earlier in the muscular than in 
the skeleton system. Each so-called primitive vertebra is 
in fact far more than the mere rudiment of a future verte- 
bra. In each primitive vertebra exists the rudiment of a 
segment of the dorsal muscles, of a pair of spinal nerve- 
roots, etc. Only the inner portion — that which lies directly 
next to the notochord and the medullary tube — is employed, 
as the skeleton-plate, in the formation of actual vertebrae. 
We have already seen how these true vertebrae develop from 
the skeleton-plate of the primitive vertebrae or metamera. 
The right and left lateral halves of each primitive vertebra, 
originally separate, unite. The ventral edges, meeting below 
the meduUary tube, surround the chord and thus form the 
rudiments of the vertebral bodies ; the dorsal edges, meeting 
above the medullary tube, form the first rudinicnts of the 
vertebral arches. (Cf Figs, 95-98, and Plate IV. Figs. 3-8.) 



290 



THE EVOLUTION OF MAN. 




Fig. 261.— Three 
breast-vertebn© of a 



In all Skulled Animals (Graniota), most of the soft, 
undifferentiated cells which originally constitute the 
skeleton-plate, afterwards change into cartilage ceUs, which 

secrete a firm, elastic "intercellular sub- 
stance," and thus produce cartilaginous 
tissue. Like most other parts of the 
skeleton, the rudimentary vertebrae soon 
pass into a cartilaginous condition, and, 
in the higher Vertebrates, the cartila- 
ginous tissue is afterwards replaced by 
the rigid bony tissue with its peculiar 
radiate bone-ceils (Fig. 5, vol. i. p. 126). 
The original axis of the vertebral column, 
human embryo of eight the notochord, is more or less compressed 

weeks, in lateral Ion- 1,1 l•^ • x* i-i 

gitudinal section : v, ^y ^^^^ cartilagmous tissuc which grows 
cartilaginous vertebral vigorously round it. In lower Verte- 
brates {i.e., in Primitive Fishes) a more 
or less considerable portion of the noto- 
chord remains within the vertebral 
bodies. In Mammals, on the contrary, it disappears almost 
entirely. In the human embryo, even at the end of the 
second month, the notochord is seen only as a thin thread 
which passes through the axis of the thick cartilaginous ver- 
tebral cu]umi\ (Fig. 261, ch). In the cartilaginous vertebral 
bodies themsjlves, which afterwards ossify, the thin remnant 
of the notochord (Fig. 262, clt) soon disappears entirely. A 
remnant remains, however, throughout life in the elastic 
'* intervertebral discs" which develop, from the skeleton 
plate, between each pair of vertebral bodies (Fig. 261, li). 
In a new-born child, a large, pear-shaped cavity, filled with 
a gelatinous cell-mass, is visible in each intervertebral disc 



bodies ; li, intervertO' 
bral discs ; ch, note 
chord. (After Koel 
liker.) 



EVOLUTION OF THE NOTOCHOKD. 



291 



(Fig. 263, a). This " gelatinous nucleus " of the elastic ver- 
tebral disc becomes less sharply defined, but persists 
throudiout life in all MamMals, while in Birds and Rep- 
tiles, even the last remnant of the notochord vanishes. 




Ftg. 262. — A breast-vertebra of the same embryo in lateral cross-section : 
cv, cartilaginous vertebral bodies ; cli, notochord ; pr, square process ; 
a, vertebral arch (upper) ; c, upper end of rib (lower arch). (After 
Koelliker.) 

Fig. 263. — Intervertebral disc of new-born child in cross-section : 
a, remnant of the notochord. (After Koelliker.) 

When the cartilaginous vertebrae afterwards ossify, the first 
deposit of bone-substance (the first "bone-nucleus") in 
the vertebral bodies is formed immediately round the rem- 
nant of the notochord, and soon completely displaces the 
latter. A special bone kernel or nucleus is then formed in 
each half of the cartilaginous vertebral arch. It is not till 
after birth that the ossification progresses so far that the 
three bone -nuclei approach each other. The two bony 
halves of the arch unite during the first year, but it is not 
till much later, till between the eighth and the twelfth 
year, that they unite with the bony vertebral body. 

The bony skull (craniu7ii\ which must be regarded as 



292 



TITE EVOLUTION OF MAN. 



the foremost, peculiarly modified section of the vertebral 
column, develops in an exactly similar manner. Just as, 
in the spinal column, the vertebral canal envelopes and pro- 
tects the dorsal marrow, so the skull forms a bony covering 
round the brain ; and, as the brain is merely the anterior, 
peculiarly differentiated portion of the dorsal marrow, we 
might conclude on a priori grounds, that the bony envelope ^ 
of the brain is a peculiar modification of that of the dorsal 
marrow. It is true, that if the developed human skull 
(Fig. 264) is considered by itself, it is impossible to under- 
stand how it can be merely the modified anterior portion of 
the vertebral column. It is a complex, capacious bony 
structure, consisting of no less than twenty bones, diflfering 

widely in form and size. Seven of 
these skull-bones constitute the 
spacious case which encloses the 
brain, and in which we distinguish 
the strong, massive floor of the skull 
(basis cranii) below, and the 
boldly arched roof of the skull 
(fornix cranii) above. The other 
thirteen bones form the "facia] 
skull," which especially provides the bony envelopes of 
the higher sense-organs, and at the same time as the jaw- 
skeleton, encircles the entrance to the intestinal canal. 
The lower jaw (usually regarded as the twenty-first 
skull-bone) is jointed to the skull-floor, and behind this, 
embedded in the roots of the tongue, we find the tongue- 
bone, which, like the lower jaw, has originated from the 
gill-arches, togetlijer with a portion of the lower arch, which 
originally developed as " skull-ribs " from the ventral side 
of the skuU-floor. 




Pig. 264. — Htunan skull, 
from the right side. 



VERTEBRAL THEORY OF THE SKULL. 293 

Although, therefore, the developed skull of the higher 
Vertebrates, in its peculiar form, its very considerable size, 
and its complex structure, seems to have nothing in 
common with ordinary vertebrae, yet the old comparative 
anatomists at the close of the eighteenth century correctly 
believed that the skull is originally merely a series of 
modified vertebrae. In 1790, Goethe " picked up out of the 
sand of the Jews' burying-ground among the downs near 
Venice, a dismembered skull of a sheep; he at once per- 
ceived that the face bones (like the three vertebrae of the 
back of the skull) are also derivable from vertebrae." And, 
in 1806, Oken (without knowing of Goethe's discovery), at 
Ilsenstein, on the way to the Brocken, " found a beautifully 
bleached skull of a hind ; the thought flashed through him, 
It is a vertebral column ! " ^'^^ 

For the last seventy years, this celebrated " Vertebral 
Theory of the Skull " has interested the most prominent 
zoologists ; the most important representatives of Compara- 
tive Anatomy have exercised their ingenuity in attempting 
to solve this philosophical skull-problem ; and the question 
has engaged attention in yet wider circles. It was not till 
1872 that the solution was found, after seven years of 
labour, by the comparative anatomist, who, both in the 
wealth of his real empirical knowledge and in the pro- 
fundity of his philosophic speculations, surpasses all other 
students of this science. Karl Gegenbaur, in his classic 
" Researches in the Comparative Anatomy of Vertebrates " 
(third part), showed that the skuU skeleton of the Selachii 
is the only record which affords definite proof of the verte- 
bral theory of the skuIL Earlier comparative anatomists 
erred in starting from the developed mammalian skull, and 



294 '"^E EVOLUTION OF MAN. 

in comparing the several component bones with the separate 
parts of vertebrae ; they supposed that in this way they 
could prove that the developed mammalian skull consists 
of from three to six original vertebrae. The hindmost of 
these skull-vertebrae was, according to them, the occipital 
bone. A second and a third vertebra were represented by 
the sphenoid bone, with the parietal bones, and by the 
frontal bone, etc. The elements of anterior skull vertebrae 
were even supposed to exist in the face bones. In opposi- 
tion to this view, Huxley first called attention to the fact 
that in the embryo this bony skull originally develops 
from a simple cartilaginous vesicle, and that in this simple 
cartilaginous " primitive skull " not the slightest trace of a 
constitution of vertebrate parts is visible. This is equally 
true of the skulls of the lowest and most ancient Skulled 
Animals (Graniota), the Cyclostomi and the Selachii. In 
these the skull retains throughout life the form of a simple 
cartilaginous capsule — of an inarticulate "primitive or 
primordial skull." K the older skull-theory, as it was 
accepted from Goethe and Oken by most comparative 
anatomists, were correct, then in these lowest Skulled 
Animals especially, and in the embryos of the higher Skulled 
Animals, the constitution of the " primitive skull " by a 
series of " skull-vertebrae " would be very clearly evident. 

This simple and obvious consideration, first duly em- 
phasized by Huxley, indeed overturns the famous " Verte- 
brate Theory of the Skull," as held by the older comparative 
anatomiflts. Yet the entirely correct fundamental idea 
holds good, i.«., the hypothesis that the skull develops from 
the anterior portion of the spinal column by differentiation 
and peculiar modification, just as the brain develops from 



HUXLEY'S SKULL THEOllY. 295 

the anterior portion of the dorsal marrow. But the true 
mode of empirically establishing this philosophic hypothesis 
was yet to be discovered ; and this discovery we owe to 
Gegenbaur.^^ He was the first to employ the phylogenetic 
method, which, in this as in all morphological questions, 
leads most surely and quickly to the result. He showed 
that the Primitive Fishes (Selachii, Figs. 191, 192, p. 113), 
as the parent-forms of all Amphirhina, yet retain per- 
manently in their skull-structure that form of primordial 
skull, from which the modified skull of the higher Verte- 
brates, and therefore that of Man, has developed phylo- 
geneticaUy. He also pointed out that the gill-arches of the 
Selachii show that their primordial skull was originally 
formed of a considerable number — at least nine or ten — 
primitive vertebrae, and that the brain-nerves, which branch 
from the base of the brain, entirely confirm this. These 
brain-nerves — with the exception of the first and the second 
pairs (the olfactory and the optic nerves) — are merely modi- 
fied spinal nerves, and, in their peripheric distribution, 
essentially resemble the latter. The Comparative Anatomy 
of these brain-nerves is one of the strongest arguments for 
the newer vertebral theory of the skulL 

It would lead us too far aside if we were to enter into 
the particulars of this ingenious theory of Gegenbaur, and 
I must content myself with referring to the great work 
already quoted ; in it the theory is fully demonstrated by 
empirical and philosophical arguments. The same author 
has giveji a brief abstract in his " Outlines of Comparative 
Anatomy " (1874), the study of which it is impossible to 
recommend too highly. In this work Gegenbaur indi- 
cates as original "skuU-ribs," or "lower arches of skull- 



296 THE EVOLUTION OF MAN. 

vertebrae,** in the selachian skull (Fig. 265), the following 
pairs of arches : I. and II. are two lip cartilages, of which 
the anterior (a) consists only of an upper, and the inferior 
(be) of an upper and a lower piece ; III., the jaw-arch, 
which also consists of two pieces on each side, — viz., the 
primitive upper jaw (os palato-qitadratum, o) and the 




Fig. 266. — Head skeleton of a I'limitivt^ Fish: n, nose. groove; eth,, regioL 
of the sieve-bone ; orh, eye-cavity ; la, wall of eai-labyriuth ; occ, occipital 
region of the primitive skull ; cu, vertebral column ; a, front ; be, hind lip- 
cartilage ; 0, primitive upper jaw (palato quadrcttum) ; u, primitive lower 
jaw ; II., tongue-arch ; III.-VIII., first to sixth gill-arohes. (After Gegen- 
baur.) 

primitive lower jaw (u); IV., the tongue arch (II.), and V. to 
X., six true gill arches, in the stricter sense of that term 
(III.-VIII.). The anatomical features of these nine or ten 
skull-ribs, or " lower vertebral arches," and of the brain 
nerves distributed over them, show that the apparently 
simple, cartilaginous " primordial skuU " of the Primitive 
Fishes originally develops from an equal number (nine at 
the least) of primitive vertebrse. The base of the skull is 
formed by the vertebral bodies ; the roof of the skidl by the 
upper vertebral arches. The coalescence an<l {una Igamation 
of these into a single capsule is, however, so ancient, that 



EVOLUTION OF THE SKULL. 



297 



their primordial separate condition now appears effaced by 
the action of the "law of abridged heredity," and is no 
longer demonstrable in the Ontogeny. 

In the human primitive skull (Fig. 26G), and in that of 
all higher Vertebrates, which has been moditied, phylog^ 
netically, from the primitive skull of the Sclachii, five con- 
secutive divisions are visible at a certain early period of 
development; these one might be tempted to refer to five 



Fig. 2GG. — Primitive skull of human 
embryo of four weeks; vertical S'-c-iion, 
the left half seen from the inside : v, z, 
m, h, n, the five grooves in the skull 
cavity, in which 1 in the five brain-bladders 
(fore-brain, twixt-brain, mid-brain, hind- 
brain, after-brain); 0, pear-shaped pri- 
mary ear-vesicle ; a, eye ; no, optic nerve ; 
p, canal of the hypophysist ; t, central 
part of the cranial basis. (After Koelliker.) 







original primitive vertebrae ; they are, however, merely the 
result of adaptation to the five primitive brain -bladders, 
arid, like the latter, they rather correspond to a larger 
number of metamera. TIi ; fact that the primitive verte- 
brate skull is a much moditied and profoundly transformed 
organ, and by no means a primitive structure, is also evi- 
dent in the circumstance that its rudiment, originally a soft 
membrane, commonly assumes the cartilaginous state only 
at its base and on the sides, while it remains membranous 
at the skull-roof Here the bones of the later bony skull 
develop in the soft membranous rudiment as an external 
bony roof, without a previous intermediate cartilaginous 
state, as in the base of the skull. Thus a great part of the 
skull-bones originally developed as roof-bones from the 



29S THE EVOLUTION OF MAN. 

leather-skin (corium), and only secondarily, come into closer 
relations with tlie skull. How, in Man, this most simple and 
primordial rudiment of the primitive skull develops, onto- 
genetically, from the head-plates, and how, in the mean- 
time, the anterior extremity of the notochord is enclosed in 
the base of the skull, has already been explained. (Cf 
vol i. p. 378; Figs. 145 and 146, p. 393.) 

The main features in the history of the development of 
tlie gill-arches, which must now be regarded as skull-ribs, 
lias been told. Of the four original rudimentary gill-arches or 
Mammals (Plates I. and VII., Figs. 232-236, p. 243), the first 
lies between the primitive mouth-opening and the first gili- 
opening. From the base of this gill-arch the " upper jaw 
process " develops, and this unites, in the manner already 
described, with the internal and the external nasal processes 
on each side, and forms the chief parts of the upper jaw skele- 
ton palate-bones, wing-bones, etc. (Cf p. 245 and 208.) The 
rest of the first gill-aich, now distinguished as the " lower-jaw 
process," forms out of its base two ear bonelets — the hammer 
(malleus) and the anvil (incus) ; the rest of its mass becomes 
a long strip of cartilage, called, after its discoverer, " Meckel's 
cartilage." On the external surface of this cartilage origin- 
ates, as a surface-bone (formed of cellular matter from the 
leather-plate), the permanent bony lower jaw. From the 
base of the second gill-arch in Mammalia originate the 
third eai" bonelet, the stirrup (stapes), and from the subse • 
quent parts, in order, the stirrup-muscle, the styloid process of 
the temporal bone, the styloid band, and the small horn of the 
tongue-bone. Finally, the third gill-arch becomes cartilagin- 
ous only at its anterior portion, and here, by the union of iUi 
two halves, is formed the body of the tongue-bone {cojmla 



BVOLUnON OF THE SKULL. 299 

hyoidea) and its great horn on each side. The fourth gill- 
arch appears in the mammalian embryo only as a transient, 
rudimentary embryonic organ, and does not develop into 
special parts. Of the posterior gill-arches (the fifth and 
sixth pairs), which are permanent in the Primitive Fishes, no 
trace is visible in the embryo of higher Vertebrates. The 
latter have long been lost. The four gill-openings in the 
human embiyo are also only interesting as transient rudi- 
mentary organs, which soon disappear entirely by concre- 
scence. The first gill-opening (between the first and second 
gill-arches) alone is of permanent importance ; from it 
develops the drum, or tympanic cavity of the ear, and the 
Eustachian tube. (Cf. p. 269, and Plate I., with explan- 
ation.) 

Not only did Gegenbaur, in his model " Researches into 
the Comparative Anatomy of Vertebrates," fii'st correctly 
explain the skull and its relation to the vertebral column, 
but he also first performed the no less weighty and interest- 
ing task of showing the phylogenetic derivation of the 
skeleton of the Hmbs in aU Vertebrates from one primordial 
form. Few parts of the body in the difierent Vertebrates 
are subjected, by adaptation to various circumstances, to 
such an infinite variety of modifications as the limbs, in 
point of size, form, and speciaL fitness for certain purposes, and 
yet we are now able to refer them all to one common here- 
ditary form. Vertebrates are distinguishable as regards the 
structure of their limbs into three large main groups. The 
lowest and most ancient Vertebrates, the skull-less and jaw- 
less classes, like all their invertebrate ancestors, had no 
paired limbs ; this condition is yet represented in the Am- 
phioxus and in the Cyclostomi (Figs. 189, 190). The second 



300 THE EVOLUTION OF MAN. 

main group consists of the two classes of true Fishes, and of 
(he DIpneusta ; in these, two pairs of lateral limbs, in the 
fsliape of many-fingered swimming-fins — one pair of pectoral 
tins (the fore legs) and one pair of abdominal fins (hind legs) — 
aio originally always present (Figs. 191, 192, Plate XII.). 
Finally, the third main group embraces the four higher 
vertebrate classes: Amphibia, Reptiles, Birds, and Mammals; 
in these the same two pairs of legs exist originally, but in 
the form of five-fingered feet. The digits or fingers are 
often fewer than five ; sometimes, also, the feet are quite 
aborted. But the original parent-form of the entire group 
had anteriorly and posteriorly five digits (Pentadactylism, 
p. 123). 

As regards the Phylogeny of the limbs, from their 
Comparative Anatomy it appears, therefore, that the extre- 
mities ori<^inated in the Fishes, in the Primitive Fishes 
(Selachii), and were transmitted from these to all higher 
Vertebrates (all the ATnphirhina), first in the form of 
many-fingered fins, and afterwards as five-fingered feet 
(Figs. 267-272). The anterior extremity — the pectoral fin 
(or the fore leg) — is originally shaped precisely like the 
posterior extremity — the ventral fin (or the hind leg). In 
the one, as in the other, the true limb, externally promi- 
nent, is distinguishable from the internal, concealed girdle, 
by which the limb is attached to the spinal column — the 
shoulder-girdle above, the pelvic girdle below. 

The genuine primitive form of the paired Umbs, as it 
existed in the most ancient of the Primitive Fishes during 
the Silurian Period, occurs to this day in perfect preserva- 
tion in the ancient Ceratodus, and very curious Mud-fish of 
Australia (p. 119, Plate XIL). In this, both the pectoral and 



THE LIMBS. 301 

the ventral fin is a flat, oval paddle, in which we find a 
feathered or biserial cartilaginous skeleton (Fig. 267). 
This skeleton consists firstly of a strong, articulated fin-rod 
or " stem " (Fig. 267, A B), which extends from the 3ase to 
the tip of the fin, and secondly, of a double row of thin, 
feathered rays (rr), which are attached to both sides of the 
central rod, like the pinnae of a pinnate leaf. This primi- 
tive fin, first recognized by Gegenbaur, and by him called 
the Archipterygium, is attached to the spinal column by 
means of a simple girdle in the shape of a cartilaginous 
arch.^^^ 

In some Sharks and Rays, especially when very young, 
this same primitive fin also occurs in a more or less modified 
form. But in most Primitive Fishes the fin is already 
essentially modified, in that the rays on one side of the stem 
are partly or altogether lost, and are retained only on the 
other side (Fig. 268). Hence arises the half-feathered, or 
uniserial fish-fin, inherited by the other fishes from the 
Selachii (Fig. 269). 

Gegenbaur first showed how the five-fingered leg of 
Amphibia is developed from this uniserial fin (Fig. 270) and 
is inherited by tluee classes of Amniota. In those Dip- 
Qeusta which were the ancestors of the Amphibia, the fin rays 
on the other side of the stem also were gradually degraded 
in development, and were in a great measure lost (the light- 
coloured cartilages in Fig. 269). Only the four lowest rays 
(shaded in Fig. 269) were retained ; and these are the four 
outer digits of the foot (second to fifth digits). The first, 
or great digit (toe), on the contrary, originated from the 
lower part of the fin-rod. From the middle and upper parts 
of this fin-rod developed the long main stem of the limbs 



302 



THE EVOLUTION OF MAN. 




Fig. 267. 



Fig. 269. 




Fig. 270. 




Fifi. 272. 



IVOLUnON OF THE LIMBS. 303 

Fio. 267. — Bones of pectoral fins of Ceratodus (Archipterygium, or 
bilateral pinnate skeleton) : A B, series of cartilaginous pieces forming the 
ventral stem of the fin ; rr, rays of the fin. (After Giinther.) 

Fig. 268. — Bones of pectoral fin of an earlier Primitive Fish ( Acanthias) . 
Most of the rays of the medial edge of the fin (B) have disappeared ; onlj 
a few (E*) remain. R R, rays of the lateral edge of fin ; mt, Metap. 
terygiam ; ms, Mezopterygiura ; p, Propteryginm. (After Gegenbaur.) 

Fig. 269. — Bones of pectoral fin of a more recent Primitive Fish, or 
Selachian. The rays of the medial edge of the fin have entirely dis- 
appeared. The shaded part on the right is that portion vrhich develops into 
the five-fingered hand of higher Vertebrates (h, the three basal pieces of 
the fin ; mtj Metapteryginm ; rudiment of the humerus ; ms, Mezoptery- 
gimn; p, Propteryginm). (After Gegenbaur.) 

Fig. 270. — Bones of the fore-limb of an Amphibian : h, upper arm 
(humerv^) ; r, u, lower arm (r, radius ; u, ulna) ; r, c, i, c, H,, root-bones of the 
hand, first row (r, radial ; i, intermediate ; c, central ; u, ulnary) ; 1, 2, 3, 4, 6, 
root-bones of the hand, second row. (After Gegenbaur.) 

Fig. 271. — Bones of hand of Gorilla. (After Huxley.) 

Fig. 272. — Bones of human hand, seen from the back. (After H. Meyer.) 



which is SO prominent in the higher Yertebrata as the upper 
arm (or leg) (Fig. 270, r and u) and the lower arm (or 

leg, h). 

The many-fingered fish -fins thus gave rise, by a process 
of gradual reversion and differentiation, to the five-fingered 
amphibian foot, which occurs first in the Sozobranchia, and 
which, from them, has been transmitted on the one hand to 
Reptiles, and to Mammals, up to Man, on the other (Fig. 272), 
Simultaneously with the reduction of the number of the fin- 
rays to four, a further differentiation afiected the fin-stem or 
rod ; it became transversely divided into the upper and 
lower arms (or legs), and a modification took place in the 
girdle, which in the higher Mammals originally consists, 
both anteriorly and posteriorly, of three bones. The simple 
arch of the original shuuldei-girdle separates, on each side 
into an upper (dorsal) piece — the shoulder-blade (scapula) 
53 



304 THE EVOLUTION OF MAN. 

and a lower (ventral) piece; the anterior portion of the 
latter constitutes the pro-key (or collar) bone (procbrcLcoi- 
deuTTh) and its posterior part the raven-bone (coracoideum). 
The simple arch of the pelvic girdle breaks up, correspond- 
ingly, into an upper (dorsal) piece — the intestinal bone 
(os ilium), and a lower (ventral) piece ; the anterior portion 
of the latter becomes the pubic bone (os pubis) and the 
posterior portion the hip-bone (os ischii). Table XXXIY., 
p. 278, shows the correspondence of these three parts of 
the pelvic girdle with those of the shoulder-girdle. The 
latter, however, in the key-bone or collar-bone (clavicula), 
possesses a fourth, wanting in the former. (Cf. Gegenbaur.^^ 
As in the girdle, so in the trunk of the limbs there is 
originally an absolute agreement between the anterior and 
posterior limbs. The first section of the trunk is supported 
by a single strong bone — in the anterior limbs, the upper 
arm (hu/merus) ; in the posterior, the upper leg (feviur). 
The second section, on the other hand, contains two bones — 
on the anterior extremity the spoke-bone (radius, Fig. 
270, r), and the ell-bone (ulna, Fig. 270, u) ; in the posterior 
the two corresponding bones, the shin-bone (tibia) and 
calf-bone (fibula). (Cf skeletons in Fig. 196 and Figs. 
204-208). Moreover, the subsequent small and numerous 
bones of the wrist (carpus) and of the ankle (tarsus) cor- 
respond ; so do the five bones of the middle of the hand 
(metacarpus) and of the middle of the foot (r)ietatar&iis). 
Finally, the same is true of the five digits attached to these 
parts, which in their characteristic structure of a series of 
bone-pieces correspond in the anterior and posterior limbs. 
Charles Martins, of Montpellier, an excellent morphologist 
haS' shown that, in detail, the anterior and posterior limbs 
conrospond.^^ 



HOMOLOGY OF THE LIMBS. 305 

As Comparative Anatomy thus shows that the skeleton 
of the limbs in Man is composed of the same bones, and in 
th(^ f^ame manner as the skeleton in the four higher verte- 
brate classes, we may justly infer their common descent 
from a single parent-form. This parent-form was the most 
ancient Amphibian possessing five digits both on the fore 
and on the hind limbs. The outermost part of the limbs 
has, indeed, been very much modified by adaptation to 
various conditions of life. The diversities in this point 
within the mammalian class are enormous. The slender 
limbs of the o^vift Deer and the strong, springy legs of the 
Kano^aroo, the climbing feet of the Sloth and the diffodng 
paws of the Mole, the fins of the Whale and the wings of 
the Bat, are all instances. It will, of course, be admitted by 
all that these organs of locomotion are as diverse as possible 
in point of size, form, and special function. And yet the 
internal bony skeleton is substantially the same in them alL 
In all these different forms of limbs the same characteristic 
bones are always represented in essentially the same strongly 
inherited combination ; and here we have a weighty confirm- 
ation of the theory of descent, such as is hardly afforded by 
the Comparative Anatomy of any other organ. (Cf. Plat^ 
IV. p. 34, voL ii. of " History of Creation.") True, in the 
limbs of the different Mammals, the skeleton is subject to 
various arrests of development and reversions, in addition 
to those due to special adaptation (Fig. 273). Thus, in the 
fore foot (or hand) of the Dog the first digit, or thumb, is 
aborted (Fig. 273 XL). In the Pig (III.) and the Tapir (V.) 
this digit has entirely disappeared. So, too, in the Rumi- 
nants (e.g., the Ox, Fig. IV.) the second and fifth digits are 
also aborted, and only the third and fourth are well deve- 



3o6 



THE EVOLUTION OF MAN. 



loped. Finally, in the Horse, only one digit, the third, is 
perfectly developed (Fig. VI., 3). And yet all these diverse 
fore-feet, as also the hand of the Ape (Fig. 271) and the 
human hand (Fig. 272j, have originated from the same 
common five-fingered parent-form. This is proved, not only 
by the rudiments of the aborted digits, but also by the 
homologous disposition of the wrist-bones (Fig. 273, a-p). 
(Vide supra, p. 124.) 

The same story is also told by the germ-history of the 
limbs, which is originally identical, not only in all Mammals, 
but in all Vertebrates. However difierent the limbs of the 
various Skulled Animals (Graniota) afterwards appear in 
their fully developed state, they nevertheless all originate 
from the same simple rudiment. (Cf. Plates VI. and VII., 





Fig. 273. — Skeleton of hand or fore-foot of six Mammals. I. Man; II. 
Dog; III. Pig; IV. Ox; V. Tapir; VI. Horse, r, Eadius; u, ulna; 
a, scaphoid ; h, semi-lunar ; c, triquetrum (cuneiform) ; d, trapezium ; ev 
trapezoid ; /, capitatum (unciform process) ; g, hamatum (unciform bone)> 
'P, pisiform ; 1, thumb ; 2, digit ; 3, middle finger ; 4, ring finger ; 5, little 
finger. (After Gegenbanr.) 



OSIQIN OF THE LIMBS. 30; 

voL L p. 362 ; / fore-leg, h, hind-leg.) In all, the first rudi- 
ment of each limb in the embryo is a simple wart, or small 
knob, which grows from the side of the body between the 
dorsal and ventral sides (Figs. 119 and 120, vol. i. pp. 357, 359 ; 
136 and 137, pp. 381, 382). The cells composing these knobs 
belong to the skin-fibrous layer. The outer surface is coated 
by the horn-plate, which is rather thicker at the apex of 
the protuberance (Plate IV. Fig. 5, x). The two anterior 
protuberances appear at a ratlier earlier period than the 
two posterior. By difierentiation of the cells, these simple 
rudiments develop immediately, in Fishes and in the 
Dipneusta, into fins. In the higher vertebrate classes, on 
the contrary, each of the four protuberances, in the course 
jf its development, assumes the form of a stalked plate, the 
'nner portion of which being narrower and thicker, the 
outer broader and thinner. The inner portion, or the handle 
of the plate, then divides into two sections : the upper and 
lower legs (or arms). Four notches then appear in the free 
edge of the plate, and these gradually become deeper ; these 
are the divisions between the five digits (Plate VIII, Fig. 1). 
The latter soon become more prominent. At first, however, 
all the five digits, both on the fore and on the hind limbs, 
are joined by a thin connecting web-like membrane; thi- 
recalls the original adaptation of the foot as a swimming-fin 
The further development of the limbs from this most simple 
rudiment takes place in the same way in all Vertebratets , 
that is, by the modification of certain groups of the cells of 
the skin-fibrous layer* into cartilage, of other groups into 
muscles, yet others into blood-vessels, nerves, etc. Probably 
the difierentiation of aU these various tissues occurs actuall}' 
in the limbs. Like the vertebral column and the skull, the 



308 THE EVOLUTION OF MAN. 

bony parts of the limbs are also formed at first from soft 
undifferentiated cell-groups of the skin-fibrous layer. These • 
afterwards change into cartilage, and from these the per* 
manent bones originate by a tertiary process.^®* 

The development of the muscles, or the active organs of 
locomotion, is, as yet, of much less interest than that of the 
skeleton, or the passive instruments of motion. The Com- 
parative Anatomy of these is, indeed, of much higher im- 
portance than their Embryology. But as very little attention 
has, as yet, been paid to the Comparative Anatomy and 
Ontogeny of the muscular system, we have only very 
general ideas of its Phjdogeny also. Tlie mii.sciilar systeu) 
as a whole has developed in the most intimate reciprocal 
correlation with the bone svstem.^^^ 



( 309 ) 



TABLE XXXV. 

Systematic Survey of the most Important Periods in the Phylggkny 

OF THE Human Skeleton. 

L First Period : Skeleton of the Chordonia (Fig. 187, p. 90). 
The entire skeleton is foiined by the notochord. 

II. Second Period : Skeleton of the Acrania (Fig. 189, p. 91). 

A notocliord-niembrane, tlie dorsal continuation of which fomui a cover 
ing roand the medullary tube, is formed round the notochord. 

in. Third Period : Skeleton of the CyclostonU (Fig. 190, p. 103). 

A cartilaginous primordial skull develops round the anterior extremity 
of the notochord, from the notochord-membrane. An outer cartila^nous 
gill-skeleton forms round the gills. 

IV. Fourth Period : Skeleton of the older Selachii (Fig. 268, p. 302). 

A primitive vertebral column, with upper and lower arches (the gill- 
arches and ribs) forms round the notochord. The remnant of the outer gill- 
skeleton remains with the inner. Two pairs of limbs, with pinnate (biaerial) 
skeletons, appear. 

V. Fifth Period : Skeleton of the more recent Selachii (Fig. 269, p. 302). 

The anterior gill-arches change into lip-cartilage and jaw-arches. The 
external gill-skeleton is lost. The skeleton of the two pairs of fins becomes 
uniserial (semi-pinnate). 

VI. Sixth Period : Skeleton of the Dipneusta (Fig. 2, Plate XH.). 
The skull becomes partially ossified j as does the shoulder-girdle. 

VII. Seventh Period : Skeleton of the Amphibia (Fig. 270, p. 302). 

The gill-arches are modified into parts of the tongue-bone, and of the jaw. 
apparatus. On the semi-pinnate skeletons of the fins the rays diminish in 
number to four, thus giving rise to the five«toed foot. The vertebral 
oolumn ossifies. 



3IO THE EVOLUTION OF MAN. 

Vin. Eighth Period : Skeleton of the Monotremata (Fig. 196, p. 148). 

The vertebral colnmn, skull, jaws, and limbs, acquire the definite 

oharaoteristics of Mammals. 

IX. Ninth Period : Skeleton of the MarsupiaUa (Fig. 197, p. 152). 

The coracoid bone of the shoulder.girdle becomes atrophied, and tba 
remnant of it amalgamates with the shoulder-blade. 

X. Tenth Period : Skeleton of the Semi-apes (Fig. 199, p. 164). 

The poaoh-bones, which distinguish Monotremes and Marsupials, 
disappear. 

.XI. Eleventh Period : Skeleton of the Anthropoid Apm 
(Figs. 204^208, p. 179). 

The skeleton acquires the peculiar development shared by Man ex. 
clusively with the Anthropoid Apes. 



CHAPTER XXIIL 

DEVELOPMENT OF THE INTESTINAL SYSTEM. 

Tix Primitive Intestine of the Gastmla. — Its Homology, or Morphological 
Identity in all Animals (excepting the Protoaoa). — Survey of the 
Structure of the Developed Intestinal Canal in Man. — The Moatb> 
cavity. — The Throat (pharynx). — The Gullet (oesophagus). — The "Wind- 
pipe (trachea) and Lungs. — The Larynx. — The Stomach. — The Small 
Intestine. — The Lirer and Gall-bladder. — The Ventral Salivary Gland 
(pancreas). — The Large Intestine. — The Rectum. — The First Rudiment of 
the Simple Intestinal Tube. — The Gastrula of the Amphioxos and of 
Mammals. — Separation of the Germ from the Intestinal Germ Vesicle 
(Gastrocystis). — The Primitive Intestine (Protogaster) and the After 
Intestine (Metagaster). — Secondary Formation of the Mouth and Anus 
from the Outer Skin. — Development of the Intestinal Epithelium from 
the Intestinal-glandular Layer, and of all other parts of the Intestine 
from the Intestinal-fibrous Layer, — Simple Intestinal Pouch of the 
Lower Worms. — Differentiation of the Primitive Intestinal Tube into a 
Eespiratory and a Digestive Intestine. — Gill-intestine and Stomach- 
Intestine of the Amphioxus and Ascidian.— Origin and Significance of 
the Gill-openings. — Their Disappearance. — The Gill-arches and the Jaw- 
skeleton. — Formation of the Teeth. — Development of the Lungs from the 
Swim-bladder of Fish. — Differentiation of the Stomach. — Development 
of the Liver and Pancreas. — Differentiation of the Small and Large 
Intestines. — Formation of the Cloaca. 

** Cautious people require us to confine ourselres to gathering material/ii 
and to leave it to posterity to luise a scientific structure from those 
materials ; because only in that way can we escape the ignjDminy of having 
the theories we believed in overthrown by the advance of knowledge. The 
unreasonableness of this demand is apparent enough from the faei that 



312 THE EVOLUTION OF MAN. 

Comparatire Anatomy, like every other science, is endless ; and therefore 
the endlessness of the accumulation of materials would nerer allow men, if 
they complied with this demand, to reap any harvest from this field. But, 
farther than this, history teaches us clearly, that no age in which scientific 
inquiry has been active, has been able so to deiiy itself, as, setting the goal 
of its researches in the future, to refrain from drawing conclusions for itself 
from its larger or smaller treasury of observations^ and from trying to fill the 
gaps with hypotheses. It would, indeed, be a hopeless proceeding, if, in 
order to avoid losing any part of our possessions, we should refuse to 
acquire any possessions whatever." — Kakl Ernst Baer (1819). 

Among the vegetative organs of the human body, to the 
development of which we now turn our attention, the intes- 
tinal canal is the most important. For the intestinal tube 
is the oldest of all the organs of the animal body, and 
carries us back to the earliest time of organological differ- 
entiation, to the first period of the Laurentian Epoch. As 
we have akeadv seen, the result of the first di^dsion of 
labour in the homogeneous cells of the earliest many-celled 
animal body must have been the formation of a nutritive 
intestinal canal. The first duty and the first need of every 
organism is self-support. This task is accomplished by the 
two functions of nutrition and of the covering of the body. 
When, therefore, in the primaeval collection of homogeneous 
cells (Synamoebium), of the phylogenetic existence of which 
we yet have evidence in the ontogenetic developmental 
form of the mulberry-germ {M uvula), the several , members 
of the community began to divide the work of life, they 
were first obliged to engage in two separate tasks. One 
half modified into nutritive cells, enclosing a digestive 
cavity, the intestinal canal ; the other half, on the contrary, 
developed into covering cells, forming the outer cover- 
ing of this intestinal canal, and, at the same time, of the 
whole body. Thus arose the first two germ-layers : the 



PRIMITIVE INTESTINAL CANAL. 



313 



inner, nutritive, or vegetative layer, and the outer, covering, 
or animal layer. 

If we try to construct for ourselves an animal body of 
the simplest conceivable form, possessing such a primitive 
intestinal canal, and the two primary germ-layers forming 
its wall, the result is necessarily the v:ry remarkable 
germ-form of the gastrula, which we have shown to exist 
in wonderful uniformity throughout the whole animal 




Fig. 274.— Gastrnla of a Chalk-spong^ (Olynthus) : Ay from outside; 
5, in longitudinal section through the axis ; g, primitive intestine ; 0, primi- 
tive mouth ; i, intestinal layer, or entoderm ; e, skin-layer, or exoderm. 

series : in the Sponges, Sea-nettles {Acalephoi), Worms, 
Soft-bodied Animals (i/o^Zusca), Aii:iculated Animals {Art/iro- 
poda), and Vertebrates (Figs. 174-179, p. 65). In all these 
various animal tribes the gastrula reappears in the same 
entirely simple form (Fig. 274). Its whole body is really 
merely the intestinal canal ; the simple cavity of the body, 
the digestive intestinal cavity, ii:. the primitive intestine 



314 ^tHE EVOLUTION OF MAX. 

(protogctder, g) ; its simple opening, tlie primitive mouth 
(protostoma, o), is at once mouth and anus ; and the two 
cell-strata which compose its wall, are the two primary 
germ-layers: the inner, the nutritive, or vegetative germ- 
layer, is the intestinal layer (entoderma, i) ; and the outer, 
covering layer, which, by means of its cilia, is also the agent 
of motion, is the animal layer, or skin-layer {exoderma, e). 
This highly important fact, that the gastrula appears as an 
early larval condition in the individual development of the 
most varied animals, and that this gastrula always exhibits 
the same structure, and that the very differently developed 
intestinal canals of the most varied animals, arises, onto- 
genetically, from the same extremely simple gastrula- 
intestine, this very important fact justifies, in accordance 
with the fundamental law of Biogeny, two conclusions, 
which involve important results, and of which one is general 
and one special. The general conclusion is an inductive 
one, and may be stated thus : The very variously formed 
intestinal canal of all the different Intestinal Animals 
has developed, phylogenetically, from one common and 
extremely simple primitive intestine, from the intestinal 
cavity of the Gastraea, that primaeval common parent-form 
which is at the present reproduced, in accordance with the 
fundamental law of Biogeny, in the gastrula. The second, 
the special conclusion, which is connected with the former, 
is deductive, and may be stated thus : The intestinal canal 
in Man as a whole is homologous with the intestinal canal 
in all other animals ; it has the same original significance, 
and has developed from the same rudimentary form.^^ 

Before proceeding to trace the history of the develop* 
ment of the human intestinal canal in detail, it will be 



THE HUMAN INTESTINAL CANAL. 315 

aeceflsaiy briefly to get a correct idea of the more 
general conditions of the formation of the intestinal canal 
in the developed Man. Not until this is known can the 
development of the several parts be correctly understood 
(Cf. Plates IV. and V., vol. i. p. 321.) The intestinal canal in 
the developed Man is, in all essential points, exactly similar 
in form to those of all other higher Mammals, and, especially, 
to that of the Catarhines, the Narrow-nosed Apes of the 
Old World. The entrance to the intestinal canal is the 
mouth-opening (Plate V. Fig. 16, o). Food and drink pass 
first through this into the mouth-cavity, in the lower part 
of which is the tongue. The human mouth-cavity is hedged 
with thirty-two teeth, attached in two rows to the two jaws, 
the upper and lower. It has already been stated that the 
series of teeth is formed in Man exactly as in the Catarhine 
Apes, but differs from the corresponding part in all other 
animals (p. 173). Above the mouth-cavity is the double 
nose-cavity ; the two parts of this are separated by the par- 
tition-wall of the palate. But, as we have seen, the nasal 
cavity is not originally separated at all from the mouth- 
cavity, a common nasal and mouth cavity being primarily 
formed in the embryo, and this separates at a later period 
into two separate stories by the hard palate-roof : the upper 
is the nasal cavity, the lower is the mouth-cavity. The nasal 
cavity is connected with certain air-filled bony cavities ; 
the jaw-cavities in the upper jaw, the frontal cavities in 
the frontal bone, and the sphenoid cavities in the sphenoid 
bone. Numerous glands of various kinds open into the 
mouth-cavity, particularly many small mucous glands and 
three pairs of large salivary glands. 

The human mouth-cavity is half closed at the back by 



3l6 THE EVOLUTION OF MAN. 

the vertical curtain which we call the soft palate, and in 
the centre of the lower part of which is situated the 
uvula. A glance with the mouth open into a mirror is 
sufficient to show the form. The uvula is 'of importance, 
because it occurs only in Men and in Apes. On both sides 
of the soft palate are the tonsils (tonsiUce). Through the 
gate-like arched opening situated beneath the soft palate, 
we pass into the throat-cavity (pharynx; Plate V. Fig. 
IG, sh), which lies behind the mouth-cavity. This is only 
partly 'visible in the open mouth when leflected in the 
mirror. Into the throat-cavity a narrow passage opens on 
each side (the Eustachian tube of tlie ear), Avhich leads 
directly into the tympanic cavity of the ear (Fig. 244, e, 
p. 260). The throat-cavity is continued into a long 
narrow tube, the gullet (oesojjJtagas, s/'). Through this 
the masticated and swallowed food passes down into the 
stomach. The wind-pipe {trachea, Ir) also opens into the 
upper part of the throat, and leads thence to the lungs. 
The opening of this is protected by the epiglottis, over 
which the food passes. The respiratory organs, the two 
lungs (Plate IV. Fig. 8, lu), are situated, in Man, as in all 
Mammals, in the right and left sides of the breast-cavity 
{thorax), and midway between them is the heart (Fig. 
8, hr, hi). At the upper end of the wind-pipe {trachea), 
below the epiglottis just spoken of, is a peculiarly differ- 
entiated section, the larynx, which is protected by a carti- 
laginous frame. The larynx *is the most important organ 
of the human voice and speech, and also develops from a 
part of the intestinal canal. In front of the larynx lies the 
thyroid gland {thyreoidea), which occasionally enlarges to 
the so-caUed " goitre." 



i 



THE HUMAN INTESTINAL CANAL. 



317 



The gullet (oesophagus) passes do^Ynward through the 
thorax, along the vertebral column, behind the lungs and 
the heart, and enters the ventral cavity, after penetrating 
the diaphragm. The latter (Fig. 16, 2;) is a membranous, 
muscular, transverse partition, which in all Mammals (and 
only in these) completely separates the chest-cavity 
{thorax, c) from the ventral cavity (c^J. As has been said, 
this division does not originally exist; at first a common 
chest and ventral cavity, the cceloma, or the pleuro- 
peritoneal cavity, is formed in the embryo. It is only 
afterwards that the diaphragm forms a muscular, horizontal 
partition between the chest and the ventral cavities. This 
partition then completely separates the two cavities, and 
is penetrated only by separate organs, passing through the 




Fig. 275. — Human stomach and gall-intestine in longitudinal section : 
a, cardia (limit of the oesophagus) ; b, fundus (blind sac of the left side) ; 
c, pylorus fold; d, pylorus valve; e, pylorus-cavity ; /g ^, gall-intestine ; 
i, mouth of the gall-duct and of the pancreas duct. (After H. Meyer.) 

chest-cavity into the ventral cavity. One of the most 
important of these organs is the gullet [oesophagus). After 
this has passed through the diaphragm into the ventral, 
cavity it enlarges into the stomach in which dioestion 



3l8 THE EVOLUTION OF MAX. 

especially takes place. The stomach of an adult man 
(Fig. 275, Plate Y. Fig. 16, mg) is an oblong sac, placed 
somewhat obliquely, the left side of which widens into 
a blind-sac, the base of the stomach or fundus (6), while the 
right side narrows, and passes at the right end, called 
the pylorus (e), into the small intestine. Between these two 
parts of the intestine is a valve, the pyloric valve {d), which 
only opens when the food-pulp (chyme) passes from the 
stomach into the small intestine. The stomach itseh" is the 
most important digestive organ, and serves especially to 
dissolve the food. The muscular wall of the stomach is 
comparatively thick, and, on the outside, has strong muscle- 
layers, which effect the digestive movements of the 
stomach ;— on the inside, it has a great number of small 
glands, the gastric glands, which secrete the gastric juice. 

Next to the stomach follows the longest part of the 
whole intestinal canal, the central, or small intestine 
(chylogaster). Its principal function is to effect the absorp- 
tion of the fluid mass 'of digested food, or the food-pulp 
(chyme), and it is again divided into several sections, the 
first of which, the one immediately following the stomach, 
is called the gall-intestine, or "twelve-finger intestine" 
(duodenum, Fig. 275, fg h). The gall-intestine forms a short 
loop curved like a horse-shoe. The largest glands of the 
intestinal canal open into it : the liver, the most important 
digestive gland, which furnishes the bile, or gall, and a very 
large salivary gland, the ventral saKvary gland, or pancreas, 
which secretes the digestive saliva. Both of these glands 
pour the juices they secrete, the bile and pancreatic juice, 
into the duodenum (i) near each other. In adults the liver 
UB a very large gland, well supplied with blood, lying on the 



THE HUMAN INTESTINAL CANAL. 319 

right side immediately below the diaphragm, and separated 
by the latter from the lungs (Plate V. Fig. 16, Ih), The 
pancreas lies somewhat further back and more to the 
left (Fig. 16, p). The small intestine is so long that it 
has to lie in many folds in order to find room in the limited 
space of the ventral cavity ; these coils are the bowels. 
They are divided into an upper intestine, called the empty 
intestine (jejunum), and a lower, the crooked intestine 
(ilii4m^). In this latter part lies that part of the small 
intestine at which, in the embryo, the yelk-sac opens into 
the intestinal tube. This long, thin intestine then passes 
into the large intestine, from which it is separated by a 
peculiar valve. Directly behind this " Bauhinian valve " 
the first part of the large intestines forms a broad pouch- 
like expansion, the blind intestine (coecum), the atrophied 
extremity of which is a well-known rudimentary organ, the 
vermiform process (processus vermiforTnis). The large 
intestine (colon) consists of three parts , an ascending part 
on the right, a transverse central part, and a descending 
part on the left. The latter finally curves like an S, called 
the "sigmoid flexure,*' into the last part of the intestinal 
canal, above the rectum, which opens at the back by the 
anus (Plate V. Fig. 16, a). Both the large intestine and 
the small intestine are furnished with numerous glands, 
most of them very small, and which secrete mucous and 
other juices. 

Along the greater part of its length the intestinal canal 
is attached to the inner dorsal surface of the ventral cavity, 
or to the lower surface of the vertebral column. It is 
fastened by means of the thin, membranous plate, called the 

mesentery, which develops directly under the notochord 

54 



320 THE EVOLUTION OF MAH. 

from the intestinal-fibrous layer, at the point where this 
curves into the outer lamina of the side-layer, into the 
skin-fibrous layer (Plate IV. Fig. 5, g). The curving-point 
was distinguished as the middle-plate (Fig. 99, mp). The 
mesentery is, at first, very short (Plate V. Fig. 14,^) ; but it 
soon lengthens considerably at the central part of the intes- 
tinal canal, and takes the form of a thin, transparent, 
membranous plate, which has to be the more extended the 
further the folds of the intestine diverge from the place 
where they are first attached to the vertebral column. The 
blood-vessels, lymphatic vessels, and nerves which enter 
the intestinal canal traverse this mesentery. 

Although, therefore, the intestinal canal; in the adult 
human being forms an extremely complex organ, and 
though it shows in its details so many intricate and delicate 
structural arrangements, — into which we cannot enter 
here, — this entire structure has developed, historically, 
from that simplest form of primitive intestine which 
was possessed by our gastrsead ancestors, and which the 
extant gastrula now exhibits. We have already shown (in 
Chapter YIII.) that the peculiar Hood-gastrula {Arajphi- 
gastrula) of Mammals (Fig. 277) may be referred back 
to the original Bell-gastrula (Archigastrtda) form, which, 
among Vertebrates, is now accurately retained solely by 
the Amphioxus (Fig. 276 ; Plate X. Fig. 10). 

Like the latter, the gastrula of Man and of all Mam- 
mals must be regarded as the ontogenetic reproduction 
of that phylogenetic evolution-form which we call the 
Gastrsea, and in which the whole body of the animal is 
intestine. 

The peculiar form and mode in which the complex 



DEVELOPMENT OF THE INTESTINAL CANAL. 



321 



human intestinal canal develops from the simple gastiaila 
and which is similar to that in other Mammals, can there- 
fore be only correctly understood when it is considered in 
the light of Phylogeny. We must, accordingly, distinguish 




Fig. 276. — Archigastrula of Amphioxns (in longitudinal secti(n): d, 
I'rimitive intestine; 0, primitive month; i, intestinal layer; e, skin-layc^o 

Fig. 277. — Amphigastrula of Mammal (in longitudinal section). Th.c 
primitive intestine (d) and primitive mouth (0) are filled up by 1\\2 cells of 
the intestinal layer (i) ; e, skin-layer. , 

« 

between the original p;:imary intestine ("the primitive 
intestine, or 'protogastev ") of the Skull-less Animals 
{Acrania), and the differentiated or secondary intestine 
( " after intestine, or metagaster " ) of the Skulled Animals 
(Craniota). The intestine of the Amphioxus (the repre- 
sentative of the Acrania) forms no yelk-sac, and develops, 
palingenetically, from the entire primitive intestine of the 
gastrula. The intestine of the Skulled Animals, on the 
other hand, has a modified, kenogenetic form of evolution, 
and differentiates at a very early period into two different 
parts : into the permanent secondary intestine, which alone 



322 THE EVOLUTION OF MAN. 

gives rise to the various parts of the differentiated intestinal 
system, and the transient yelk-sac, which serves only as a 
storehouse of materials for the building of the embryo. 
The yelk-sac attains its greatest development in Primitive 
Fishes {Selachii), Bony Fishes (Teleostei), Reptiles, and 
Birds. In Mammals, and especially in Placental Animals, 
it is atrophied. The peculiar intestinal development of the 
Cyclostomi, Ganoids, and Amphibia must be regarded as 
an intermediate form, between the palingenetic intestinal 
development of the Skull-less animals, and the kenoge- 
netic intestinal development of the Amnion Animals (Am- 
niota)}^ 

We have already seen in what a peculiar way the 
development of the intestine takes place ontogenetically in 
the human embryo and in that of other Mammals. Imme- 
diately from the gastrula of these originates a globular 
intestinal germ-vesicle (gastrocystis), filled with fluid (Figs. 
72, 73, vol L p. 289). In the waU of this is formed the 
lyre-shaped germ-shield, on the lower side of which, along 
the middle line, appears a shallow groove, the first rudi- 
ment of the future, secondary intestinal tube. 

This intestinal groove grows constantly deeper, and its 
edges curve toward each other, to grow together at last and 
form a tube (Fig. 100, vol i. p. 333). The waU of this 
secondary intestinal tube consists of two membranes of the 
inner, intestinal-glandular layer, and of the outer, intestinal- 
fibrous layer. The tube is completely closed at the ends, 
having only an opening in the centre of the lower waU, 
by which it is connected with the intestinal germ-vesicle 
(Plate V. Fig. l^). The latter, in the course of development, 
becomes continually smaller, as the intestinal canal continuei 



MmELOPMENT OF THE INTESTINAL CAKiJL 3^3 

fco grow larger and more perfect. While, at first, the intes- 
tinal tube appears only as a little appendage on one side of 
the great intestinal germ-vesicle (Fig. 278), the remnant of 
the latter afterwards forms only a very inconsiderable appen- 
dage of the great intestinal canal. This appendage is the 
yelk-sac, or navel-vesicle. It entirely loses its importance, 
and at length disappears, while the intestinal canal is finally 
closed at the original central opening, where it forms the 
so-called intestinal navel (Fig. 94, voL i. p. 312). 

It has also been said that this simple cylindrical intestinal 
tube, in Man as in aU Vertebrates, is at first entirely closed 
at both ends (Plate V. Fig. 14), and that the two permanent 
openings of the intestinal canal — at the anterior extremity, 
the mouth, at the posterior, the anus — ^form only second- 
arily, and from the outer skin. At the fore end, a shallow 
mouth-furrow originates in the outer skin, and this grows 
toward the blind, anterior end of the head intestinal cavity, 
into which it finally breaks. In the same way a shal- 
low furrow for the anus is formed behind in the skin, 
and this soon grows deeper, and grows toward the blind 
posterior end of the pelvic intestinal cavity, with which it 
finally unites. At both extremities there is, at first, a thin 
partition between the outer skin-furrow and the blind end 
of the intestine, and this disappears when the opening ie 
made.^^ 

Directly in front of the anus the allantois grows out of 
the posterior intestine; this is the important embryonic 
appendage which develops, in Placental Animals, and only 
in these (thus in Man too) into the placenta (Figs. 278, 279, / ; 
Plate V. Fig. 14, at). In this more developed form — repK - 
gented in the diagram (Fig. 94, 4, voL i. p. 312) — the intestina ' 



3^4 



THE EVOLUTION OF MAN. 



canal of Man, like that of all other Mammals, now forms a 
slightly-curved, cylindrical tube, which has an opening at 
both ends, and from the lower wall of which depend two 
sacs; the anterior navel-bladder, or yelk-sac, and the pos- 
terior allantois, or primitive urinary sac. 

Microscopic observation shows that the thin wall of this 
simple intestinal tube and of its two bladder-like append- 
ages is composed of two distinct cell-strata. The inner, 
which coats the entire cavity, consists of larger, darker cells. 




Fig. 278.— Human embryo of the third week, with the amnion and 
allantois. The great globular yelk-sac is below, the bladder-like allantois 
on the right ; there are as yet no limbs. The germ, with its appendages, is 
enclosed in the tufted membrane {chorion). 

Fig. 279. — Human embryo, with amnion and allantois, in the fourth 
week. (After Krause.) The amnion (w) lies pretty close to the body. The 
greater part of the yelk-sac (d) has been torn away. Behind this the allan- 
tois appears as a small pear-shaped bladder. Arms (/) and legs (h) are 
already commenced : v, fore-brain ; ;::, twixt-brain ; m, mid-brain ; h, hind- 
brain ; ?i, after-brain ; a, eye ; k, three gill-arches ; c, heart ; s, tail. 



mUDIMENT OF THE INTESTINAL CANAL. 325 

and ifl the intestinal-glandular layer. The outer stratum 
consists of lighter, smaller cells, and is the intestinal fibrous- 
layer. The cavities of the mouth and the anus are the only 
exceptions to this, because they originate from the outer 
skin. The inner cell-coating of the entire mouth-cavity is 
therefore famished, not by the intestinal glandular-layer, 
but by the skin-sensory layer, and its muscular lower layer, 
not by the intestinal-fibrous layer, but by the skin-fibrous 
layer. This is equally true of the wall of the anal cavity 
(Plate V. Fig. 15). 

If the question be asked, what relation these component 
germ-layers of the primitive intestinal wall bear to the 
infinitely varied tissues and organs which we afterwards 
find in the developed intestine, the answer is extremely 
simple. The relations of these two layers to the formation 
and difierentiation of the tissues of the intestinal canal with 
all its parts, may be condensed into a single sentence : The 
intestinal epithelium, that is, the inner, soft cell-stratum 
which coats the cavities of the intestinal canal and of all its 
appendages, and which directly accomplishes the nutritive 
process, develops solely from the intestinal-glandular 
layer ; on the contrary, aU other tissues and organs belong- 
ing to the intestinal canal and its appendages, proceed from 
the intestinal-fibrous layer. From this latter, therefore, 
originates the entire outer covering of the intestinal tube 
and its appendages j the fibrous connective tissue and the 
smooth muscles which compose its fieshy skin ; the carti- 
lages which support these, for example, the cartilage of the 
larynx and of the trachea ; the numerous blood and lymph 
vessels which absorb nutrition from the wall of the intestine; 
in shorty everything belonging to the intestine, with ih« 



326 THE EVOLUTION OF MAH. 

exception of tlie intestinal epithelium. From the intestinal* 
fibrous layer originates also the entire mesentery with all 
the adjacent parts, the heart, the large blood-vessels of the 
body, etc. (Plate V. Fig. 16). 

Let us now turn aside for a moment from this original 
rudimentary intestine of Mammals, in order to institute a 
comparison between it and the intestinal canal of those 
lower Vertebrates and Worms, which we have learned to 
recognize as the ancestors of Man. In the simplest Gliding- 

* ^^^ 

worm, or Turbellaria (Rhabdocoelum, Fig. 280), we find a 
very simple intestinal form. As in the gastrula, the intes- 
tine in these Worms is a simple pouch with a single open- 
ing, which latter acts both as mouth and anus (wi). The 
intestinal pouch has, however, differentiated into two sec- 
tions, an anterior throat-intestine (sd) and a posterior 
stomach-intestine (d). This differentiation becomes more 
important in the Ascidia (Fig. 281) and in the Amphioxus 
(Fig. 282), which connects the Worms with the Vertebrates. 
In these two animal forms the intestine is essentially 
identical; the anterior portion forms the respiratory giU- 
intestine, the posterior forms the digestive stomach-intes- 
tine. In both it develops, palingenetically, directly from the 
primitive intestine of the gastrula (Plate XI. Figs. 4, 10). 
But the original mouth-opening of the gastrula, or 
the primitive mouth, afterwards closes, and in its place is 
formed the later anus. In the same way, the mouth- 
opening of the Amphioxus and of the Ascidian is a new 
formation, as is the mouth-opening of Man, and generally, 
of aU Skulled Animals (Graniota). The secondary forma- 
tion of the mouth of the Lancelet is connected, as may be 
conjectured with some probability, with the formation oi 



EARLY FORMS OF THE INTESTINAL CANAL. 



.27 



the gill-openings, which appear directly behind it on the 
intestine. The front portion of the intestine has thus 




nnv 




Fig. 280. — A simple Gliding Worm (Rhahdoccelum) m, mouth; sd, throat- 
epithelium; sm, throat muscle-mass; d, stomiach-iiitestine ; nc, renal ducts; 
/, ciliated outer-skin ; nr)%, openings of the latter ; au, eye ; na, nose-pit. 

Fig. 281. — Structure of an Ascidian (seen from the left side, as in Plate 
XI. Fig. 14). The dorsal side is turned toward the right, the ventral side to 
the left ; the mouth-opening (0) is above ; at the opposite, tail end, the 
ascidian has become adherent. The gill-intestine {hr), perforated by many 
openings, extends into the stomach-intestine. The terminal intestine 
opens through the anus (a) into the gill-cavity (ci), from which the excre- 
ment is passed out with the respirated water through the gill-pore, or cloacal 
opening (a') ; m, mantle. (After Gegenbaur.) 



328 



THE EVOLUTION OF MAN. 



Ji 



mt' 



become a respiratory organ. I have already pointed out 
how characteristic this adaptation is of Vertebrates and 

Mantle Animals {Tunicata, p. 87). The 
phjlogenetic origin of the gill-openings in- 
dicates the beginning of a new epoch in 
the tribal history of Vertebrates. 

The most important process we meet 
with in the further ontogenetic development 
of the intestinal canal in the human embryo, 
is the origin of the gill-openings. At the 
head of the human embryo, the wall of the 
throat very early unites with the outer wall 
of the body, and four openings then form 
on the right and left sides of the neck, 
behind the mouth, and these lead directly 
from without into the throat-cavity. These 
openings are the gill-openings, and the par- 
titions separating them are the gill-arches 
(Figs. 116-118, vol. i. p. 356; Plates I. 
and v., Fig. 15, ks). These embryonic for- 
mations are very interesting ; for they show 

Fig. 282. — Lancelet (Amphioxus lanceolatus), double 
the natural size, seen from the left side (Lhe longi- 
tudinal axis is perpendicular, the mouth end above, 
the tail end below (as in Plate XI. Fig. 15) : a, mouth- 
opening, surrounded by bristles ; h, anal opening ; c, 
gill-pore ( porus hranchialis) ; d, gill-body ; e, stomach ; 
/, liver ; g, small intestine ; li, gill-cavity ; i, notochord, 
below which is the aorta; A-, aortal arch; /, main stem 
of the gill-artery ; m, swellings on the branches of 
the latter ; n, hollow vein ; o, intestinal vein. 



that all the higher Vertebrates when in a very young state, 



ORIGIN OF THE GILL-OPENINOS. 329 

reproduce, in accordance with the fundamental principle of 
Biogeny, the same process which was originally of the 
greatest importance to the development of the whole verte- 
brate tribe. This process was the differentiation of the 
intestinal canal into two sections : an anterior, respiratory 
part, the gill-intestine, which serves only for breathing, 
and a posterior, digestive part, the stomach -intestine, which 
serves only for digestion. As we meet with this very 
characteristic differentiation of the intestinal tube into two, 
physiologically, very distinct main sections, not only in 
the Amphioxus, but also in the Ascidian and the Appen - 
dicularia, we can safely conclude that it also existed in 
our common ancestors, the Chorda Animals (Ghordonia), 
especially as even the Acorn Worm (Balanoglossus) has 
it (Fig. 186, p. 86). All other Invertebrate Animals are 
entirely without this peculiar arrangement. 

The number of the gill-openings is stiU very large in the 
Amphioxus, as in Ascidians and in the Acorn Worm. In 
the Skulled Animals it is, on the contrary, very much 
lessened. Fishes mostly have from four to six pairs of gill- 
openings. In the embryos of Man and the higher Verte- 
brates also, only three or four pairs are developed, and these 
appear at a very early period. The gill-openings are perma- 
nent in Fishes, and afford a passage to the water which has 
been breathed in through the mouth (Figs. 191, 192, p. 113; 
Plate V. Fig. 13, ks). On the other hand, the Amphibians 
lose them partially, and aU the higher Vertebrates entirely. 
In the latter, only a single vestige of the giU-openings remains, 
the remnant of the first gill-opening. This changes into a 
part of the organ of hearing ; from it originates the outer 
ear-canal, the tympanic cavity, and the Eustachian tub > 



( 330 ) 



TABLE XXXVI. 

BjiiMinHn Sorrey of the Development of the Human InteBtinal Sjstem, 
VJi. — The parts nuirked thoB f are processes from the intestinal tnbe. 



flMt buUh seotion 
of the 

Intestinal 

System : 

Mm Respiratory 

Intestine 
(Gill Intestine). 

PnooASTEB. 
MqMTdUortus.) 



/ 



1. 



Month-oavlly 



Nose-cavity 
{Cavumnaat) 



a 

Seoend main 
Motion of the 

Intestinal 

System: 

Digestive 

Intestine 

(Stomach Intev* 

tine). 

PSFTOOASTBX. 



5. 



Mentk-^eaiag 

Lipa 
Jaws 
Teeth 

Tongue 

Tongue bone 
f Salivary glan^ 

Soft palate 
' Uvula 

Noee canal 
•f Jaw cavities 
+ Frontal cavities 
,j Ethmoid cavity 



IIsthmoB of the thiMt 
Tonsils 
PharjTix 
+ Eustachian tube 
f Tympanic cavity 
+ Brain-appendage 
•j- Thyroid gland 



Lnng-cavity 
( CavumpKimoni*) 



(i 



Anterior Intestine j 
(^Protogaster) 1 



f Larynx 
 Windpipe 
Longs 

Gullet 

Stomach-openliig 
Stomach 
Stomach exit 



6. 



Central Intestine 
{Muogast0r) 



I Gal 
fLh 

fPai 



Posterior Intestlae 

{EpigatUr) 



Urinary Intestiae 
(I^<ui«r) 



Gall-intestine 
 Liver 
Pancreas 
Empty intestine 
|(f Yelk-sac, or n*Tel- 
bladder) 
Crooked intestine 

Large intestine 
■f- Blind intestine 
f Vermiform prooeis al 
the ccBcuoi 

Rectum 

Anal opening 

( ("f Primitive urinary mo 
\ T Urinary tube 
UOdaeiyUadte 



JStmaerii 

MaxiXUz 

DenUs 

Lingua 

Os hyoidea 

GlandulcB talivaUs 

Velum -palatinum 

Umda 

Meatus narium 
Sinus maxUiara 
Sinus frontdUs 
Sinus ethwutidaUs , 

Isthmus faueivm 

TonsilloR 

Pharynx 

ThiiHJL Bustachii 

Cavum tympani 

Hypophysis 

Thyrecid/ea 

Larynx 
Trachea 
Pulmonu 

(EsophaguB 
Cardia 
Stomachut 
Pylorus 

Duodcnvm 

Bepar 

Pancreas 

Jejunum 

( Vesicula umbiliei^- 

lU) 
Hewn 



Golan 
Coecum 

Processus 
formis 
Rectum, 
Anus 

AOantoia) 
Urethra 



vermt' 



i 

4J K 



■2 a 

^ to 



a> 



"« 4) 
I- 

fe'S 



Coo 
•I— 



_a ID 

I® 



1^ 



I 



THE MOUTH-SKELETON. 331 

We have already considered this remarkable formation, and 
will only caU attention once more to the interesting fact that 
the human middle and external ear is the last remnant 
of the gill-opening of a Fish. The gill-arches, also, which 
separate the gill-openings, develop into very various parts. 
In Fishes they remain permanently as giU-arches, carrying 
the respiratory gill-tufts ; so also in the lowest Amphibia ; 
but in the higher Amphibia they undergo various modifica- 
tions in the course of development, and in aU the three 
higher vertebrate classes, thus also in Man, the tongue-bone 
(os hyoides) and the bonelets of the ear originate from th« 
giU-arches. (Cf. Plates VI. and VII.) 

From the first gill-arch, from the centre of the inner 
surface of which the muscular tongue grows, proceeds 
the rudimentary jaw-skeleton ; the upper and lower jaws 
which enclose the cavity of the mouth and carry the 
teeth. The Acrania and Monorhina are entirely destitute 
of these important parts. They first appear in the genuine 
Fishes, and have been transmitted by these to the higher 
Vertebrates. The original formation of the human mouth- 
skeleton, of the upper and lower jaws, can thus be traced 
back to the earliest Fishes, from which we have inherited 
them. The teeth originate from the outer skin-covering 
which covers the jaws ; for, as the formation of the whole 
mouth-cavity takes place from the outer germ-layer, the teeth 
must, of course, also have developed originally from the skin- 
layer. This can be actually proved by close microscopic 
examination of the most delicate structural features of the 
teeth. The scales of Fishes, especially of Sharks, are, in 
thk respect, exactly similar to their teeth (Fig. 288). Thus 
the human teeth, in their earliest origin, are modified fish- 



v^^ 



THE EVOLUTION OF MAN. 



scales. ^^ On similar grounds we must regard the salivary 
glands, which open into the mouth-cavity, as really outer- 
skin (epidermic) glands, which have not developed, like the 
other intestinal glands, from the intestinal-glandular layer 
of the intestinal canal, but from the outer skin, from the 
horn-plate of the outer germ-layer. It is evident that, as 
the mouth develops in this way, the salivary glands must 
be placed genetically in the same series with the sweat, 
sebaceous, and milk glands of the epidermis. 

The human intestinal canal is 
therefore quite as simple in its 
original formation as the primitive 
intestine of the gastrula. It also 
resembles that of the lowest Worms. 
/ It then differentiates into two sec- 
,,|v tions, an anterior gill-intestine, and 
Jj a posterior stomach-intestine, like 
the intestinal canal of the Lancelet 
and the Ascidian. By the develop- 
ment of the jaws and gill-arches 
it is modified into a true Fish- 
intestine. Afterwards, however, the 
gill-intestine, which is a memorial 
of the Fish-ancestors, as such, is 
entirely lost. The parts that remain 
Shark (Centrcphorus calceus). take a wholly different form ; but 

Oneachrhomboid bone-tablet, j^Q^^|^}jS^a^jj(^ijig that the anterior 
lying in the leather-skin, rises . • , , • i i j.i 

a small, three-cornered tooth, section of our intestinal canal thus 
(After Gegenbaur.). surrenders entirely its original 

form of gill-intestine, it yet retains its physiological func- 
tion as a respiratory intestine; for the extremelj in- 




FiG. 283. — Scales of a 



THE BREATHING APPARATUS. 333 

teresting and remarkable discovery is now made that even 
the permanent respiratory organ of the higher Vertebrates, 
the air-breathing lungs, has also developed from this anterior 
section of the intestinal canal. Our lungs, together with 
the wind-pipe (trachea) and the larynx, develop from the 
ventral waU of the anterior intestine. This entire great 
breathing-apparatus, which occupies the greater part of 
the chest (thorax) in the developed Man, is at first merely 
a very small and simple vesicle or sac, which grows out 
from the intestinal canal immediately behind the gills, and 
soon separates into two lateral halves (Figs., 284, c, 285, c ; 
Plate V. Figs. 13, 15, 16, lu). This vesicle occurs in all 
Vertebrates except in the two lowest classes, the Acrania and 
CyclostomL In the lower Vertebrates, however, it develops, 
not into lungs, but into an air-filled bladder of considerable 
size, occupying a great part of the body-cavity (coeloma), 
and which is of quite a difierent significance from the 
lungs. It serves, not for breathing, but as an hydrostatic 
apparatus: for vertical swimming movements it is the 
swimming-bladder of Fish ; but the lungs of Man and of 
all other air-breathing Vertebrates develop from the same 
simple bladder-like appendage of the anterior intestine, 
which, in Fishes, becomes the swimming-bladder. 

Originally this sac also has no respiratory function, but 
serves only as an hydrostatic apparatus, augmenting or 
diminishing the specific gravity of the body. Fishes, in 
which the swimming-bladder is fully developed, are able to 
compress it, and thus to condense the air contained in il 
The air sometimes also escapes from the intestinal canal 
through an air-passage which connects the swimming- 
bladder with the throat (pharynx), and is expelled through 



334 



THE EVOLUTION OF MAK. 



the mouth ; in this way the circumference of the swim- 
ming-bladder is diminished, and the fish becomes heavier 
and sinks. When the animal is again about to ascend, 
the swimming-bladder is distended by remitting the com- 





FiG. 284. — Intestine of an embryonic Dog (which is representev^ in Fig. 
137, vol. i. p. 382; after Bischoff), from the ventral side : a, gill-arches (four 
pairs) ; 6, rudimentary throat and larynx ; c, lungs ; d, stomach ; /, liver ; g, 
walls of the opened yelk-sac, into which the central intestine opens by a 
wide aperture ; /i, rectum. 

Fig. 285. — The same intestine, seen from the I'ight side : a, lungs ; t, 
stomach ; c, liver ; d, yelk- sac ; e, rectum. 

pressing force. This hydrostatic apparatus begins to be 
transformed into a respiratory organ in the Mud-fishes 
(Dipneusta), the blood-vessels in the wall of the swim- 
ming-bladder no longer merely separating air, but also 
inhaling fresh air, which has come in through the air- 
, passage. This process is fully developed in all Amphibia. 
The original swimming-bladder here generally becomes a 



ITOLUTION OF THE LUNQflL 335 

long, and its air-passage a wind-pipe. The amphibian lung 
has been transmitted to the three higher vertebrate classes, 
and even in the lowest Amphibia the lung on either side 
is as yet a very simple, transparent, thin-walled sac — as, 
for instance, in our common Water-Newts, or Tritons, and 
very like the swimming-bladder of Fishes. The Amphibia 
have, it is true, two lungs, a right and a left; but in 
many Fishes also (in the ancient Ganoids) the swim- 
ming-bladder is double, the organ being divided into a 
right and a left half On the other hand, the lung of the 
Ceratodus is single (p. 119). The earliest rudiment of the 
limg in the human embryo and in the embryo of all higher 
Vertebrates is also a simple, single vesicle, which does not 
separate till afterwards into a pair of halves — the right and 
the left lung. At a later period, the two vesicles grow con- 
siderably, occupy the greater part of the chest cavity, and lie 
one on each side of the heart ; even in Frogs we lind that the 
simple sac, in the course of its development, is transformed 
into a spongy body of a peculiar, froth-like texture. This 
lung-tissue develops as a tree-like, branched gland, bearing 
berry-like appendages. The process by which the lung-sac 
was attached to the anterior intestine, which was originally 
very short, lengthens, by simple growth, into a long thin 
tube ; this tube is the wind-pipe (trachea) ; it opens above 
into the throat (pharynx), and below divides into two 
branches which pass into the two lunga In the wall of the 
wind-pipe ring-shaped cartilages develop, which keep the 
whole distended ; at the upper end of this wind-pipe, below 
its entrance into the throat, the larynx, the organ of voice 
and speech, develops. The larynx occurs even in Amphibia 
in very various stages of development, and with the aid o£ 

55 



33^ THE EVOLUTION OF MAM. 

» 

Comparative Anatomywe can trace the progressive develop 
ment of this important organ from its very simple rudiment 
in the lower Amphibia up to the complex and vocal appara- 
tus represented by the larynx of Birds and Mammals. 

Though these organs of voice, speech, and air-respiration 
develop so differently in the various higher Mammals, they 
yet all arise from the same simple original rudiment — 
from a vesicle which grows out of the wall of the anterior 
intestine. We have thus satisfied ourselves of the interest- 
ing fact that both the respiratory apparatus of Vertebrates 
develop from the fore part of the intestinal canal ; first, the 
primary and more primitive water- respiring apparatus, the 
gill-body, which is altogether lost in the three higher 
vertebrate classes ; and, afterwards, the secondary and more 
recent air-breathing apparatus, which acts in Fishes only 
as a swimming-bladder, but as a lung from the Dipneusta 
upwards. 

We must say a few words about an interesting rudi- 
mentary organ of the respiratory intestine, the thyroid 
gland (thyreoidea), the large gland situated in front of the 
larynx, and below the so-called " Adam's apple," and which, 
especially in the male sex, is often very prominent ; it is 
produced in the embryo by the separation of the lower wall 
of the throat (pharynx). This thyroid gland is of no 
use whatever to man; it is only aesthetically interesting, | 
because in certain mountainous dis^xicts it has a tendency 
to enlarge, and in that case it forms the " goitre " which 
hangs from the neck in front. Its dysteleological interest 
is, however, far higher ; for as Wilhelm Miiller of Jena 
has shown, this useless and unsightly organ is the last 
remnant of the " hypobranchlal groove," which we hiiv© 



THE STOMACH. 337 

already considered, and which, in the Ascidia and in the 
Amphioxus, traverses the middle of the gill-body, and is of 
great importance in conducting the food into the stomach 
(voL i. p. 420; Plate XI. Figs. 14-16, y)}^ 

The second main section of the intestinal canal, the 
stomach or digestive intestine, undergoes modifications no 
less important than those affecting the first main section. 
On tracing the further development of this digestive section 
of the intestinal tube, we again find a very complex and 
composite organ eventually produced from a very simple 
rudiment. For the sake of rendering the matter more 
intelligible, we may distinguish the digestive intestine 
into three parts: the fore intestine (with the gullet and 
stomach) ; the middle intestine, the gall-intestine (with the 
liver and pancreas) ; the empty intestine (jejunv/m), and 
jrooked intestine (ileus); and the hind intestme (large 
aatestine and rectum). Here we again find protuberances 
or appendages of the originally simple intestinal tube 
which change into very various structures. We have 
already discussed two of these appendages — the yelk-sac, 
which protrudes from the middle of the intestinal tube 
[Fig 286, c), and the allantois, which grows out of the 
last portion of the pelvic intestine as a large sac-Hke 
piotuberance (w). The protuberances from the middle 
of the intestine are the two great glands which open 
;nto the duodenum, the liver (h) and the ventral salivary 

gland. 

Immediately behind the bladder-like rudiment of the 
lungs (Fig. 286, i) comes that portion of the intestinal' tube 
which forms the most important part of the digestive 
apparatus, viz., the stomach (Figs. 284, d, 285, h). This sac- 



338 



THE EVOLUTION OF MAN. 



shaped organ, in which the food is especially dissolved and 
digested, is not so complex in structure in the lower Verte- 
brates as in the higher. Thus, for instance, in many Fishes, 
it appears as a very simple spindle-shaped expansion at the 




Fig. 286. — Longitudinal section througli an embryonic Chick on the 
fifth day of incubation : d, intestine ; o, mouth ; a, anus ; I, lungs ; h, liver ; 
g, mesentery ; v, auricle of heart ; k, ventricle of heart ; h, arterial arches ; 
J, aorta; c, yelk-sac; w, yelk-duct; u, allantois ; r, stalk of allantois; n, 
amnion ; w, amnion-cavity ; s, serous membrane. (After Baer,) 



beginning of the digestive section of the intestine, which 
latter passes from front to rear in a straight line under the 
spinal column in the central plane of the body. In Mam- 
mals the rudiment of this organ is as simple as it thus 
is permanently in Fishes . but at a very early period the 
various parts of the stomach-sac begin to develop unequally. 
As the left side of the spindle-shaped pouch grows much 
more vigorously than the right, and as, at the same time, 



DEVELOPMENT OF THE STOMACH. 



339 



there occurs a considerable obliquity of its axis, it soon 

assumes an oblique position. The upper end lies more to 

the left and the lower end more 

to the right. The anterior end 

extends so as to form the long 

narrow canal of the gullet 

{oesophagus) ; below the latter, 

the blind-sac of the stomach 

{fundus) bulges out to tlie left, 

and thus the later form of the 

stomach is gradually developed 

(Fig. 287, e ; Fig. 275, p. 317). The 

axis, which was originally verti- 

FiG. 287. — Human embryo of five 
weeks, from the ventral side ; opened 
(enlarged). The breast wall, abdominal 
wall, and liverj have been removed. 3, 
external nasal process ; 4, upper jaw ; 6, 
lower jaw ; z, tongue ; v, right, v', left 
ventricle of heart ; o', left auricle of 
heart ; b, origin of aorta ; h' h" h'", Ist, 
2nd, 3rd aorta-arches ; c c' c", hollow 
vein ; ae, lungs {y, lung-arteries) ; e, 
stomach ; m, primitive kidneys (j, left 
yelk- vein ; s, pylorus ; a, right yelk- 
artery ; n, navel-artery ; n, navel-vein) ; 
X, yelk-duct ; i, terminal intestine ; 8, 
tail; 9, fore-limb ; 9', hind-limb. (After 
Coste.) 

cal, now inclines from a higher point on the left to a lowei' 
on the right, and continually acquires a more transverse 
direction. In the outer stratum of the stomach-wall, and 
from the intestinal-fibrous layer, develop the strong muscles 
which perform the powerful digestive movements. In 




340 THE EVOLUTION OF MAIC. 

the inner stratum, on the contrary, innumerable minor 
glands develop from the intestinal-glandular layer. These 
are the peptic glands, which supply the most important 
digestive fluid — the gastric juice. At the lower extremity 
of the pouch of the stomach a valve develops, which, as 
the pylorus, separates the stomach from the small intestine 
(Fig. 275, d). 

The disproportionately long middle intestine, or small 
intestine, now develops below the stomach. The develop- 
ment of this section is very simple, and is essentially caused 
by a very rapid and considerable longitudinal growth. 
Originally this section is very short, straight, and simple ; 
but immediately below the stomach a horseshoe bend, or 
loop, begins to appear at a very early period in the intestinal 
canal, simultaneously with the separation of the intestinal 
tube from the yelk-sac and with the development of the 
mesentery. (Cf Plate V. Fig. 14, ^r, and Fig. 186, vol. i. p. 381.) 
Before the abdominal wall closes, a horseshoe-shaped loop of 
intestine (Fig. 136,771) protrudes from the ventral opening of 
the embryo, and into the curve of this the yelk-sac or navel - 
bladder opens (n). The thin, delicate membrane which 
secures this intestinal loop to the ventral side of the vertebral 
column, and occupies the inside of this horseshoe curve, is 
the first rudiment of the mesentery (Fig. 286, g). The most 
prominent part of the loop into which the yelk-sac opens 
(Fig. 287, x), and which is afterwards closed by the intestinal 
navel, represents that part of the small intestine which is 
afterwards called the crooked intestine (ileum). Soon a 
very considerable growth of the small intestine is observ- 
able ; and in consequence, this part has to coil itself in many 
Loops. The various parts of the small intestine which we 



THE SMALL INTESTINE. 341 

• 

have yet to distinguisli differentiate later in a very simple 
way; these are the gall-intestine (duodenwin), which is 
next to the stomach, the long empty intestine (jejunum) 
which succeeds, and the last section of the small intestine, 
the crooked intestine (ileuvi). 

The two large glands which we have already named, the 
liver and the ventral salivary gland, grow out, as protuber- 
ances, from the gall-intestine, or duodenum. The liver first 
appears in the form of two small sacs, situated right and left 
just behind the stomach (Figs. 284,/, 285, c). In many low 
Vertebrates the two livers remain quite separate for a long 
time (in the Myxinoides for life), and coalesce only imper- 
fectly. In higher Vertebrates, on the other hand, the two 
livers coalesce more or less completely at an early period, 
and constitute one large organ. The intestinal-glandular 
layer, which lines the hollow, pouch-like rudiment of the 
liver, sends a number of branched processes into the investing 
intestinal-fibrous layer ; as these solid processes (rows of 
gland-cells) again branch out, and as their branches coalesce, 
the peculiar netted structure of the developed liver is 
produced. The liver-cells, as the secreting organs which 
form the bile, all originate from the intestinal-glandular 
layer. The fibrous mass of connective tissue, which joins 
this great cellular network into a large compact organ, and 
which invests the whole, comes, on the other hand, from the 
intestinal-fibrous layer. From the latter originate also the 
great blood-vessels which traverse the entire liver, and 
the innumerable netted branches of which are interlaced 
with the network of the liver-cells. The gall-ducts, which 
traverse the entire liver, collecting the bile and discharging 
it into the intestine, originate as intercellular passages along 



342 



THE EVOLUTION OF MAN. 



the axis of the solid cell-cords ; they all discharge into the 
two primitive main gall or biliary ducts, which originate 
from the base of the two original protuberances of the 
intestine. In Man, and in many other Vertebrates, these 
two ducts afterwards unite, and form one simple gall-duct, 
which discharges into the ascending portion of the gall- 
intestine. The gall bladder originates as a hollow pro- 
tuberance of the right primitive liver duct. The gi^owth 
of the liver is at first exceedingly rapid ; in the human 
embryo, even in the second month, it attains such dimen- 
sions that during the third month it occupies by far the 
largest part of the body-cavity (Fig. 288). At first, both 




Fig. 288. — Chest and abdominal viscera of a 
human embryo of twelve weeks, in natural size. 
( After Koelliker. ) The head is omitted ; the chest 
and abdominal walls removed. The greater part 
of the abdominal cavity is occupied by the liver, 
from an opening in the centime of which the blind- 
intestine {coecum, v), with the worm appendage, 
protrudes. Above the diaphragm the heart is 
visible in the centre, with the small lungs on the 
right and left. 



halves are equally well developed ; afterwards the left half 
lies considerably behind the right. In consequence of the 
asymmetrical developm-ent and alteration in the position of 
the stomach and other abdominal viscera, the whole of the 
liver is eventually forced over on to the right side. Although 
the growth of the liver is, afterwards, not so excessive, even 
at the end of gestation, it is comparatively much larger in 
the embryo than in the adult. In the latter, its weight 



THE LARGE INTESTINS. 343 

in proportion to that of the whole body is as 1 : 36 ; in the 
former, as 1:18. The physiological significance of the liver 
during embryonic life — which is very great — depends espe- 
cially on the part it plays in the formation of blood, and 
less on its secretion of bile. 

From the gall-intestine, immediately behind the liver, 
grows another large intestinal gland, the ventral-salivary 
gland, or pancreas. This organ, which occurs only in 
Skulled Animals, also develops as a hollow sac-shaped 
protuberance of the intestinal wall. The intestinal-glan- 
dular layer of the latter sends out branching shoots, which 
afterwards become hollow. The ventral-salivary gland, just 
like the salivary glands of the mouth, develops into a large 
and very complex gland shaped like a bunch of grapes. 
The outlet of this gland (ductus pancreaticus), through 
which the pancreatic juice passes into the gall-intestine, 
seems to be at first simple and single ; afterwards it is 
often double. 

The last section of the intestinal tube, the terminal 
intestine or large intestine (epigaster), in mammalian 
embryos, is, at first, a very simple, short, and straight tube, 
opening posteriorly through the anus. In the lower Ver- 
tebrates it retains this form throughout life. In Mammals, 
on the other hand, it grows to a considerable size, coils, and 
difierentiates into different sections, of which the foremost 
and longest is called the colon, the shorter and hinder the 
rectimi. At the commencement of the former a valve 
(vcdvula Bauhini) forms, which divides the large intestine 
from the small intestine ; behind appears a pouch-like 
protuberance, which grows larger and becomes the blind- 
intestine (coecumi) (Fig. 288, v). In plant-eating Mammals 



344 TH^ EVOLUTION OF MAN. 

this becomes very large, while in those which eat flesh it 
remains very small, or is entirely aborted. In Man, as in 
most Apes, the beginning of the blind intestine alone 
becomes wide ; its blind end remains very narrow, and 
afterwards appears only as a useless appendage of the 
former. This " vermal appendage *' is interesting in dys- 
teleology as a rudimentary organ. Its only importance in 
Man consists in the fact that now and then a raisin-stone, 
or some other hard, indigestible particle of food becomes 
lodged in its narrow cavity, causing inflammation and 
suppuration, and, consequently, killing individuab other- 
wise perfectly healthy. In our plant-eating ancestors this 
rudimentary organ was larger, and was of physiological 
value. 

Finally, w© must mention another important appendage 
of the intestinal tube; this is the urinary bladder (uro- 
eystis) with the urinary tube (urethra), which in develop- 
ment and in morphological character belong to the intestinal 
system. These urinary organs, which act as receptacles and 
excretory passages for the urine secreted by the kidneys, 
originate from the inner part of the allantois-stalk. The 
allantois develops, as a sac-like protuberance, from the 
anterior wall of the last section of the intestine (Fig. 286, u). 
In the Dipneusta and Amphibia, in which this blind-sac 
first appears, it remains within the body-cavity (coeloma), 
and acts entirely as a urinary bladder. In aU Amniota, on 
the other hand, it protrudes considerably out of the body- 
cavity of i^e embryo, and forms the large embryonic 
" primitive urinary sac," which, in higher Mammals, forms 
the placenta. At birth this is lost ; but the long allantois- 
stalk (r) remains, its upper portion forming the central navel 



•raE URINABY BLADDER. 34$ 

band of the urinary vesicle (ligamentum vesico-^mhilicale 
medium), a rudimentary organ which extends as a solid 
cord from the top of the urinary bladder to the navel. The 
lower part of the allantois-pedicle (the " urachus ") remains 
hollow, and forms the urinary bladder. At first, in Man, 
as in the lower Vertebrates, this organ discharges into the 
last section of the posterior intestine, and there is, there- 
fore, a true " cloaca," receiving both urine and excrement ; 
but, among the Mammals, this cloaca is permanent only in 
the Cloacal Animals, or Monotremes, as in Birds, E-eptiles, 
and Amphibia. In all other Mammals (Marsupialia and 
Placentalia) a transverse partition forms at a later period, 
and separates the urinary-sexual aperture in front from the 
anal aperture behind, (Cf Chapter XXV.) 



( 346 ) 



EXPLANATION OF PLATE I.— (Frontispiece.) 

Development or the Face. 

The twelve figures in Plate I. represent the faces of four different 
Mammals in three distinct stages of individual evolution : Mi-Miii that of 
Man, Bi-Biii of the Bat, Ci-Ciii of the Cat, Si-Siii of the Sheep. The 
three different stages of evolution have been chosen to correspond as far as 
possible ; they have been reduced to about the same size, and are seen from 
in front. In all the figures the letters indicate the same : a, eye ; v, fore- 
brain ; m, mid-brain ; s, frontal process ; fe, nose-roof ; o, upper jaw process 
(of the first gill-arch) ; u, lower jaw process (of the first gill-arch) ; h, 
second gill-arch ; d, third gill-arch ; r, fourth gill-arch ; g, ear-fissun' 
(remains of the front gill-opening) ; z, tongue. (Cf . Plates VI. and VII., 
Pigs. 232-236, p. 243 ; also Figs. 123, 124, vol. i. p. 370.) 



TABLE XXXVII. * 

Systematic Survey op the most Important Periods in thi 
Phylogeny of the Human Intestinal System. 

I. First Period : Intestine of Gastrcea (Figs. 274-277 ; Plate V. Figs. 9, 10). 
The whole intestinal system is a simple pouch (primitive intestine), the 
eixnple cavity of which has one orifice (the primitive mouth). 

n. Second Period : Intestine of the Scolecida (Plate V. Fig. 11). 
The simple intestinal tube widens in the middle into the stomach, and 
acquires, at the end opposite to the primitive mouth, a second opening 
(primitive anus) ; as in the lower Worms. 

[IT. Third Period: Intestine of Chorda Animals (Fig. 281 ; Plate V. Fig. 12). 

The intestinal tube differentiates into two main sections — the respiratory 
intestine with gill-openings (gill-intestine) in front, the digestive intestine 
with stomach-cavity (stomach-intestine) behind ; as in Ascidia. 



i 



SURVEY OF HUMAN INTESTINAL SYSTEM. 



347 



IV. Fourth Period : Intestine of Skull-less Animala {Acra/nta) 
(Fig. 282 ; Plate XI. Fig. 15). 
The gill-streaks appear between the gill-openiDgs of the respiratory 
intestine ; a liver blind.sao grows from the stomach-pouoh of the digestire 
intestine ; as in the Amphioxru. 

V. Fifth Period : Intestine of CyelosUma (Plate XI. Fig. 16). 
The thyroid gland develops from the ciliated grooTe on the base of 
the gills (hypobranchial groove). A compact liver-gland develops from 
the liver blind-sac. 

VI. 8i«Bth Period : Intestine of Primitive Fishes (p. 114). 
Cartilaginous gill-arches appear between the gill-openings. The fore- 
most of these form the lip-cartilages and the jaw-skeleton (upper and lower 
jaw). The swimming-bladder grows from the pharynx. The ventral-salivary 
gland appears near the liver, as in Selachii. 

VII. Seventh Period : Intestine of Dipneusta (p. 118). 
The swimming-bladder modifies into the lungs. The mouth-cavity 
becomes connected with the nose-cavity. The urinary bladder grows from 
the last section of the intestine, as in Lepidosiren. 

Vni. Eighth Period: Intestine of Amphibia (p. 126). 

The gill-openings close. The gills are lost. The larynx originates from 
the upper end of the trachea. 

IX. Ninth Period : Intestine of Monotremes (p. 145). 
The primitive mouth and nasal cavity is separated by the horizontal 
palate-roof into the lower mouth-cavity (food passage) and the upper nose- 
cavity (air passage) ; as in all Amnion Animals 

X. Tenth Period: Intestine of Marsupials (p. 149). 
nie existing cloaca is separated by a partition wall into an anterior 
urinary-sexual aperture and a posterior anal aperture. 

XI. Eleventh Period : Intestine of Cata/rhine Apes (p. 176). 
All parts of the intestine, and especially the teeth-apparatus, acquire the 
ohaxaoteristio development common to Man and Gatarhine Apes. 



CHAPTER XXIV. 

DEVELOPMENT OF THE VASCULAR SYSTEM. 

Application of the Fundamental Law of Biogeny. — The Two Sides. — Heredity 
of Conservative Organs. — Adaptation of Progressive Organs. — Ontogen}/ 
and Comparative Anatomy complementary of each other. — New 
"Theories of Evolution" of His. — The "Envelope Theory" and the 
"Waste-rag Theory." — Main Germ and Supplementary Germ. — Former, 
tive Yelk and Nutritive Yelk. — Phylogenetic Origin of the latter from 
the Primitive Intestine. — Origin of the Vascular System from the 
Vascular Layer, or Intestinal-fibrous Layer. — Phylogenetic Siguificanoe 
of the Ontogenetic Succession of the Organ-systems and Tissues. — 
Deviation from the Original Sequence ; Ontogenetic Heterochronism. — 
Covering Tissue. — Connective Tissue. — Nerve-muscle Tissue. — Vascular 
Tissue. — Relative Age of the Vascular System. — First Conmiencemeni 
of the Latter ; Coeloma. — Dorsal Vessel and Ventral Vessel of Worms: 
— Simple Heart of Asoidia. — Atrophy of the Heart in the Amphioxus. — 
Two-chambered Heart of the Cyclostoma. — Arterial Arches of the 
Selachii. — Double Auricle in Dipneusta and Amphibia. — Double Ven- 
tricle in Birds and Mammals. — Arterial Arches in Birds and Mammals. 
Germ-history (Ontogeny) of the Human Heart.; — FftraUelism of the 
Tribal-history (Phylogeny). 

"Morphological oomparison of the adult conditions ahonld naturally 
precede the study of the earliest conditions. Only in this way can the 
investigation of the history of development proceed in a definite direction j 
it is thus provided, as it were, to see each step in the formative process in 
its true relation with the condition which is finally to be reached. Treat- 
ment of the histoxy of derelopment without preparatory study is (mlj too 



APPLICATION OP THE LAW OF BIOGENY. 349 

likely to lead to groping in the dark ; and it not unfrequently leadg to the 
most unfortnnate results — far inferior to those which might be established 
beyond question without any study of the history of development," — 
Albxandkb Brauk (1872). 



In applying to Organogeny the fundamental law of Bio- 
geny, we have already afforded some conception of the 
degree in which we may follow its guidance in the study of 
tribal history. The degree differs greatly in the different 
organ-systems ; this is so, because the capacity for trans- 
mission on one side, and the capacity for modification on 
ifhe other, vary greatly in the different organs. Some parts 
of the body cling tenaciously to the inherited germ-history ; 
and, owing to heredity, accurately retain the mode of 
evolution inherited from primaeval animal ancestors j other 
parts of the body, on the contrary, exhibit very small 
capacity for strict heredity, and have a great tendency to 
assume new kenogenetic forms by adaptation, and to modify 
the original Ontogeny. The former organs represent, in the 
many-celled community of the human organism, the con- 
stant or conservative; the latter, on the contrary, the 
changeable or progressive element of evolution. The mutual 
interaction of both elements determines the course of his- 
torical evolution. 

Only to the conservative organs, in which Heredity pre- 
ponderates over Adaptation, in the course of tribal evolu- 
tion, can we directly apply the Ontogeny to the Phylogeny, 
and can infer, from the palingenetic modification of the 
germ-forms, the primaeval ^letamorphosis of the tribal forms. 
In the progressive organs, on the contrary, in which Adap- 
tation has acquired the ascendency over Heredity, the 
original course of evolution has, usually, been so changed. 



350 THE EVOLUTION OF MAK. 

vitiated, and abbreviated, in the course of time, that w© 
can gain but little certain information as to the tribal- 
history from the kenogenetic phenomena of their germ- 
history. Here, therefore, Comparative Anatomy must come 
to our help, and it often affords much more important and 
trustworthy disclosures as to Phylogeny than Ontogeny 
is able to impart. It is, therefore, most important, if the 
fundamental law of Biogeny is to be correctly and critically 
applied, to keep its two sides continually in view. The 
first haif of this fundamental law of evolution enables us to 
use Phylogeny, as it shows us how to gain an approximate 
knowledge of the history of the tribe from that of the 
germ : the germ-form reproduces, by Heredity, the corre- 
sponding tribal form (Palingenesis). The other half of 
the law, however, limits this guiding principle, and calls 
attention to the foresight with which it must be employed ; 
it shows us that the original reproduction of the Phylogeny 
in the Ontogeny has been in many ways altered, vitiated, 
and abbreviated, in the course of millions of years. The 
germ-form has deviated, by Adaptation, from the corre- 
sponding tribal form (Kenogenesis) ; the greater this devia- 
tion, the more are we compelled to employ Comparative 
Anatomy in the study of Phylogeny. 

Perhaps in no other system of organs of the human body 
is this so greatly the case as in the vascular system (vas- 
cular, or circulatory apparatus), the development of which 
we wiU now examine. If we attempted to infer the 
original structural features of our older animal ancestors 
solely from the phenomena which the individual develop- 
ment of these organ-systems, in the embryo of Man and of 
other high Vertebrates, exhibit, we should obtain wholly 



HIS ON THE VASCULAR SYSTEM. 351 

erroneous views. By many influential embryonic adap- 
tations, among which the development of an extensive 
nutritive yelk must be regarded as the most important, the 
original course of development of the vascular system has 
been so altered, vitiated, and abbreviated, in the higher 
Vertebrates, that no, or very little, trace of many of the 
most important phylogenetic features are retained in the 
Ontogeny. Such explanation as is afforded by the latter 
would be entirely useless to us if Comparative Anatomy 
did not lend its aid, and afford us the clearest guidance in 
our search for tribal history. 

Comparative Anatomy is, therefore, especially important 
in helping us to understand the vascular system, and, 
equally, the skeleton system, so that, without its guidance, 
it is unsafe to take a single step in this difiicult field. 
Positive proof of this assertion can be gained by studying 
the complex vascular system as explained in the classical 
works of Johannes Miiller, Heinrich Eathke, and Karl 
Gegenbaur. An equally strong negative proof of the asser- 
tion is afforded by the ontogenetic works of Wilhelm His, 
an embryologist of Leipsic, who has no conception of Com- 
parative Anatomy, nor consequently, of Phylcgeny. In 
1868, this industrious but uncritical worker published cer- 
tain comprehensive " Studies of the First Rudiment of the 
Vertebrate Body," which are among the most wonderful 
productions in the entire literature of Ontogeny. As the 
author hopes to attain a " mechanical " theory of develop- 
ment by means of a most minute description of the germ- 
history of the Chick alone, without the slightest reference 
to Comparative Anatomy and Phylogeny, he falls into 
errors which are unparalleled in the whole literature of 
56 



353 THE EVOLUTION OF MAN. 

Biology, rich as this unfortunately is in errors. Only in the 
magnificent germ-history of the Bombinator by Alexander 
Goette is incomprehensible nonsense and derision of every 
reasonable causal connection in evolution more nakedly set 
fortL (Cf. vol. i. pp. 65, 66.) His announces, as the final 
result of his investigations, " that a comparatively simple 
law of growth is the only essential in the first process of 
evolution. All formation, whether it consist in fission of 
layers, or in the formation of folds, or in complete articula- 
tion, results from this fundamental law." Unfortunately 
the author does not say in what this all-embracing " law of 
growth" really consists; just like other opponents of the 
theory of descent who substitute a great " law of evolution," 
without telling anything of its nature. From the study of 
the ontogenetic works of His, on the otl er hand, it soon 
becomes evident that he conceives form-constructing 
" Mother Nature " merely as a kind of clever dressmaker ; 
by cutting out the germ-layers in various ways, by bend- 
ing, folding, pulling, and splitting them, this clever semp- 
stress easily brings into existence the various forms of 
animal species, by " development " (!). The bendings and 
foldings especially play the most important part. Not only 
the differentiation of head and trunk, of right and left, of 
central stem and periphery, but also the rudiment of the 
limbs, as also the articulation of the brain, the sense-organs, 
the primitive vertebral column, the heart, and the earliest 
intestines, can be shown, with convincing necessity (!) to be 
mechanical results of the first development of folds. Most 
grotesque is the mode in which the dressmaker proceeds in 
forming the two pairs of limbs. Their first form is deter- 
mined by the crossing of four folds bordering the body, 



HIS OM THE VASCULAR SYSTEM. 353 

"like the four comers of a letter." Yet this wonderful 
" envelope theory " of the vertebrate limbs is surpassed by 
the " waste-rag theory " (Hollen-lappen Theorie) which His 
gives of the origin of the rudimentary organs : " Organs 
(like the hypophysis and the thyroid gland) to which no 
physiological part has yet been assigned, are embryonic 
remnants, comparable to the clippings, which in the cutting 
of a dress cannot be entirely avoided, even by the most 
economical use of the material " (!). Nature, therefore, in 
cutting out, throws the superfluous rags of tissue into the 
waste heap. Had our skull-less ancestors of the Silurian 
age had any presentiment of such aberrations of intellect 
of their too speculative human descendants, they would 
certainly have preferred relinquishing possession of the 
hypobranchial groove on the gill-body, instead of trans- 
mitting it to the extant Amphioxus, and of leaving a 
remnant of it to us, in the equally unsightly as useless 
thyroid gland. (Of p. 836). 

It will probably be thought that the ontogenetic " dis- 
coveries " of His, which appear in a doubly comical light in 
consequence of the accompanying display of mathematical 
calculations, can only have occasioned momentary amuse- 
ment in critical scientific circles. Far from it ! Immedi- 
ately after their appearance, they were not only much 
praised as the beginning of a new " mechanical " era in 
Ontogeny, but they have even yet numerous admirers and 
adherents, who ^eek to spread the scientific errors of His as 
far as possible. On this account, I have felt myself obliged 
to point out emphatically the complete falsity of these 
views. The vascular system afibrds especial occasion for 
this ; for among the most important advances which Hit 



354 THE EVOLUTION OF MAN. 

claims to have caused by his new conception of germ* 
history, is, according to him, his discovery that "the blood 
and tissue of the connective substance " (that is to say, the 
greatest part of the vascular system) *' do not originate from 
the two primary germ-layers, as do all the other organs, 
but from the elements of the white yelk." The latter 
is designated as " supplementary yelk, or parablast," to 
distinguish it from the "main-germ, or arcbiblast" (the 
germ-disc composed of the two primary germ-layers). 

The whole of this artificial development theory of His, 
and above all the unnatural distinction between the supple- 
mentary and the main germ, collapses like a card house 
when the Anatomy and Ontogeny of the Amphioxus, that 
invaluable lowest Vertebrate, is contemplated, which alone 
can elucidate the most difficult and darkest features in the 
development of the higher Vertebrates, and thus also of 
Man. The gastrula of the Amphioxus alone overthrows 
the whole artificial theory; for this gastrula teaches us 
that all the various organs and tissues of complete Verte- 
brates originally developed entirely from the two primary 
germ-layers. The developed Amphioxus, like all other 
Vertebrates, has a differentiated vascular system and 
a skeleton of " connective substance tissues " extending 
throughout its body, and yet there is in this case no " sup- 
plementary germ" from which these tissues can originate 
thus, contrasting with the other tissues. 

The larvae of the Amphioxus, arising from the original 
bell-gastrula {archigastrula), in its further development, 
throws the most important rays of light also upon the diffi- 
cult history of development of the vascular system. In the 
first place, it answers the very important question, which 



THE VASCULAB SYSTEM. 355 

we have already frequently indicated, as to the origin of 
the four secondary germ-layers ; it clearly shows that the 
skin-fibrous layer originates from the exoderm, the intes- 
tinal-fibrous layer, on the contrary, in an analogous manner, 
from the entoderm of the gastrula ; the cavity thus caused 
between the two fibrous layers is the first rudiment of the 
body-cavity, or the coelom (Figs. 50, 51, vol. i. p. 236). As the 
Amphioxus larva thus shows that the fission of the layers 
is the same in the lowest Vertebrates as in the Worms, it at 
the same time represents the phylogenetic connection be- 
tween the Worms and the higher Vertebrates. As, more- 
over, the primitive vascular stems in the Amphioxus 
originate in the intestinal wall, and in this, as in the em- 
bryos of all other Vertebrates, proceed from the intestinal- 
fibrous layer, proof is afforded us that the earlier embryolo- 
gists were right in calling the latter the vascular layer. 
Finally, the Comparative Ontogeny of the different verte- 
brate classes further convinces us that the vascular layer 
is originally everywhere the same. The vascular system in 
Man, as in all Skulled Animals, forms a complex apparatus 
of cavities, which are filled with juices, or fiuids, containing 
cells. The vessels play an important part in the nourish- 
ment of the body ; some of them conduct the nutritive 
blood fluid round in the different parts of the body (blood- 
vessels) ; some collect the wasted juices and discharge them 
from the tissues (lymph-vessels). With the latter, the 
great "serous cavities" are also connected, especially the 
body-cavity, or cceloma. The heart, acting as a centre of 
motion for the regular circulation of the juices, is a strong 
muscular pouch, which contracts in regular pulsations, and 
IS provided with valves, like those of a pump apparatus 



356 THE EVOLUTION OF MAN. 

This eonstant and regular circulation of the blood alone 
makes the complex change of substance with the higher 
animals possible. 

Important as is the vascular system in the more highly 
developed and diflferentiated animal body, it is not, however, 
an apparatus as indispensable to animal life as is generally 
supposed. In the older theory of medicine the blood was 
regarded as the real source of life, and " humoral pathology" 
referred most diseases to " corrupt blood-mixture." Simi- 
larly, the blood plays the most important part in the pre- 
vailing, obscure conception of Heredity. Just as half-blood, 
pure blood, etc., etc., are yet common phrases, so it is wideljy 
believed that the transmission, by Heredity, of definite 
morphological and physiological characters from the parent 
to the child "lies in the blood." That this customary 
notion is entirely false, is easily seen from the fact that, 
neither in the act of procreation is the blood of the parents 
directly transmitted to the procreated germ, nor does the 
embryo acquire blood at an early period. As we have 
already seen, not only the separation of the four secondary 
germ-layers, but also the beginning of the most impor- 
tant organs, takes place, in the embryos of all Vertebrates, 
before the rudiment of the vascular systems, of the heart 
and blood, is formed. In accordance with this ontogenetic 
fact, we must, from a pliylogenetic point of view, regard the 
vascular system as the most recent, the intestinal system, 
on the contrary, as the oldest formation of the animal body 
The origin of the vascular system is, at least, much later 
than that of the intestinal system. If the fundamental law 
of Biogeny is rightly appreciated, it is possible, from the 
ontogenetic sequence, in which the various organs of the 



▲GE OF THE VASCULAR SYSTEM. 357 

animal body consecutively originate in the embryo, approxi- 
mately to infer the phylogenetic sequence, in which these 
organs gradually developed, one after the other, in the 
ancestral line of animals. In the " Gastrsea theory '* I made 
the first attempt to establish the phylogenetic significance 
of the ontogenetic sequence of the organ-systems; but it 
must be remarked that this sequence is not always iden- 
tical in the higher animal tribes. In Vertebrates, and 
therefore also in our own ancestral line, the organ-systems 
may be ranged according to age, in something like the 
following order : I. The skin- system (A) and the intestinal 
system (B). II. The nerve (C) and muscular systems (D). 
III. The kidney system (^EJ). IV. The vascular system (F). 
V. The skeleton system (G). VI. The sexual system (H). 
(Cf Table XXXIX., p. 367.) 

In the first place," the gastrula proves that in all animals 
with the exception of the, Primitive Animals (Protozoa), — 
therefore, in all Intestinal Animals (Metazoa), — two primary 
organ-systems originally arose simultaneously and first; 
these were the skin-system (skin-covering) and the intes- 
tinal system (stomach-pouch). The first is represented, in 
its earliest and simplest form, by the skin-layer or exoderm, 
the latter by the intestinal layer or entoderm of the Gastraea. 
As we can ascribe the same origin, and, therefore, also the 
same morphological significance, to these two primary germ- 
layers in all Intestinal Animals, from the simplest Sponge 
to Man, the homology of these two layers seems sufficient 
proof of the above assumption. 

Immediately after the differentiation of the two primary 
germ-layers, an inner or outer skeleton develops in many 
lower animals (e.g., in Sponges, Corals, and other Plant 



358 THE EVOLUTION OF MAN. 

Animals). In the ancestors of Vertebrates, the development 
of the skeleton did not take place till much later, in the 
Chorda Animals (Ghordonia), In them, after the skin- 
system and the intestinal system, two other organ-systems 
simultaneously arise ; these are the nervous and the mus- 
cular S3^s terns. The way in which these two organ-systems 
which mutually condition each other, developed simulta- 
neously and independently, in reciprocal action and yet in 
opposition to each other, was first explained by Nicholaus 
Kleinenberg in his excellent monograph on the Hydra, the 
common fresh- water Polyp. ^^^ In this interesting little 
animal, single ceUs of the skin-layer send fibre-shaped pro- 
cesses inward, which acquire the power of contraction, the 
capacity, characteristic of the muscles, of contracting in a 
constant direction. The outer, roundish part of the exo- 
derm cell remains sensitive and acts as the nervous element, 
the inner, fibre-shaped part of the same cell becomes con- 
tractile, and, incited to contraction by the former part, acts 
as the muscular element (Fig. 293). These remarkable 
neuro-muscular cells thus still unite in a single individual 
of the first order the functions of two organ-systems. One 
step further; the inner, muscular half of the neuro-muscular 
cell (Fig. 293, m) acquires its own nucleus, and separates 
from the outer, nervous half (n), and both organ-systems 
have their independent element of form. The fission of the 
muscular skin-fibrous layer from the nervous skin-sensory 
layer in embryonic Worms confirms this important phylo- 
genetic process (Figs. 50, 51, vol. i. p. 236). 

These four organ-systems, which have been mentioned 
were already in existence, when an apparatus developed, 
tertiarily, in the human ancestral line, which, at first 



THE KIDNEYS. 359 

sight, seems of subordinate significance, but which proves, 
by its early appearance in the animal series and in the 
embryo, that it must be very ancient and, consequently, of 
great physiological and morphological value. This is the 
urinary apparatus, or kidney system, the organ-system 
which secretes and removes the useless fluids from the body 
We have already seen how soon the primitive kidneys 
appear in the embryo of all Vertebrates, long before any 
trace of the heart is discoverable. Correspondingly, we also 
find a pair of simple primitive kidney ducts (the so-called 
excretory ducts or lymphatic vessels) almost universally 
difiused in the Worm tribe, which is so rich in forms. Even 
the lowest classes of Worms, which have as yet neither 
body-cavity nor vascular system, are furnished with these 
primitive kidneys (Fig. 280, nCy p. 327). It was only in 
the fourth place, after the kidney system, that the vascular 
system developed in our invertebrate ancestors; this is 
plainly shown in the Comparative Anatomy of Worms. 
The lower Worms {Acoslomi) possess no part of the vas- 
cular system, no body-cavity, no blood, no heart, and no 
vessels ; this is the case, for example, in the comprehensive 
group of the Flat Worms (Plathelniintkes), the Gliding Worms 
(Turhellaria), the Sucking Worms {Trematoda), and the 
Tape Worms. In the higher Worms, which are therefore 
called Coelomati, a body-cavity {coeloma), filled with blood, 
first begins to form ; and, side by side with this, special 
blood-vessels then also develop. These features have been 
transmitted from the Coelomati to the four higher animal 
tribes. 

These organ-systems are common to Vertebrates and to 
the three higher animal tribes, the Articulated Animals 



$6o TETE EVOLUTION OF MAN. 

(Arthropodd), the Soft-bodied Animals -(il/o^Zitsca), and the 
Star Animals {Echinoderma), and we may, therefore, infer 
that they have all acquired these, as a common inheritance 
from the Coelomati ; but we now meet with a passive 
apparatus of movement, the skeleton system, which, in this 
form, is exclusively peculiar to Vertebrates. Only the very 
first rudiment of this, the simple notochord, is found in 
Ascidia, which are the nearest invertebrate blood-relations 
of Vertebrates. We . infer from this, that the common 
ancestors of both, the Chorda Animals, did not branch oflf 
from the Worms till a comparatively late period. The 
notochord is, it is true, one of those organs which appear at 
a very early period in the vertebrate embryo ; but this is 
clearly due to an ontogenetic heterochronism, to displace- 
ment in time in the germ-history, that is, a gradual dis- 
arrangement in the original phylogenetic sequence, caused 
by embryonic adaptation. On Comparative Anatomical 
grounds it may safely be assumed, that the first origin of 
the skeleton system did not precede, but followed that of 
the kidney system and of the vascular system, although 
Ontogeny appears to indicate the contiary. 

Last of all the organ-systems, the sexual system finally 
developed, in the sixth place, in our ancestors ; of course it 
must be understood that this was last, in the sense that the 
sexual apparatus acquired the independent form of a special 
organ-system subsequently to all the other organs. The 
simplest form, that of reproductive cells, is certainly very 
ancient Not only the lowest Worms and Plant Animals 
propagate sexually, but this was also probably the case in 
the common parent-form of all Metazoa, in the Gastraea; 
but in all these low animals, the reproductive cells do not 



AGE OF THE TISSUEa 361 

constitute special sexual organs in a morphological sense ; 
they are rather, as we shall soon see, simple component parts 
of other organs. 

Like the organ-systems of the human body, the tissues, 
which compose these systems, are of different ages and of 
vaiying morphological value. As we were justified in 
drawing an inference as to the phylogenetic sequence in 
age of the organ-systems, from the ontogenetic sequence 
in which they successively appear in the embryo, so are 
we justified in inferring the order in which the tissues 
originated during the course of tribal history, from the 
sequence of the stages in germ-history. The result of this 
is a phylogenetic classification (Table XXXVIII.) of the 
tissues of the human body, similar to that of the organs 
(Table XXXIX., p. 367). 

The tissues of the human body, arising by division of 
labour, the separation and the connection of the component 
cells, may be distributed, with reference to their develop- 
ment, in the four following distinct gi'oups : — 1, covering- 
tissue {epitheliutn) ; 2, connective tissue (connectivum); 3, 
nerve and muscular tissue (neuro-musculum) ; and 4, vas- 
cular tissue (vasalium). Of' these, in accordance with the 
Gastrsea theory, we must regard the covering-tissue as the 
oldest and most original form, as the actual primary o) 
primitive tissue ; the three other main forms must, on the 
other hand, be considered as secondary or derived forms, 
which developed at a later period from the covering-tissue ; 
the connecting-tissue first, then the neuro-muscular, and 
lastly the vascular tissue. 

The oldest and most original form of tissue is, un- 
doubtedly, the covering-tissue (epithelium), the ceUs of 



362 



THE EVOLUTION OF MAN. 



which are arranged in a simple strata-like way, and extend 
over the outer and inner surface of the body as a protective 
and secreting cover. This is proved by the simple fact that 
the formation of the tissues of the animal body begins 
with the formation of the gastrula, and that the latter 
itself consists solely of two simple epithelial strata, of the 
skin-layer (Fig. 274, e), and of the intestinal-layer (i). 
Histologically, the two primary germ-layers are simple 
epithelia. When these, afterwards, separate into the four 
secondary germ -layers, the skin-sensory layer becomes the 
outermost of the external coverings (dermal-epithelium) ; 
the intestinal-glandular layer becomes the innermost of the 
internal coverings (gastral-epithelium). The tissue of the 
outer skin and of all its appendages, such as nails (Fig. 289), 






Fig. 289. — Tissue of the nails (flattened epithelium) : a-e, cells of tha 
npper strata ; /, g, cells of the lower strata. 

Fig. 290. — Tissue of the covering of the small intestine (columnai 
epithelium) : a, side view of thi-ee cells (with thicker, porous borders) ; &, 
surface view of four cells. (After Frey.) 



hairs, skin-glands, etc., arise from the skin-sensory layer. 
(Cf. Table XXIX., p. 232.) The inner covering of the intes- 
tinal tube and of its intestinal glands originates, on the 
other hand, from the intestinal-glandular layer (Fig. 290). 



TISSUES. 3^3 

Connective tissue (connectivum) must be regarded as 
forming, in order of phylogenetic age, the second main 
group of tissues. This is morphologically characterized by 
the intercellular substance, which develops between the 




Fig. 291. — Jelly-like tissue from the vitreons body of an embryo of four 
months (round cells as jelly-like intercellular substance). 

Fig. 292. — Cartilage-tissue of the fibrous or netted cartilage of the ear- 
shell : a, cells ; h, intercellular mass ; c, fibres in the latter. (After Frey. ) 

cells, physiologically, by the double part which it plays, 
as connecting substance and as complementary substance 
between the other tissues, as an inner supporting substance 
and as a protective covering for the inner organs. Of the 
numerous forms and varieties of connective tissue, we regard 
the jelly-like tissue (Fig. 291 ; Fig. 6, vol. i. p. 126), the fatty 
tissue, and the chorda tissue as the earlier; the fibrous, 
cartilaginous (Fig. 292), and bone- tissue (Fig. 5, vol. i. p. 126) 
as the more recent formations. All these various forms of 
connective tissue are products of the middle germ-layer, 
or mesoderm ; or, more accurately, of the two fibrous layers, 
of which the skin-fibrous layer is originally derived from 
the exoderm, the intestinal-fibrous layer from the entoderm. 
The nerve-muscular tissue (neuro-musculum) is of much 
more recent origin than the connective tissue. If epithelial 
tissue represents a primary period in tribal history, and 



3^4 



THE EVOLUTION OF MAN. 



connective tissue a secondary period, then we may cha- 
racterize a third, much later period, by nerve-muscle tissue. 




Fig. 293. 





Fig. 294. 



Fig. 293. — Nerve-muscle tissue. Three cells from Hydra : w, outer, 
nervous ; m, inner, muscular part of the cells. (After Kleinenberg.\ 

Fig. 294. — Nerve-tissue (from a spinal nerve knot) : a, anterior, h^ 
posterior root of the spinal nerve ; d, e, fibrous nerve- stem ; /, g, h, i, nerve 
cells in ganglion (/, unipolar, g, h, bipolar cells) ; k, I, nerve fibres. (After 
Frey.) 

Fig. 295. — Muscle-tissue. Three pieces of striped muscle fibre (a). In= 
terfibroui: f a,t.cells (&). (After Frey.) 

For while in the lowest Plant Animals the body consists 
merely of covering tissue, and while in many other 



TISSUES. 365 

Zoophytes a middle layer of connective tissue develops 
between the two primary germ-layers, it is only in the 
most highly developed Plant Animals that muscle and nerve 
tissue is formed. As has already been said, the latter first 
appeared as a common nerve and muscle tissue {neuro- 
musculum, Fig. 293 ; cf p. 358). It was only afterwards 
that the muscle-tissue (Fig. 295) separated from the nerve- 
tissue (Fig. 294). The gi^eater part of the nerve-tissue is 
derived from the skin-sensory layer, the greater part of the 
muscle-tissue from the skin-fibrous layer. 

Vascular tissue (vasalium) must be regarded as forming 





Fig. 296. — Ta:^cnlar tissne {vasalium). A hair- vessel from the 
mesentery : a, vascular cells ; h, the kernels of these ("endothelium"). 

Fig. 297. — Eed blood cells (corpuscles) of various Vertebrates (equally 
magnified): 1, Human; 2, Camel; 3, Pigeon; 4, Proteus (p. 129); 5, Water- 
salamander {Triton) ; 6, Frog ; 7, Fish {Cohitis) ; 8, Lamprey (Petromyzon) ; 
a, surface view ; h, edge view. (After Wagner, j 



( 36e ) 

TABLE XXXYIII. 

fljlfetmatio Stirvey of the Sequence, according to Age, of the 

Tissue-groTips. 

(Phylogenetic Classification of Vertebrate Tissues.) 



FIRST GROUP: PRIMARY TISSUES (Epithelium). 

1. FntsT Histological Stage of Evolutioh. 
L Covering-tissue (Epithelium). 

I. A. Skl»^»T«ring tissue ^Epithelium cU^-male). (^ gfSs oAufrSlT"^ 

SkiB-layer. or Exodenn of Gastrula (after- ^ f^^^f s'ite^Vorigin of the f^^ 
wMdB skin-sensory layer) I cells?) » -f«»"- 

I. B. Intestinal covering tiBBue (Epithet. gastraleX (\. Real intestinal epithelium 

Intestinal layer, or Entoderm, of Gastrula •< 2. Epithelium of the intestinal glandi 
(Afterwards the intestinal-glandular layer) ( 3. (Earliest site of origin of egg-cell ?) 



SECOND GROUP: SECONDARY TISSUES. 
(All derived from the Covering-tissue, or Epithelium.) 

2. Second Histological Stage of Evolution. 
II. Connective-tissue (Connectivum). 



Jelly-like tissu* 
Fatty tissue 
Fibrous tis'^na 
Chorda tissue 



II. C. FilHng-Tip tissue (TeJa conjuiKti/va) (softer jg* 
[surrounding] connective tissue) "i ^ 

II. D. Supporting tissue {Tela skeletaris) (firmer/ J; CaitU^inous tissue 
[flupportmg] connective tissue) | g Bone-ttssue 

8. Third Histological Stage of Evolution. 



III. Nerve-muscle Tissue 



in.. 



m. 



I Kerre-tiesue (Tela 
mervea). Original outer 
portion of the nerre- 
muBcle cells of the 
Exodenn 

P. MuBcle-tissne {Tela 
mtacularis). Original 
Inner portion of the 
nerve-muscle cells of 
the Exodenn 



Nerve-cells 
(Ganglion-cells) 

Nerve-fibres 
(Nerve-tubes) 

One-celled muscle- 
fibres 

Many-celled muscle- 
fibres 



(Neuro-miksculum). 

[ 1. a. Peripheric nerve-cells (Rod-cells o! 

< the sense-organs) 

( 1. 6. Central nerve-cells (mind -cells) 

(2. a. Sheath less nerve-fibres (pale, or 
medulla-less fibres) 
2. 6. Slieathed nerve-fibres (dark fibres 
with medulla) 

1. o. Smooth contractile fibre-cella 
1 b. Striped contractile fibre-cell* 

2. a. Smooth muscle-masses 
2. h. Striped muscle-masses 



4. Fourth Histological Stage of EvoLunov. 



IV. 



Vascular Tissue (Vasalium). 



I. a. 



IT.0. Vascular lining tissue 
{Tela vasalis). Inner 
wall-covering of the 
OoBlom system 



fW.K. I^rmph-tissue {Tela ( 
lymphatiea'). Liquid 1 1. 
eentents of tlM C<elom 1 2. 



Ccelarium 

(Ccelom 

lium) 



epithe-^j b. 



Endothelium f 

(Vascular epitbe- < 

Uum) ( 



Exocoelarium (Parietal Ocelom-epl- 
thelium) (and secondary site oi 
origin of the sperm-cells H) 

Endocoelarium (Visceral coelom-eirf- 
thelium) (and secondary site of 
origin of the egg-cells })* 

Endothelium of the lymph-vessels 
Endothelium of the blood-vessels 



') 






Lymph (Colourless blood-cells and fiuid intercellular 
Blood (Red blood-cells and fluid intercellular substeaee) 



( 367 ) 
TABLE XXXIX. 

8y B tem atio Snrvey of the Sequence, according to Age, of the Hi 

Organ-systems. 

(Phylogenetic Classification of Vertebrate Organs.) 
(On the right are given the Ancestral Stages, 'n which the respective 
organs probably first appeared.) 

1. FiBST Stage in the ETOLrrroy of Ohgajti. 

I. Skin and Intestinal Systems. 

Tbe two Systems appear first, and simultaneously, in the Oaatread aaeetton. 

I A 1. Simple exoderm (Hstreafdi 

A 2. Outer skin (Skin-sensory layer) and ) Worms 
leather skin (Skin-fibrous layer) j 
A 3. Outer skin, with hairs, glands, etc. Mammals 

!£ 1. Simple entoderm Gastneads 

B 2. Intestinal epithelium (Intestlnal-glan- '\ 
dular layer) and intestinal muscular \ WorBis 
skin (Intestinal-fibrous layer) ) 

B 3. Gill-intestine and stomach -intestine Ghorda-anim*lB 



S. Second Stage is the Evolution op Obqamb. 
II. Nerve and Muscle Systems. 
Tke two Sjitems appear first, and simultaneously, in the PrimitiT* Warm aooestors. 

n r Nprve svstem I ^ ^- ^PP^"" ^^^^^^ S-nglia Primitive Worms 

11. U. jNerve-sysiem ^2. Simple medullary tube Chorda-animals 

iSystema nervtam) ( ^ 3 3,.^/^ ^^^ spinal marrow Monorhina 

TT n M«o,,i» Q,To*a»« lD\. Skin-muscle pouch Primitive Worms 

"^w™ SvJ«r-^ \ ^ 2- Side muscles of the trunk Acrania 

iSyitaaa mtocotore) | ^ 3 ^^^^j^ ^^ ^^^ muscles Fishes 

8. Third Stage in the Evolution of Oboajm^ 

III. Kidney and Vascular Systems. 

TW tw« Systems first appear, one after the other. In the Soft-wona ABoeskon (JSKUcida). 

1^1. Primitive kidney canAli Scolecida 

^2. Segmental canals Acrania? 

^3. Primitive kidneys Monorhina 

E4,. Permanent kidneys Ptotamnia 

ri^l. Simple coelom Scolecida 

OL F. Vascular system \ F2. Dorsal and ventral vessel* Worms 

{Syitema vatculare) j /«' 3. Heart (part of the ventral vewel) Chorda-animals 

I J? 4. Heart, with auricle and ventricle Monorhina 

4. FouBTH Stage in the Evolution of Osgani. 

rV. Skeleton and Sexual Systems. 

Tbe two Systems first appear, one after tbe other, in the Cliordonia-anceston. 

/-(? 1. Simple notochord Chorda-animals 

IV. O. ^eleton-system J G 2. Cartilaginous primitive ikoU Monorhina 

{SysteiMk $ktUtare) J (? 3. Gill-arches, ribs, limbs Selachii 

V. 6^ 4. Limbs, with five digits Amphibia 

{^1. Simple hermaphrodite glands Chorda-animala 

H2. Distinct testes and ovaries Acrania 

JI3. Seed-duct and oviduct Selachii 

^4. Phallus (penis, clitoris) Piotamnia 

57 



36S THB EYOLUnON OF MAX. 

the most recent group of tissues, that which originated last 
Under this name are included those epithelial-like tissues 
which line the closed inner cavities of the body (the coelom, 
chest-cavity, ventral cavity, heart-cavity, blood-vessels, etc. 
(Fig. 296). In addition to this vascular carpet (endo- 
thelium), the liquids containing cells, which fill these 
cavities (lymph, blood, serum, etc.), must be classed with 
this tissue (Fig. 297). All these tissues may be grouped as 
vasalia. His wrongly ascribed to them a quite different, 
" parablastic " origin (from the nutritive yelk) ; they are, 
however, products of the intestinal-fibrous layer (and partly, 
perhaps, of the skin-fibrous layer). As the coeloma and the 
whole vascular system is of more recent phylogenetic origin, 
its peculiar tissues must also be more recent. 

This phylogenetic explanation of the ontogenetic suc- 
cession of the tissues and of the organ systems arising from 
them, appears to me to be satisfactorily proved by Com- 
parative Anatomy, and by the Gastrsea theory. If it is 
correct, it discloses an interesting glimpse into the entirely 
various age of the most important constituent parts of our 
body. The human skin and intestine are, according to this, 
many thousands of years older than the muscles and nerves; 
these again are much more ancient than kidneys and blood- 
vessels, and the latter, finally, are many thousands of years 
older than the skeleton and the sexual organs. The com- 
mon view, that the vascular system is one of the most 
important and original organ-systems, is, therefore, erro- 
neous ; it is as false as the assumption of Aristotle that 
the heart is the first part to form in the incubated chick. 
On the contrary, all lower Intestinal Animals show plainly 
that the historic evolution of the vascular system did not 



BUDIMENTABY VASCULAR SYSTEM. 369 

begin till a comparatively late period. Not only ail Plant 
Animals (Sponges, Corals, Hydropolyps, Medusae), but also 
all lower Worms {Aco&lorai), are entirely destitute of 
vascular system. In both groups, the fluid acquired by 
digestion Ie conveyed directly from the intestinal tube, 
through processes of this latter (the gastro-canals), into the 
different parts of the body. It is only in the intermediate 
and higher Worms that the vascular system first begins to 
develop, in consequence of the formation of a simple cavity 
(c€eloina)f or of a system of connected spaces, round the 
intestinal tube, in which cavities the nutritive fluid (blood) 
exuded through the intestinal wall, collects. 

In the human ancestral line we meet with this first 
rudiment of the vascular system in that group of Worms 
which we spoke of as Soft Worms (Scolecida; p. 86). 
The Soft Worms, as we said, formed a series of intermediate 
stages between the lowest bloodless Primitive Worms 
(Archelminthes) and the Chorda- worms (C%ordonia), which 
are already provided with a vascular system and a noto- 
chord. The vascular system must have begun, in the older 
Scolecida, with a very simple coelom, a "body-cavity," 
filled with blood, and which surrounded the intestinal tube. 
Its origin was probably due to the accumulation of 
nutritive fluid in a cleft between the intestinal-fibrous 
layer and the skin-fibrous layer. A vascular system in 
this simplest form is yet found in the Moss-poljrps (Bryozoa) 
m the Wheel-animalcule {Rotatoria), and in other lower 
Worms. The inner, visceral, part of the wall of the coelom 
is, naturally, formed by the intestinal-fibrous layer (endo- 
oodar), the outer, parietal, part by the skin-fibrous layer 
(eococwlar), "Jlje po^lom fluid, collected between the two, 



370 THE ICVOLUTION OP MAN. 

may contain detached cells (lymph-cells) from either fibrous 
layer. 

A first advance in the development of this most primi- 
tive vascular system was accomplished by the formation of 
canals or blood-conducting tubes, which developed, inde- 
pendently of the coeloma, in the intestinal wall, that is, in 
the intestinal-fibrous layer of the wall. These real blood- 
vessels, in the stricter sense, appear in very different 
form in Worms of the intermediate and higher groups ; 
sometimes they are very simple, sometimes very complex. 
Two primordial " primitive vessels " must be regarded as 
representing that form, which probably formed the first of 
the more complex vascular system of Vertebrates ; these are 
a dorsal vessel, which passes from front to back along the 
middle line of the dorsal wall of the intestine, and a ventral 
vessel which passes, in the same direction, along the middle 
line of the ventral wall Both at the front and at the 
back these two vessels are linked together by a loop sur- 
rounding the intestines. The blood enclosed in the two 
tubes is driven forward by the peristaltic contraction of 
this. 

The further development of this simplest rudimentary 
blood-vessel system is evident in the class of the Ringed 
Worms (Annelida), in which we find it in very variorw 
stages of development. In the first place, many trans- 
verse connections probably arose between the dorsal and 
ventral vessels, so as to encircle the intestine (Fig. 298), 
Other vessels then penetrated into the body-waU and 
branched, so as to conduct blood to this part. As in those 
ancestral Worms, which we have called Chordoma, the 
front section of the intestine changed into a gill-body, theM 



THE VASCULAR SYSTEM. 



371 



t 



\ 



asculai- loops, within the wall of this gill-body, which 
passed from the ventral vessel to the dorsal vessel, became 
modified into respiratory gill- vessels. Even at the present 
day, the organization of the remarkable Acorn-worm 
(Balanoglossiis) exhibits a similar condition of gill-circula- 
tion (Fig. 186, p. 86). 

A further important advance is exhibited, 
among extant Worms, in the Ascidia, which 
must be regarded as the nearest blood-rela- 
tions to our primitive Chordonia ancestors. 
In these we find, for the first time, a real 
heart, that is, a central organ of the circula- 
tion of the blood, by the pulsating contractions . 
of the muscular wall of which the blood is 
driven forward in, the vascular tubes. The 
heart appears here in the simplest ^'form, as 
a spindle-shaped pouch which passes at both 
ends into a main vessel (Fig. 188, c. p. 90; 
Plate XI. Fig. 14, hz). The original position 

Fig. 298. — Blood-vessel system of a Einged Worm 

(Saenuris) ; front section : d, dorsal vessel ; v, ventral 

vessel ; c, transverse connection between the two (en- 

larged like a heart). The arrows indicate the direction ot 

li- 
the blood current. (After Gegenbaur.) * 

of the heart on the ventral side, behind the gill-body of the 
Ascidian, plainly shows that it originated in a local dilation 
of a section of the ventral vessel. The alternatinof direc- 
tion of the movements of the blood, which has already been 
mentioned, is remarkable ; the heart expels the blood alter- 
nately through the anterior and through the posterior end. 
This is very suggestive, because in most Worms the blood 



^ « 



372 THE EVOLUTION OF MAN. 

in the dorsal vessel moves from back to front, while in 
Vertebrates, on the contrary, it flows in the opposite direc- 
tion, from front to back. As the heart of the Ascidian 
constantly alternates between these two opposite directions, 
it exhibits permanently, to a certain extent, the phylogenetic 
transition between the older direction of the dorsal blood- 
current toward the front in Worms, and the newer direc- 
tion of the same toward the rear in Vertebrates. 

Ah in the more recent Chorda Animals, which gave 
rise to the Vertebrate tribe, the newer direction became 
permanent, the two vessels which proceeded from the 
two ends of the heart-pouch, acquired a constant signifi- 
cance. The front section of the ventral vessel, since then, 
has steadily conducted the blood from the heart, acting, 
consequently, as an artery; the hinder section of the 
ventral vessel, on the contrary, leads the blood, circulating 
in the body, back into the heart, and must, therefore, be 
called a vein. In reference to their relation to the two 
sections of the intestine, we may speak of the latter, more 
accurately, as the intestinal vein, and of the former as the 
gill-artery. The blood contained in both vessels, which 
alone fills the heart also, is venous blood ; that is, containing 
much carbonic acid. On the other hand, the blood which 
flows from the gills into the dorsal vessel is there re- 
furnished with oxygen ; is arterial blood. The most delicate 
branches of the arteries and veins pass into each other, 
within the tissue, through a network of extremely fine 
neutral hair-vessels or capillaries (Fig. 296). 

If we now turn from the Ascidia to the nearest allied 
form, the Amphioxus, we are immediately surprised by an 
apparent retrogi'ession in the development of the vascular 



DEVELOPMENT OF THE VASCULAR SYSTEM. 373 

gystem. The Amphioxus, as has been stated, haa no real 
heart ; but the blood is circulated in its vascular system by 
the main vascular stems themselves, which contract and 
pulsate along their whole length, (Of. Fig. 151, vol i. p. 420.) 
A dorsal vessel (aorta), situated over the intestine, absorbs 
the arterial blood from the gills and propels it through the 
body. The venous blood, in its return, collects in a ventral 
vessel (intestinal vein), situated under the intestine, and 
thus returns to the gills. Numerous vascular giU-arches, 
which accomplish respiration, and absorb oxygen fix)m the 
water and emit carbonic acid, unite the ventral vessel 
with the dorsal vessel before. As, in Ascidia, that section 
of the ventral vessel which also forms the heart in SkuUed 
Animals (Craniota), is already fully developed into a simple 
heart-pouch, we must regard the absence of the latter in the 
Amphioxus as the result of retrogression, as a reversion, in 
these Acrania, to the older form of vascular system, as it 
exists in Scolecida and many other Worms. We may 
assume that those Acrania which actually formed part of 
our ancestral line did not share this relapse, but rather 
inherited the one-chambered heart from the Chordoma and 
transmitted it directly to the older SkuUed Animals 
(Craniota). 

The Comparative Anatomy of Skulled Animals clearly 
exhibits the further phylogenetic development of the blood- 
vessel system In the lowest stage of this group, in the 
Cyclostoma (p. 102), we first meet with a real lymph-vessel 
system, side by side with the blood-vessel system, a system 
of canals which collect the colourless fluid, flowing from the 
tissues, and conduct it to the blood-current. Those lymph- 
vessels which absorb the milky, nutritive fluid, obtained 



374 THE EVOLUTION OF MAN. 

directly by digestion, from the intestinal wall, and conduct 
it to the blood-current, are distinguishable as chyle-vessels, 
or "milky juice vessels." While the chyle, or milky juice, 
in consequence of the great amount of fat globules which 
it contains, appears milk white, the real lymph is colour- 
less. The chyle, as well as the lymph, contain the same 
colourless amoeboid cells (Fig. 9, vol. i. p. 132), which are also 
distributed in the blood as colourless blood-cells (corpuscles) ; 
the latter contains, in addition, the much greater quantity 
of red blood-cells (corpuscles), which gives the blood of 
Skulled Animals its red colour. The distinction, common to 
aU Craniota, between lymph-vessels, chyle-vessels, and 
blood-vessels, is to be regarded as the result of a division of 
labour which took place between difterent portions of an 
original unitary, primitive blood-vessel system (or haemo- 
lymph system). . 

The heart, the central organ of the circulation of the 
blood, which exists in all Craniota, also exhibits an advance 
in structure, even in the Cyclostoma. The simple spindle- 
shaped heart-pouch is separated into two divisions, or 
chambers, which are divided by two valves (Plate XI. 
Fig. 16, hv, hk). The posterior division, the fore chamber 
(atriv/m, hv), absorbs the venous blood from the veins of 
the body, and discharges it into the anterior division, the 
chamber, or main chamber (ventriculus, hk). From here it 
is propelled by the gilJ -artery stem (the foremost section of 
the ventral vessel) into the gills. 

In Primitive Fishes {Selachii), an arterial stalk (huUms 
arteriosus), sepaiated by valves, originates, as a distinct 
section, from the foremost end of the ventricle. It forma 
the enlarged, hindmost end of the gill-artery stem (Fi^ 



DEVELOPMENT OF THE VASCULAR SYSTEM. 



375 



299, ahr). From each side of this, from five to seven gill- 
arteries proceed; these rise between the gill-openings (s) 
to the gill-arches, encircle the throat, and combine above 
into a common aorta-stem, the continuation of which, 
passing backward above the intestine, corresponds to the 
dorsal vessel of Worms. As the arched arteries distribute 
themselves in a respiratory capillary net over the gill- 
arches, they thus contain venous blood in their lower part 
(as arterial gill-arches), and arterial blood in their upper 
part (as aorta-arches). The points at which separate aorta- 
arches unite, which occur on the right and left sides, are / 
called aorta-roots. Of an originally greater number of 
aorta-arches, only five pairs are retained, and from these 
five (Fig. 300), in all higher Vertebrates, the most im- 
portant parts of the arterial system develop. 




Fig. 299. — Head of an. embryonic Fish, with the mdiment and the 
blood-vessel system ; seen from the left side : dc, Cuverian duct (point of 
anion of the front and hind main veins) ; av, venons Binns (enlarged 
terminal portion of the Cuverian duct) j a, auricle ; v, main chamber ; 
ahr, gill-artery stem; s, gill-openings (between the arterial arches); ad, 
aorta; e', head-artery (carotis) ; n, nose-groove. (After Gegenbaur.) 

The appearance of the lungs, connected with the respi- 
ration of air, which first occurs in the Dipneusta, is most 
important in the further developement of the arterial 



3/6 THE EVOLUTION OF MA«. 

system. In Dipneusta, the auricle of the heart separatefl 

into two halves by the formation of an incomplete partition. 
Only the right auricle now absorbs the venous blood of the 
body-veins. The left auricle, on the other hand, absorbs 
the arterial blood of the lung-veins ; both auricles dis- 
charge in common into the simple ventricle, in which the 
two kinds of blood mingle, and are then propelled through 
the arterial stalk into the arterial arches. From the last of 
these latter spring the lung-arteries (Fig. 301, p)) these 
convey a part of the mixed blood into the lungs, while the 
remainder is driven through the aorta into the body. 

From the Dipneusta upward, we trace a progressive 
development of the vascular system, which finally leads, 
with the loss of gill respiration, to a complete separation of 
the two parts of the double circulatory system. In Am- 
phibia, the partition between the two auricles becomes 
complete. In their young form, these yet retain gill- 
respiration and the circulatory system as in Fishes, and the 
heart contains only venous blood; at a later period, the 
lungs, with their vessels, are developed also, and the main 
chamber of the heart then contains mixed blood In Pro- 
tamnia and Reptiles, the main chamber and the arterial 
stalk belonging to it begin to separate, by the formation of 
a longitudinal partition, into two halves,, and this partition 
becomes complete in the higher reptiles on the one side, in 
the parent-form of Mammals on the other. The right half 
of the heart alone now contains venous blood, the left half 
only arterial, as in all Birds and Mammals. The right 
auricle receives venous blood from the body-veins, and the 
right ventricle propels this through the lung-arteries into 
the lungs ; from there it returns as arterial blood through 



DOUBLE CIRCULATORY SYSTEM. 



377 



the lung- veins to the left auricle, and is driven through the 
left ventricle into the body-arteries. Between t!.o lung- 
arteries and lung-veins is situated the capillary system of 
the lesser, or lung-circulation ; between the body -arteries 
and the body-veins lies the capillary system of the greater, 
ui- body-circulation. Only in the two highest Vertebrate 




Fig. 300.— The five arterial arcbes of Skulled Animals (1-5) in their 
original form : a, arterial stalk ; a", main stem of the aorta ; c, head- 
artery (carotis, anterior continuation of the aorta-roots). (After Rathke.) 

Fig. 301 — The five arterial arches of Birds; the light portions of the 
rudiment disappear ; only the dark parts are permanent. Letters as in 
Fig. 300 : s, arteries of the clavicula (sub-clavian) ; p, lung-artery ; p', 
branches of the same. (After Eathke.) 

Fig. 302. — The five arterial arches of Mammals. Letters as in Fig. 301 : 
V, vertebra] artery ; h, Botalli's duct (open in the embryo, afterwards 
closed). (After Rathke.) 

classes, in Birds and Mammals, is this complete separation 
of the two courses of the circulation perfect. Moreover, this 
separation has taken place in the two classes independently 
of each other, as is shown by the unequal development of 
the aortas. In Birds, which are descended from Reptiles, 



17^ 



THE ^VOLUTION OF MAJN. 



the right half of the fourth arterial arch has become the 
periuanent arterial arch {ar<M8 aortcB, Fig. 301). On the 
other hand, the latter has developed from the left half of 
the same arch (Fig. 302) in Mammals, which are directly 
descended from the Protamnia. 

On comparing the arterial system in the various classes 
of the Skulled Animals {Craniota) in its matured condition, 
it appears in very various forms, and yet it develops, in 
all, from the same primitive form. This development takes 
place in man exactly as in other Mammals ; especially is the 
modification of the five arterial arches precisely the same in 
both cases (Figs. 303-306). At first, only a single pair of 





Figs. 303-306. — Metamorphosis of the five arterial arches in the human 
embryo (diagi-am after Rathke) : ta, axterial stalk ; 1, 2, 3, 4, 5, the arterial 
arches from the first to the fifth pair; ad, main stem of the aorta; ate, 
roots of the aorta. In Fig. 303, three of the arterial arches are given ; in Fig. 
304, the whole five (those indicated by dots are not yet developed) ; iii Fig. 305, 
the first two have again disappeared ; in Fig. 306, the permanent arterial 
stems axe represented. The dotted parts disappear, s, Sub.clavian artery ; 
r, vertebral artery ; aa?, axillary artery ; c, carotid artery (c', outer, e", 
tnner carotis) ; j9, pulmonary artery (lung-artery) . 



arches develop, and these lie on the inner surface of the 
first pair of gill-arches (Figs. 147-150, vol. i. pp. 895-398; 
Fig. 303). A second and a third pair of arches then develop 



DEVELOPMENT OF THE HEABT. 379 

behind the first, and these are situated on the inner surface 
of the second and third gill-arches. At length, a fourth and 
a fifth pair appear behind the third (Fig. 304) ; but while 
the latter are developing, the first two are again disappear- 
ing t)y growing together (Fig. 305). The permanent main 
arteries develop only fi'om the three posterior arterial 
arches (3, 4, 5, in Fig. 304), the lung-arteries from the last 
(p ; Fig. 306). (Of. with this Fig. 802.) 

The human heart also (Fig. 314) develops exactly like that 
3f other Mammals. We have already considered the first prin- 
ciples of its germ-history (vol. i. pp. 392-395, Figs. 143-147), 
which essentially corresponds with its Phylogeny.^®^ We saw 
that the very first rudiment of the heart is a spindle-shaped 
thickening of the intestinal-fibrous layer in the ventral wall 
of the head-intestine (Fig. 143, df). This spindle-shaped 
formation then becomes hollow, forms a simple pouch, and 
separates from the place at which it originated, so that it 
then lies freely in the cardiac cavity (Figs. 145, 146). This 
pouch bends into the form of an S (Fig. 144, c), and, at the 
same time, turns spirally on an imaginary axis, so that the 
posterior part Kes on the dorsal surface of the anterior 
part. The combined yelk-veins open into its posterior 
extremity ; from the anterior extremity proceed the arterial 
arches (Fig. 150, voL i. p. 398). 

This first rudiment of the human heart, which encloses 
a very simple cavity, corresponds to the heart of the As- 
cidians, and must be regarded as a reproduction of the heart 
of the Chordoma ; it now, however, separates into two, and 
then three parts, thus exhibiting for a very brief period the 
heart-structure of the Cyclostoma and of Fishes. The spiral 
turn and curve of the heart increases, and, simultaneouslyi 



38o 



THE EVOLUTION OF MAN, 



two shallow transverse indentations of the circumference 
appear, which externally mark the three sections (Figs. 307, 
308). The anterior section, which is turned toward the 




—e r 



th'- 





Pig. 307. — Heart of an embryonic Rabbit, from behind : a, yelt-veins ; 
b, auriculae ; c, auricle (atrium) ; d, ventricle ; e, artery-stalk ; /, base of the 
three pairs of arterial arches. (After Bischoff.) 

Fig. 308. — Heart of the same embryo (Fig. 307), from the front: v, 
yelk-veins ; a, auricle ; ca, auricular canal ; I, left ventricle ; r, right 
ventricle ; ta, artery-stalk. (After Bischoff.) 

Fig. 309. — Heart and head of an embryonic Dog, from the front : 
a, fore-brain ; h, eyes ; c, mid-brain ; d, primitive lower jaw ; e, primitive 
upper Jaw ; /, gill-arches ; g, right auricle ; h, left auricle ; i, left ventricle ; 
k, right ventricle. (After Bischoff.) 

Fig. 310. — Heart of the same embryo, from behind : a, entrance of the 
yelk-veins ; h, left auricular process ; c, right auricular process ; d, auricle ; 
e, auricular canal ; /, left ventricle ; g, right ventricle ; h, artery-stalk. 
(After Bischoff.) ^ 

ventral side, and from which the aortal arches spring, 
reproduces the arterial stalk (bulbvs arteriosus) of the 
Selachii. The central section is the rudiment of a simple 
chamber, or ventricle (ventrimdus) ; and the posterior 
section, the one turned toward the dorsal side, into which 
the yelk-veins open, is the rudiment of a simple auricle 



DEVELOPMENT OF THE HEABT. 38 1 

(atrium). The latter, like the simple auricle of the heart 
of the Fish, forms a pair of lateral protuberances, the heart 
ears, or auricular appendages {av/riculcB, Fig. 307,6); and 
hence the indentation between the auricle and ventricle is 
called the auricular canal (canalia auricularis, Fig. 308, ca). 
The heart of the human embryo is now a complete Fisl 
heart 

Corresponding exactly with the Phylogeny of the human 
heart (Table XLI), its Ontogeny exhibits a gradual tran- 
sition from the Fish heart through the Amphibian heart to 
the Mammalian heart. The most important step in this 
advance is the formation of a longitudinal partition, im- 
perfect at first, afterwards complete, by which aU the three 
sections of the heart are separated into a right (venous^ and 
a left (arterial) half (Cf Figs. 309-314.) The auricle 
{atrium) is thus divided into a right and a left auricle, each 
of which acquires its respective auricular process ; the body- 
veins discharge into the right auricle (ascending and de- 
scending vena cavce, Fig. 311, c, Fig. 313, c) ; the left auricle 
receives the lung- veins. Similarly, a superficial "inter- 
ventricular furrow" (sulcus irUerventricularis, Fig. 312,8) 
appears at an early period on the main chamber of the 
heart, the external expression of the internal partition, by 
the formation of which the ventricle is divided into two 
chambers, a right (venous) and a left (arterial) ventricle. 
Finally, a longitudinal partition forms, in a similar way, 
in the third section of the primitive heart, which so much 
resembles that of a Fish, in the arterial stalk, which is also 
externally indicated by a longitudinal furrow (Fig. 312, a/). 
This separates the cavity of the artery-stalk into two 
lateral halves ; the main lung artery, which opens into the 



382 



THE EVOLUTION OF MAN. 




Fig. 311. 



Fig. 313. 



Fig. 314. 



Fig. 311. — Heart of a human embryo of four weeks ; 1, from the front ; 
2, from the back ; 3, open, and with the upper half of the amricle reuioved ; 
a', left auricular process ; a", right auricular process ; v', left ventricle ; 
v", right ventricle ; ao, artery-stalk ; c, upper hollow vein {vena cava) {cd, 
right, cs, left) ; s, rudiment of the partition, between the chambers. (After 
Koelliker.) 

Fig. 312. — Heart of a human embryo of six weeks, from the front: 
r, right ventricle ; t, left ventricle ; s, furrow between the two ventricles ; 
ta, artery-stalk ; af, furrow on its surface ; at the right and left are the 
two large auricular processes of the heart. (After Ecker.) 

Fig. 313. — Heart of a human embryo of eight weeks, from behind: 
a', left auricular process ; a", right auricular process ; v', left ventricle ; 
v", right ventricle ; cd', right upper vena cava ; cs, left upper vena cava ; 
ci, lower vena cava. (After Koelliker.) 

Fig. 314. — Heart of human adult, perfectly developed, from the front, in 
its natural position : a, right auricular process (below it, the right ventricle) ; 
b, left auricular process (below it, the left ventricle) ; C, upper vena cava ; 
V, lung -veins ; P, lung-artery ; d, Botalli's duct ; A, aorta. (After Meyer.) 

right ventricle, and the aorta-trunk, which opens into the 
left ventricle. Not until all these partitions are complete, 
is the lesser, or lung-circulation, entirely distinct from the 



POSITION OF THE RUDIMENTARY HEABT. 583 

greater, or body-circulation ; the right half of the heart is 
the centre of motion for the former, the left half for the 
latter. (Cf Table XLI.) 

In the human embryo, and in all other Amniota, the 
heart originally lies far forward on the lower side of the 
head, as in Fishes it remains permanently near the throat. 
Afterwards, with the advancing development of the neck 
and chest, the heart continually moves further back, until 
at last it is situated in the lower part of the breast between 
the lungs. At first its position is symmetrical, in the central 
plane of the body, so that its longitudinal axis corre- 
sponds with that of the body (Plate IV. Fig. 8). In most 
Mammals it retains this symmetrical position permanently ; 
but in the Apes the axis begins to incline obliquely, and to 
move the apex of the heart to the left side. This inclination 
is carried furthest in the Man-like Apes; in the Chim- 
panzee, Gorilla, and Orang, which also resemble Man in 
this oblique position of the heart. 

The germ-history of aU other parts of the vascular system, 
like that of the heart, point out many and valuable facts re- 
garding the history of our descent. But as an accurate know- 
ledge of the complex arrangement of the entire vascular system 
of Man and other Vertebrates is required, in order to follow the 
matter sufficiently far to make it intelligible, we cannot here 
enter into any further detaiL^^^ Moreover, many important 
features in the Ontogeny of the vascular system, especially 
in regard to the derivation of its various parts from the 
secondary germ-layers, are as yet very obscure and doubtful 
This is true, for example, of the question as to the origin of 
the ccelom-epithelium — that is, of the cell-layer coating the 

body-cavity. Probably there is an important phylogenetio 

58 



3^4 THE EYOLUnON OF MAK. 

distinctioii between the exocoelar, or the parietal corfom- 
epithelium, which originates from the skin-fibrous layer, and 
the endocoelar, or the visceral ccelom-epithelium, which 
ie derived fnym the intestinal-fibrous layer. The former 
is, perhaps, connected with the male germ-epithelium (the 
rudiment of the testes), the latter with the female germ- 
epithelium (the rudiment of the ovary). (Cf. Chapter XXV.) 



TABLE XL. 

ST*nM4nC SUSTIT OV THE MOST IMPOKTANT PesIODS IN THS PhTLOOSJIT 

07 THE Human Yasculae System. 

I. Fint Period : Vascular System of the earlier Seolecida. 
Between the skin-covering and the intestinal wall is formed a simple 
bodj-oavity (cesloma), or a perienteric cavitj (as in the extant Bryo»oa and 
otber Coslomati). 

IL Second Period : Veueular System of the wtore recent Seolecida. 

The first real blood-ressels form in the intestinal wall (in the intestinal* 
Abroos layer), a dorsal vessel in the central line of the dorsal side of the 
intestinal tnbe, and a ventral vessel in the central line of its ventral side. 
The two vessels are oonnected bj several oiroolar vessels, enoiroling the 
inteatixM. 

nL Third Period : VmeeuUtr System cf ike ea/rUer Chordoma. 

Bj the modification of the anterior half of the intestine into a gill- 
intestine, the anterior section of the ventral vessel becomes a gill-arterj, 
and the anterior section of the dorsal vessel a gill- vein | between the two 
a gill capillary network develops. 

rf. FovHh Period : VaseuJair System of the mare reeem t Chordoma, 

l%e portion of the ventral vessel, Ijing immediately behind the gfB>- 
te a simple beart-poook (Aaddian). 



PHTLOGENT OF THE HUMAN HEART. 385 

V. Fifth Period : Vascular System of the Acraitiim, 

The rentral vessel (intestinal vein) forms, round the deTeloping Krer- 
MO, the first rudiment of a vena portee system. 

YI. Siafth Period : Vascular System of the Cyclostomi. 

The aingle-ctambered heart divides into two chambers ; ft po8t«rior 
T©ntricle, and an anterior auricle. The lymph-ressel system derelops side 
hj side with the blood-vessel system. 

Vn. Seventh Period : Vascular System of the Prim/itive Fishes, or Selachii. 

From the anterior section of the main chamber of the heart arises an 
•riery-stalk or trunk, from which five (?) pairs of arterial arches proceed. 

Vni. Eighth Period : Vascular System of the Mud-fishes. 
From the last (fifth) pair of arterial arches the Inng-exteries develop, 
as in the Dipneusta. 

IX. Ninth Period : Vascular System of Amphihui. 

The gill-arches gradually disappear with the gills. The right and left 
aortal arches remain. 

X. Tenth Period ; Vascular System of MammmLs, 

The separation of the greater from the lesser oiroolation is complete. 
The right aortal arch unites with Botalli's duct. 



TABLE ^LL 



STimfATIC SUBVBT OF THK MOST IMPOKTANT FeEIODS IK THI PhTLOCKWT 

o? THE Human Heart. 

L First Period : Heart of Chordonia, 

The heaH forms a simple spindle-shaped enlargement of the ventral 
Teaeel, with an alternating blood-ourrent (as in Ascidia). 

II. Second Period : Heart of Acrania. 

The heart is like that of Chordonia, but the blood-current acquires 
a constant directicm, petssing only from book to front. (Betrt^raded in 
Amphioxns.) 



386 THE EVOLUTION OF MAN. 

m. Third Period : Hea/rt of Cyclostoma. 

The heart dirides into two chambers, a posterior auricle (airwm) and 
an anterior rentricle (yentricuUis). 

IV. Fowrih Period : Heart of Primitive Fishes. 
From the anterior section of the ventricle is diflferentiated an arterial 
stalk (hullm$ a/rteriosus) , as in all Selachii. 

V. Fifth Period : HeaH of the Mud-fishes. 

The auricle divides, bj an imperfect and interrupted partition, into 
a right and a left half, as in Dipneasta. 

VI. Sixth Period : Heart of Atnvhihia. 

The 'partition between the right and left auricles becomes complete, a> in 
the higher Amphibia. 

Vn. Seventh Period : Heart of Protamnia. 

The main chamber of the heart divides, by an incomplete partition, into 
a right and a left half, as in Reptiles. 

VIII. Eighth Period : Heart oj Monotrema. 

The partition between the right and left ventricles becomes completOi as 
in all Mammals. 

IX. Ninth Period : Hea/rt of Marsupials. 

The valves between the auricles and ventricles (atrio.ventricular valves), 
together with the connecting filaments and papillary muscles belonging to 
them, are differentiated from the muscular masses of Monotremes. 

X. Tenth Period : Heart of Apes. 

The main axis of the heart, lying in the central line of the bodj 
ueoomes oblique, so th&t the' apex ia turned to the left, aa in Apeft vad 



( 387 ) 

TABLE XLII. 

Sjitematic Survey of those Primitive Organs which most probably be 
regarded as homologous in Worms, Articulated Animals, Soft-bodied 
Animals, and Vertebrates.*** 



Wdms 
(Fermet). 



Articulated 

Animals 
{Arthropoda). 



Soft-bodied 
Animals 
{Molluscdy 



Vertebrates 
{rerUbrmtm). 



L Producti 


J of the Differentiation of the Skin-sensory La^er, 


1. Ooter skin 


1. Chitinous skin 


1. Outer skin 


1. Outer skin 


{Epidermis') 
1. Brain (upper throat- 


(ffypodermis^ 


{Epidermis) 
2. Brain (upper throat- 


{Epidermis) 


2. Brain (upper throat- 


3. Medullary tube (an- 


ganglia) 


ganglia) 


ganglia) 


terior part) 
S. Primitive kidney- 


3. Ebccretory organB 


3. Shell-glands of the 


3. Rudimentary kid- 


(water - vessels, 


Crustacean 


neys (Primitive 


ducts {Proture- 


segmental organs) 


(trachea of the 


kidneys) 


teres) and seg- 




Tracheata?) 




mental orgaos 



IL Products of the Differentiation of the Skin-fibrous Layer. 



1, Leather-skin 
{Corium) 

(together with the 
circular muscle- 
pouch ?) 

S. Longitudinal 
muscle-pouch 

i. Exocoelar innermost 
cell- layer of the 
body-wall (also 
Bale germ-plate?) 



4. Leather-skin 
(Rudiment) 



6. Trunk-musclea 

6. Exocoelar innermost 
cell-layer of the 
body- wall (also 
male germ-plate?) I 



4. Leather-skin 

(Corium) 

(together with the 

muscles of the 

skin ?) 
6. Inner trunk-muscles 

6. Exocoelar parietal 
epithelium of the 
coelom (also male 
germ-plate?) 



4. Leather-skln 

(Cbrium) 
(together with the 
muscular layer of 
the skin ?) 
6. Side tmnk-muscles 

6. Exoccelar parietal 
epithelium of the 
coelom (also male 
germ-plate ?) 



m. Products of the Differentiation of the Intestinal-fibrous Laymr. 



T. Body-cavity 


7. Body-cavity 


1. Body-cavity 


7. Pleuro-perttoDeal 


{Coeloma) 


{Cceloma) 


{Coelomd) 


cavity 


•l Endocoelar outer- 


8. Eiidoccelar outer- 


8. lidocflelar visceral 


8. Kndocoelar visceral 


most cell-layer 


most cell-layer 


epithelium of the 


epithelium of the 


of the intestinal 


of the intestinal 


coelom (together 


coelom (together 


wall (together 


wall (together 


with the female 


with the female 


with the female 


with the female 


germ-plate ?) 


germ-plate ?) 


germ-plate ?) 


germ-plate ?) 






•. Dorsal vessel 


9. Heart 


9. Chamber of the 
heart (and main 
artery) 




!«. Ventral vesael 


10. 


10. 


10. Heart (and gUl- 

artery) 

11. Intestinal wall (ex- 


1 L Intestinal wall (ex- 


11. Intestinal wall (ex- 
cept the epithe- 


11. Intestinal wall (ex- 


cept the epithe- 


cept the epithe- 


cept the epith^ 


lium) 


Uum) 


Uum) 


lium) 



IV. Products of the Differentiation of the Intestinal-glam^dular Layer. 



12. Intestinal epithe 
lioffi 



12. Intestinal epithe- 
liom 



12. Intestinal epithe- 
lium 



12. Intestinal 
Uun 



CHAPTER XXV. 

DEVELOPMENT OF THE URINARY AND SEXUAL ORGANS. 

Importance of Reproduction. — Growth. — Simplest Forms of Asexnal Repro- 
duction : Division and the Formation of Buds (Gemmation) . — Simplest 
Forms of Sexual Reproduction : Amalgamation of Two Differentiated 
Cells ; the Male Sperm-cell and the Female Egg-cell. — Fertilization. — 
Source of Love. — Original Hermaphroditism ; Later Separation of the 
Sexes (Gonoohorism). — Original Development of the Two Elinds of 
Sexual Cells from the Two Primary Germ-layers. — The Male Exoderm 
and Female Entoderm. — Development of the Testes and Ovaries. — 
Passage of the Sexual Cells into the Ccelom. — Hermaphrodite Rudiment 
of the Embryonic Epithelium, or Sexual Plate. — Channels of Exit, or 
Sexual Ducts. — Egg-duct and Seed-duct. — Development of these irom 
the Primitive Kidney Ducts. — Excretory Organs of Worms. — *' Coiled 
Canals " of Ringed Worms (Annelida). — Side Canals of the AmpKiowus. 
— Primitive Kidneys of the Myxinoides. — Primitive Kidneys of Skulled 
Animals (Craniotd), — Development of the Permanent Secondary 
Kidneys in Amniota. — Development of the Urinary Bladder from the 
AUantois. — Differentiation of the Primary and Secondary Primitive 
Kidney Ducts. — The Miillerian Duct (Egg-duct) and the Wolflian Dnot 
(Seed-duct). — Change of Position of the Germ-glands in Mammals. — 
Formation of the Egg in Mammals (Graafian Follicle). — Origin of the 
External Sexual Organs. — Formation of the Cloaca. — Hermaphroditism 
in Mjuu 

** The most important truths in Natural Science are discovered, neither 
by the mere analysis of philosophical ideas, nor by simple experience, bal 
by rffiectiw€ •mperitn^ which distinguishes the essential from the accidental 



IMPORTANCE OF THE RKPRODTJCIIVE STSTKIC 389 

in the phenomea* obeerred, and thiu finds principles from wUch mtaij 
experiences can be derived. This is more than mere experience ; it is, 
■o to speak, philosophical experience." — Johajjnes Mullbr (1840). 

If we judge of the importance of the organ-systems of the 
animal body according to the number and variety of 
phenomena which they present, and according to the 
physiological interest connected with them, we must recog- 
nize as one of the most important and interesting organic 
systems, the one to the development of which we now, 
finally, turn ; the system of the reproductive organs. Just 
as nutrition is the first and most important condition of 
self-preservation of the organic individual, so by repro- 
duction alone is the preservation of the kind or species 
effected, or, rather, the preservation of the long series of 
generations, which in their genealogical connection form the 
sum of the organic tribe, or phylum. No organic individual 
enjoys an eternal life. To each is granted but a short 
span of time for his individual evolution, a brief, fleeting 
moment in the long millions of years of the earth's organic 
history. 

Reproduction in connection with Heredity has, there- 
fore, long been regarded as, after nutrition, the most 
important fundamental function of the organism, and it is 
customary to make this a primary distinction between 
living bodies and lifeless or inorganic bodies. But this 
distinction is in reality not so deep and thorough as it at 
first appears, and as is generally assumed. For, if the 
nature of the phenomena of reproduction is closely con- 
sidered, it is soon seen that it may be reduced to a more 
general quality, that of growth, which belongs to inorganic, 
sm well as to organic bodies. Reproduction is a nutrition 



390 THE EVOLUTION OF MAN. 

and a growth of the organism beyond the individual size, 
which, therefore, raises a part of the organism to the rank 
of a whole (vol. i. p. 159). This is most clearly seen by 
observing the reproduction of the simplest and lowest 
organisms, especially of the Monera (p. 46) and of the one- 
celled Amoeba (p. 48). In these, the simple individual pos- 
sesses only the form-value of a single plastid. As soon as, 
by continued nutrition and simple growth, this has reached 
a certain size, it does not exceed that size, but falls, by 
simple. division, into two similar halves. Each of these 
two halves thenceforth leads an independent life, and again 
grows, till, having reached the same limit of growth, it once 
more divides. At each of these simple self-divisions, two 
new central points of attraction for the particles of the 
body are formed, as foundations of the two new indi- 
viduals.^ 

In many other Primitive Animals {Protozoa)^ the simple 
reproduction is accomplished, not by division, but by the 
formation of buds (gemmation). In this case, the growth, 
which prepares the way for reproduction, is not total (as in 
the case of division), but partial. Hence in the case of 
gemmation, the product of local growth, which, as a bud, 
forms a new individual, can be distinguished, as a young 
individual, from the parent-organism from which it 
originates. The latter is older and larger than the former. 
In the case of division, on the contrary, the two products 
are of equal age and of equal form-value. Further 
differentiated forms of asexual reproduction, connected 
with gemmation, are, thirdly, the formation of germ-buds, 
and, fourthly, the formation of germ-cells. The latter, 
however, brings us directly to sexual reproduction, for which 



BUDIMENTARY REPRODUCTIVE SYSTEM. 39 1 

the opposed differentiation of the two sexes is the condition. 
In my Generelle Morphologic (vol. ii. pp. 32-71), and in 
my " Natural History of Creation " (vol. i p. 183), I 
have fully discussed the connection of these various forms 
of reproduction. 

None of the earliest ancestors of Man and of the higher 
animals were capable of the higher function of sexual 
reproduction, but multiplied only in an asexual manner, by 
division or gemmation, by the formation of germ-buds, or of 
germ-cells, as is still the case with most Primseval Animals 
or Protozoa, It was not until a later period in the organic 
history of the earth, that sexual difference of the two 
sexes could arise ; and this took place at first in the 
simplest manner by the severance of two cells which 
amalgamated from the community of the many-celled 
organism. We may say that, in this case, growth, which is 
the condition necessary to reproduction, was attained by 
the union of two full-grown cells into a single cell which 
then exceeded its proper size (" copulation " or conjuga- 
tion"). At first, the two united cells may have been 
entirely alike. Soon, however, by natural selection, a con- 
trast must have arisen between them. For it must have 
been very advantageous to the newly-created individual in 
the struggle for existence, to have inherited various quali- 
ties from the two parent-cells. The complete development 
of this progressive contrast between the two producing 
cells, led to sexual differentiation. One ceU became a 
female egg-ceU, the other, a male seed or sperm celL 

The simplest form of sexual reproduction among existing 
animals, is exhibited in Gastrgeads and the lower Sponges, 
especially the Chalk Sponges, and, also, in the simplest 



39^ 1VE STOUmON OF MAX, 

Hydroid Polyps. In the H&liphyBema (Fig. 315) and in 
the Olynthus the whole body is a simple intestinal pouch, 
which ifl only essentially distinguished from the gastnila by 
the fact that it is adherent by the end opposite the mouih. 
The thin wall of the pouch consists only of the two 
primary germ -layers. As soon as it is sexually mature, 
single cells of the wall become female egg-cells, others 
become male sperm-cells, or seed-cells; the former grow 
very large, as they form a considerable number of yelk- 
granules in their protoplasm (Fig. 181, e); the latter, on the 
contrary, by continued division, become very small, and 
modify into movable "pin-shaped" spermatozoa (Fig. 17, 
vol. i. p. 173). Both kinds of cells sever themselves from their 
birthplace, the primary germ-layers, faU either into the 
surrounding water or into the intestinal cavity, and there 
unite by amalgamation. This is the very important process 
of the fertilization of the egg-ceU by the sperm-cell. (Cf, 
Fig. 18, vol. i. p. 175.) 

These simplest processes of sexual reproduction, as 
exhibited at the present time in the lowest Plant Animals, 
especially in the Chalk Sponges and Hydroid Polyps, inform 
us of several extremely important and significant facts ; 
in the first plawje, we learn, that for sexual reproduction in 
its simplest form, nothing more is required than the 
blending or amalgamation of two differing cells, a female 
egg-cell and a male sperm-cell, or seed-ceU. AH other 
circumstances, and aU the other extremely complex pheno- 
mena, accompanying the act of sexual reproduction in the 
nigher animals, are of a subordinate and secondary charac- 
l;er, and have only attached themselves secondarily to that 
simplest primary process of copulation or fertilization, or 



RELATION OF THE SEXES. 



393 



have arisen by differentiation. But, now, if we consider 
what an extraordinarily important part is ever3rwhere 
played by the relation of the two sexes in organic nature, 
in the vegetable kingdom, as in animal 
and human life ; how the reciprocal 
inclination and attraction of the sexes, 
love, giv.es the impetus of the most 
varied and remarkable processes, is, 
even, one of the most important 
mechanical causes of the hio^hest 
differentiation in life ; — if we consider 
this, we cannot over-estimate this re- 
tracing of " love " to its primitive '^it 
source, to the power of attraction be- 
tween two differing cells. Ever}- 
where throughout animated nature ^/J^^ 



Fig. 315. — Longitudinal section through a 
Haliphysema (Gastrceada) The egg-cells (e) are 
enlarged epithelial cells of the entoderm (g), 
and lie freely in the pi^imitiye intestinal cavity 
{(l): w, mouth-opening ; /j,exoderm. 



the greatest results proceed from this most insignificant 
cause. It is /only necessary to think of the part played in 
nature by the flowers, the reproductive organ of flowering 
plants ; or of the multitude of wonderful phenomena 
caused by sexual selection in animal life ; or, finally, of the 
important influence exerted by love on human life : the coa- 
lescence of two cells is everywhere the single, original 
impelling motive ; everywhere this apparently trivial pro- 




394 THE EVOLUTION OF MAK. 

cess exerts the greatest influence on the development of the 
most varied circumstances. We may, indeed, assert, that 
no other organic process can be, even remotely, compared to 
this in extent and intensity of differentiating effect. For 
is not the Semitic myth of Eve, who seduced Adam to 
knowledge, and is not the old Greek legend of Paris and 
Helen, and are not very many other famous fictions, merely 
the poetical expression of the immeasurable influence, which 
love, in connection with " sexual selection," ^ has exerted, 
ever since the differentiation of the two sexes, on the pro- 
gress of the world's history ? All other passions that agitate 
the human breast are in their combined efiects far less 
powerful than love, which inflames the senses and fools the 
understanding. On the one hand, we gratefully glorify love 
as the source of the most splendid creations of art ; of the 
noblest productions of poetry, of plastic art and of music : 
we reverence in it the most powerful factor in human 
civilization, the basis of family life, and, consequently, of 
the development of the state. On the other hand, we fear 
in it the devouring flame which drives the unfortunate to 
ruin, and which has caused more misery, vice, and crime, 
than all the other evils of the human race taken together. 
So wonderful is love, and so immeasurably important is its 
influence on mental life, on the most varied functions of the 
medullary tube, that in this point, more than in any other, 
" supernatural " causation seems to mock every natural 
explanation. And yet, notwithstanding all this, the com- 
parative history of evolution leads us back very clearly and 
indubitably to the oldest and simplest source of love, to 
the elective aj9&nity of two differing cells : the sperm-cell 
and the egg-cell. 



HERMAPHRODITISM. 395 

Just as the lowest Plant Animals exhibit this most 
simple origin of the complex phenomena of reproduction, 
so, in the second place, they reveal the highly important 
fact, that the earliest and most primitive sexual relation 
was hermaphroditism, and that the separation of the sexes 
originated from this only secondarily (by division of labour). 
Hermaphroditism is prevalent in lower animals of the most 
different groups; in these, each single individual, when 
sexually mature, each person, contains male and female 
sexual cells, and is, therefore, capable of self-fertilization 
and self-reproduction. Thus, not only in the lowest Plant 
Animals just mentioned (the Gastrseads, Chalk-sponges, 
and many Hydroid Polyps) do we find egg-cells and 
sperm-cells united in one and the same person ; but 
many Worms (for example, the Ascidians, Eaiih Worms 
and Leeches), many Snails (the common garden Snail), and 
many other invertebrate animals are also hermaphrodite. 
All the earlier invertebrate ancestors of man, from the 
Gastrseada up to the Chordoma, must also have been her- 
maphrodite. So, probably, were also the earliest Skulled 
Animals (Figs. 52-56, e, h, vol. i. p. 256). One extremely 
weighty piece of evidence of this is afforded by the remark- 
able fact, that even in Vertebrates, in Man as well as other 
Vertebrates, the original rudiment of the sexual organs is 
hermaphrodite. The separation of the sexes (Oonocho- 
rism). the assignment of the two kinds of sexual cells 
to ditierent individuals, originated from hermaphroditism 
only in the farther course of tribal history. At first, male 
and female individuals differed only in the possession of the 
two kinds of cells, but in other respects were exactly alike, 

ia now the case in the Amphioxus and the Cyclostoma. 



396 THE EVOLUTION OF MAN. 

Not until a later period, by the law of sexual selection, so 
briUiantly elucidated by Darwin, were developed the so- 
called " secondary sexual characters," that is, those dif- 
ferences in the male and female sexes which are exhibited, 
not in the sexual organs themselves, but in other parte of 
the body (for example, the beard of the man, the breast of 
the woman).* 

The third important fact, taught us by the lower Plant 
Animals, refers to the earliest origin of the two kinds of 
sexual cells. For, as in Gastrseads, and in many Sponges and 
Hydroids, in which we meet with the simplest rudiments 
of sexual differentiation, the whole body consists throughout 
life only of the two primary germ-layers, the two kinds of 
sexual cells can, therefore, only have originated from cells 
of the two primary germ-layers. This simple discovery is 
of extreme importance, because the question of the first 
origin of the egg-cells as well as of the sperm-cells in the 
higher animals — and especially in Vertebrates — presents 
unusual difficulties. In these animals it usually appears 
as if the sexual cells developed, not from one of the two 
primary, but from one of the four secondary germ-layers. 
If, as most authors assume, they do originate from the 
middle-layer, or mesoderm, the fact is due to an ontogenetic 
heterotopism, to a displacement in position. (Cf vol. i. p. 13.) 
Unless the unjustifiable and paradoxical assumption, that 
the sexual cells are of entirely different origin in the higher 
and in the lower animals, is accepted, we are compelled to 
derive them originally (phylogenetically), in the former as in 
the latter, from one of the two primary germ-layers. It must 
then be assumed that these cells of the skin-layer or of 
the intestinal layer, which must be regiuxled as the earliest 



OBIQIN OF THE SEXUAL CELLS. |97 

progenitors of the sperm-cells and of the egg-cella, with- 
drew, during the separation of the skin-fibrous layer from 
the skin-sensory layer, or of the intestinal-fibrous layer 
fi'om the intestinal-glandular layer, into the body-cavity 
oceloTna), which was in process of formation; and that 
they thus acquired the internal position between the two 
fibrous layers, which appears as their original position, 
when the sexual cells first become distinct in the vertebrate 
embryo. Otherwise, we should be obliged to accept the 
improbable polyphyletic hypothesis, that the origin of the 
egg-cells and sperm-cells is different in the higher and in 
the lower animals, that their origin in the former ia inde- 
pendent of that in the latter. 

K we, accordingly, derive the two kinds of sexual cells 
from the two primary germ-layers in man as in all other 
animals, the farther question arises : Did the female egg- 
cells and the male sperm-cells develop from both primary 
germ-layers, or fit)m one only ? and, in the latter case, from 
which of the two ? This important and interesting question 
is one of the most difficult and obscure problems in the 
history of evolution, and, up to the present moment, no full 
and clear solution has been attained. On the contrary, 
the most opposite answers are given to it even yet by 
naturalists of note. Among the various possible solutions 
only two have been generally considered. It has been 
supposed that both kinds of sexual cells originally de- 
veloped from the same primary germ-layer, either from the 
skin-layer or the intestinal layer ; but almost as many and 
as able observers have accepted the one as the origin as 
the other. Quite recently the Belgian naturalist, Eduard 
▼an Beueden, has asserted, on the contrary, that the ^g-ce^ 



39^ THE EVOLUTION OF MAN. 

originate from the intestinal layer, the sperm-colls from the 
skin-layer.^^^ In Gastraeads, Sponges, and Hydro-medusae 
this appears really to be the case. The development of the 
sexual differences, which is so rich in results, must, ac- 
cordingly, have commenced even during the differentiation 
of the two primary germ-layers in the simplest and lowest 
^ant Animals ; the exoderm would be the male germ-layer, 
the entoderm, the female. If this discovery of Van Beneden 
is established and proves to be a universal law, Biology wiU 
gain a most pregnant advance ; for not only would all the 
contradictory empiric explanations be answered, but a new 
path would be opened for philosophic reflection on one of 
the most important of biogenetic processes. 

K we now trace the Phylogeny of the sexual organs 
in our earliest Metazoic ancestors further, as it is indicated, 
at the present time, in the Comparative Anatomy and 
Ontogeny of the lowest Worms and Plant Animals, we 
note, as the first advance, the accumulation of the cells of 
both sexes into definite groups. While in Sponges and 
the lowest Hydra-Polyps single scattered cells separate from 
the cell-layers of the two primary germ-layers, and become 
isolated and free sexual cells, in the higher Plant Animals 
and Worms we find these same cells associated and col- 
lected into groups of aggregate cells, which are, hence- 
forward, called " sexual glands," or " germ-glands " (gonades). 
It is only now that we can speak of sexual organs in the 
morphological sense. The female germ-glands which, as 
such, in their simplest form constitute a mass of homo- 
genous egg-cells, are the ovaries (ovaria, or oophora; Fig. 
211, e, p. 198). The male germ-glands, which in their 
joimitive form also consist merely of a mass of sperm-cellsj 



DXYELOPMENT OF THE SEXUAL OmaJJKM. 599 

the testes (testiculi, or orchides; Fig. 211, ^). We find 
the ovaries and testes in this earliest and simplest shape 
not only in many Worms (Annelida) and Plant Animals, 
but also in the lowest Vertebrates, in the Skull-less Animals 
(Acranid). In the anatomy of the Amphioxus we found the 
ovaries of the female and the testes of the male consisting 
of twenty to thirty elliptic or roundly four-cornered simple 
sacs, of small size, attached to the inside of the gill-cavity 
on each side of the intestine. (Cf. voL i. p. 425.) 

Only a single pair of germ-glands, lying far down in the 
floor of the body-cavity (Fig. 316, g), exist in all Skulled 
Animals (Graniota). The first traces of these appear in the 
coelom-epithelium. Probably, in this case also, the male 
sperm-cells originate from the skin-layer, the female egg- 
cells, on the contrary, from the intestinal layer. The earliest 
traces are visible in the embryo at the point where the 
skin-fibrous layer and the intestinal-fibrous layer meet in 
the middle plate (mesentery-plate) (Fig. 318, mp, p. 408). 
At this very important point in the ccelom-wall, where the 
endocoelar (or visceral coelom-epithelium) merges into the 
exocoelar (or parietal coelom-epithelium), in the embryo of 
Man and the other Skulled Animals a small aggregation ol 
cells becomes visible, at a very early period, and this, accord- 
ing to Waldeyer,^^^ we may call the " germ-epithelium," or 
(corresponding with the other plate-shaped rudiments of 
organs) the sexual plate (Fig. 316, y ; Plate IV. Fig. o,k). The 
cells of this germ-plate, or sexual plate (la/mella sexualis) are 
essentially distinguished by their cylindrical form and by 
their chemical constitution from the other cells of the 
coelom ; they are of quite difierent significance from the flat 
o«lk oi the ''seroiu coelom-epithelium" which line the 

59 



400 



THE EVOLUTION OF MAN. 



remainder of the body-cavity (coeloma). Of tliese latter — 
the true ccjelom -cells — those which invest the intestinal 
tube and the mesentery (" endocoelar ") originate from the 




Fig. 316, — Transverse section . through the pelvic region and the hind 
limbs of an embryo Chick in the fourth day of incubation, enlarged about 
40 tirjies : h, horn-plate ; w, medullary tube ; n, canal of the medullary 
tube ; u, primitive kidneys ; x, notochord ; e, hind limbs ; b, allantois canal 
in ventral wall; t, aorta; v, cardinal veins'; a, intestine; d, intestinal- 
glandular layer; /, intestinal-fibrous layer; g, germ-epithelium • r, dorsal 
muscles ; c, body-cavity, or Coelom. (After Waldeyer.) 

intestinal-fibrous layer (in Fig. 5, Plate IV., coloured red) ; 
those which line the inner surface of the external wall of 
the abdomen (" exocoelar ") are, on the contrary, the product 
of the skin-fibrous layer (coloured blue in Fig. 5, Plate I\\) ; 
but the sexual cells which make their appearance at the 
boundary line between the two forms of coelom-cells, and 



DIFFEBENTIATION OF THE SEXES. 4OI 

which insert themselves, to a certain extent, between the 
endocoelar and the exocoelar, there forming the germ- 
plate, cannot be referred either to the intestinal-fibrous 
layer or to the skin-fibrous layer, but directly to the two 
primary germ-layers; for there are important grounds for 
supposing that even the first rudiment of the sexual plate is, 
probably, hermaphroditic, and that this " sexual epithelium " 
(visible, in Man and all other Vertebrates, between the exo- 
coelar and the endocoelar) represents a primaeval and simple 
hermaphrodite gland. (Cf. voL L p. 256, Figs. 52-56, e, h.) 
The inner half of this, in contact with the intestinal-fibrous 
.ayer, which is derived from the intestinal-glandular layer, 
would be the rudiment of the ovary; its outer half, in 
contact with the skin-fibrous layer, which originates from 
the intestinal-glandular layer, would be the rudiment of the 
testes. This is, of course, only conjectural. 

We ought, accordingly, to distingiiish two different 
sexual plates or germ-epithelia ; the female sexual plate, a 
product of the intestinal layer, which gives rise to the 
ovary-epithelium — the mother ^cells of the ova (" ovary- 
plate ") ; and the male sexual plate, lying externally over the 
former, and which is a product of the skin-layer, from which 
originates the testes-epithelium — the mother cells of the 
sperm-threads (" testes-plate '*) ; but even the first recog- 
nizable rudiments of the two sexual plates appear, indeed, 
Bo intimately associated in the human embryo and in those 
of the higher Vertebrates, that hitherto they have been re- 
garded as a single, undifferentiated, common rudiment of an 
organ ; and it is still possible that- the two kinds of sexual 
glands arise by secondary differentiation from a conimon 
rudiment. 



402 THE EVOLUTION OF MAN. 

Though we must recognize the formation of the two 
kinds of sexual cells, and in their union at fertilization as 
the one essential act of sexual reproduction, yet, in the great 
majority of animals, other organs exist which also take 
part in the act of fertilization. The most important of 
these secondary sexual organs are the exit-ducts which 
serve to conduct the mature sexual cells out of the body, 
and, next to these, the copulative organs, which transmit 
the fertilizing sperm from the male person to the female, 
in which the eggs are situated. These latter organs exist 
only in the higher animals of various tribes, and are far less 
widely distributed than the exit-ducts. Even these latter, 
however, are only of secondary formation, and are wanting 
in many animals of the lower groups. In these, as a rule, 
the mature sexual cells are simply ejected from the body. 
In some cases they pass out directly through the outer 
skin-covering (as in the Hydra and many of the Hy- 
droidea) ; in other cases, they enter the stomach-cavity, 
and are ejected through the mouth-opening (in Gastrseads, 
Sponges, and other Hydro^ Polypes and Coral Animals) ; 
in yet other cases, they enter the body-cavity and 
pass out through a special aperture in the ventral wall 
(poru8 genitalia). The latter is the case in many Worms 
and even in a few lower Vertebrates (Cyclostoma and 
a few Fishes). These indicate the earliest condition of 
lids matter as it was in our ancestors. On the other 
hand, in aU higher, and most lower Vertebrates (as also 
in most higher Invertebrates) special tube-shaped exit- 
ducts from the sexual cells, or sexual ducts (gonophori), 
are present in both sexes. In the female these convey the 
egg-cella out from the ovaries, and hence they have bees 



SGO-BUGTS AND SPfiRM-DUCm. 403 

called egg-ducts {oviductus, or tuhoe faZlopice). In the 
male sex these tubes convey the sperm-cells from the testes, 
and hence they are called sperm-ducts (spermddiLctua, or 
vasa deferentia). 

The original, genetic condition of these two outlets 
is exactly the same in Man as in all higher Vertebrates, 
while in most Invertebrates it is entirely different; for 
while in the latter the sexual ducts develop directly from 
the sexual glands, or from the external skin, or from the in- 
testinal canal, in Vertebrates an organ-system is employed 
for the conveyance of the sexual products ; one which origin- 
ally had a very different significance and function — the 
kidney system, or urinary organs. The original, primary func- 
tion of these organs is simply to eliminate useless matter 
from the body in a liquid form. The liquid product of this 
secretion is called the urine, and is discharged either directly 
through the external skin, or through the last section of the 
intestine. The tube-shaped " urinary ducts " only second- 
arily absorb the sexual products also and convey them out ; 
they thus become "urogenital dticts" (ductus urogenitates). 
This remarkable secondary combination of the urinary and 
the sexual organs into a common " urogenital apparatus," or 
** urogenital system," is highly characteristic of the higher 
Vertebrates. In the lowest of these it is, however, wanting, 
while, on the other hand, it is foimd in the higher Ringed 
Worms (Annelida). To estimate this rightly, we must first 
glance at the comparative economy of the urinary organs 
as a whole. 

The kidney system or urinary system (aystema uro- 
poeticum) is one of the earliest and most important organ- 
systems in the differentiated animal body, as has already 



404 THE EVOLUTION OF MAK. 

been incidentally mentioned (Cf. Chapter XVII.) It is 
found almost universally distributed, not only in the higher 
animal tribes, but even in the more primitive Worm tribe. 
Among the latter it even occurs in the lowest and most 
imperfect known Worms — the Flat Worms (Plathelminthes) 
(Fig. 184, nc, p. 80). Although these acoelomatous Worms 
have no body-cavity, no blood, no vascular system, they 
always have a kidney system. It consists of a pair of 
simple or of branched canals, lined by a layer of ceUs, which 
absorb useless juices from the tissues and discharge them 
through an external skin-opening (Fig. 184, n/m). Not 
only the free-living Gliding Worms (Turhellaria), but also 
the parasitic Sucking Worms (Trematoda), and even the 
still more degraded Tape Worms, which, in consequence 
of their parasitic habit of life, have lost their intestinal 
canal, are all provided with these " kidney canals " or primi- 
tive kidneys. Usually these canals in the Worms are called 
excretory organs, and in former times they used to be caUed 
water-vessels. PhylogeneticaUy they must be regarded as 
highly-developed pouch-like skin-glands resembling the 
sweat-glands of Mammals, and, Mke these, developed from 
the skin-sensory layer. (Cf. Fig. 210, n, p. 198, and Fig. 214, 
p. 202.) 

While in these lowest unsegmented Worms only a single 
pair of kidney ducts is present, in the higher segmented 
Worms these ducts exist in greater numbers. In Ringed 
Worms (Annelida), in which the body is composed of a 
great number of segments, or metamera, a pair of these 
primitive kidneys (hence known as segmental organs, or 
canals) exists in each separate segment. In this case, also, 
the canals are very simple tubes, which, on account of theii 



THE PRIMITIVE KIDNKTH. 4O5 

ooiled or looped form, are called " coiled canals." To the 
primary, external aperture in the outer skin, originally 
alone present, a secondary, internal aperture into the body- 
cavity {coeloma) is now added This opening is provided 
with vibratory cilia, and is thus enabled to absorb the 
secretional juices from the body-cavity and to discharge 
them from the body. Now in these Worms also the sexual 
cells, which develop in the simplest form upon the inner 
surface of the abdominal wall, pass, when mature, into the 
coelom, are drawn into the internal, funnel-shaped ciliated 
openings of the kidney canals, and are carried out of the 
body with the urine. Thus the urine-forming "coiled 
canals," or " primitive kidneys," serve, in the female Ringed 
Worms, as " oviducts," and, in the male, as " sperm-ducts." 

It would of course be most interesting to know the 
condition, on this point, of the Amphioxus, which, standing 
midway between Worms and Vertebrates, affords us so 
much valuable information. Unfortunately this animal, 
for the present, affords no solution of this matter. At 
present we know nothing certainly as to the relation 
between the urinary and the sexual organs of the Amphi- 
oxus. Some zoologists assert that this animal has no 
kidneys ; others regard the two long " side canals " as 
atrophied primitive kidney ducts (Fig. 162, S, vol. i. p. 423) ; 
yet others consider certain glandular epidermis-swellings on 
the inner surface of the gill-cavity to be rudimentary kidneys. 
Most probably, a great reversion has affected the original 
primitive kidney canals in the Amphioxus, amounting per- 
haps to their entire phylogenetic loss. 

Very interesting inferences may be drawn from the 
Vertebrates of the next stage — the Monorhina, or Cyclod- 



40« 



THE EVOLUTION OF MAN. 



toma. Although both orders of this class — ^the Myxinoides 
as well as the Petromyzontes — possess developed, urine- 
secreting kidneys, these organs do not in this case serve to 
carry away the sexual cells. These cells pass directly from 
the germ-glands into the coelom, and are discharged through 
a posterior aperture in the abdomen. The condition of the 
primitive kidneys in these is, however, very interesting, and 

throws light on the complex kidney 
structure of the higher Vertebrates. 
In the first place, in the My^xi- 
noides (Bdellostoma) we find a long 
tube, the primitive kidney duct 
(protureter, Fig. 317, a), on each 
side. This opens internally into 
the coelom through a ciliated funnel- 
shaped aperture (as in Ringed 
Worms) ; it opens externally through 
an opening in the outer skin. A 
oreat number of small horizontal 
tubes (" segmental canals," or primi- 



FiG. 317.—^. Portion of kidney of Bdel- 
lostoma : a, primitive kioney duct (jprotu- 
reter); h, segmental canals, or primitive 
urine canals (tuhuli uriniferi) ; c, kidney, 
vesicles (capsulae Malphigianoe'), — B. Por- 
tion of the same, much enlarged : c, kidney. 
vesicle, with the glomeruhia ; d, approaching 
artery ; «, retreating artery. (After Johannes 
Miiller.) 




fcive urine tubes) open on its inner side. Each of these 
terminates in a blind, vesicular capsule (c) enclosing a 



THE PRBHTIYE KEDNET OF SKULLED ANIMALS. 4O7 

knot of blood-vessels (glomervZua, an arterial net. Tig. 
317, B, c). Afferent arterial branches (vasa afferentia) con- 
vey arterial blood into the coiled branches of the "glome- 
rulus" (d), and efferent arterial branches (vasa effererUia) 
again carry it out of the glomerulus (e). 

In Primitive Fishes (Selachii) also there is a longitudi- 
nal series of segmental canals, which open outwardly in 
the primitive kidney ducts. The segmental canals (a pair 
in each metameron of the central part of the body) open, in 
this case, freely into the body-cavity, through a ciliated 
funnel (as in Ringed Worms, or Annelids). A part of this 
organ forms a compact primitive kidney, while the rest is 
employed in the formation of the sexual organs. 

The primitive kidney in the embryo of Man and in that 
of all other Skulled Animals (Craniota) is first formed in 
the same simple shape which persists throughout life in 
Myxinoides, and partly in Selachii. We found this primi- 
tive organ in the human embryo at that early period just 
succeeding the separation in the skin-sensory layer, of the 
medullary tube from the horn-plate, and the differentiation, 
in the skin-fibrous layer, of the notochord, the primitive 
vertebral plate, and the skin-muscle plate. As the first 
rudiment of the primordial kidneys, a long thin, thread-like 
string of cells, which is soon hollowed out into a canal, 
appears in this case, on each side, immediately below the 
horn-plate ; this extends in a straight line from front to 
back, and is plainly seen in the cross section of the embryo 
(Fig. 318) in its original position in the space between the 
horn-plate (A), the primitive vertebrae (uw), and the skin- 
muscle plate (hpl). The first origin of this primitive 
kidney duct is still a matter of dispute, some ontogenista 



408 - THE EVOLCTTION OF MAN. 

referring it to the horn-plate, others to the primitive ver- 
tebral plate, and yet others to the skin-muscle plate. Pro- 
bably its earliest (phylogenetic) origin is to be found in the 
skin-sensory layer ; but it very soon quits its superficial 



ch u>r ao sp <^<^ '^f 

Fig. 318. — Transverse section through the embryo of a Chick, on the 
second day of incubation : h, horn-plate ; m, medullary tube ; ung, primitive 
kidney duct ; ch, notochord ; mv, primitive vertebral cord ; h'pl, skin- 
fibrous layer ; df, intestinal-fibrous layer ; m/p, mesentery-plate, or middle 
plate (point of attachment of the two fibrous layers) ; sp, body-cavity 
(cosloma) ; ao, primitive aorta ; dd, intestinal-glandular layer. (After 
Kolliker.) 

position, passes inward, between the primitive vertebral 
plates and the side plates, and finally lies upon the inner 
surface of the body-cavity. (Cf Figs. 66-69, u, vol. i. p. 277, 
^ and Figs. 95-98, p. 319; also Plate IV. Figs. 3-6, u.) While 
the primitive kidney duct is thus making its way inward, 
on its inner and under side appear a large number of small 
horizontal tubes (Fig. 319, a), exactly corresponding to the 
segmental canals of the Myxinoides (Fig. 317, h). Like the 
latter, these are, probably, originally protuberances of the 
primitive kidney ducts (Fig. 316, t^). At the blind, inner 
end of each of the primitive urinary tubes an arterial 
glomerulus is formed, which grows into this blind end 
from within, forming a " vascular coil." The glomerulus 
t(j a certain extent expands the bladder-like blind end 
of the small urinary tubes. As the primitive urinary tubes, 



RUDIMENTARY PRIMITIVE KIDNEYS. 



409 



which are, at first, very short, grow longer and broader, 
each of the two primitive kidneys assumes the form of a 
semi-pinnate leaf (Fig. 320)ii fThe urinary tubes (u) repre- 





FiG. 319. — Rudimentary primitive kidney of embryonic Dbg. The pos- 
terior portion of the body of the embryo is seen from the ventral side, 
covered by the intestinal layer of the yelk-sac, which has been torn away, 
and thrown back in front in order to show the primitive kidney ducts with 
the primitive kidney tubes (a) : h, primitive vertebrae ; c, dorsal medulla ; 
d, passage into the pelvic intestinal cavity. (After Bischoff.) 

Fig. 320. — -Primitive kidney of a human embryo : n, the urine-tubes of 
the primitive kidney ; iv, Wolffian duct ; iv', upper end of the latter (Mor- 
gagni's hydatid) ; m, Miillenan duct ; m', upper end of the latter (Fallopian 
hydatid) ; g, hermaphrodite gland. (After Kobelt.) , 



sent the tissue and the primitive kidney duct (tu) the 
mid-rib. On the inner margin of the primitive kidney the 
rudiment of the hermaphrodite sexual gland already 



410 THE EVOLUTION OF MAK. 

appears as a body of considerable size. The posterior end 
of the primitive kidney duct opens into the lower extremity 
of the last section of the rectum, so that this organ becomes 
a cloaca But this opening of the primitive kidney duct 
into the intestinal canal must be regarded, phylogenetically, 
as a secondary condition. Originally, as is indicated clearly 
in the Cyclostoma, they issued through the external abdo- 
minal skin, quite independently of the intestinal canal, thus 
proving their early phylogenetic origin from the horn-plate, 
as outer skin glands. 

While in the Myxinoides the primitive kidneys per- 
manently retain this simple form, as they do partially in 
Primitive Fishes (Selachii), in all other Craniota it appears 
only temporally in the embryo, as the ontogenetic repro- 
duction of the primordial phylogenetic condition. In these 
Skulled Animals the primitive kidney, by vigorous growth, 
increases in length, and by the increase in number and the 
coiling of the urinary tubes, very soon assumes the form of 
a large compact gland, of oblong, oval, or spindle-shaped 
form, which extends longitudinally through the greater 
part of the body-cavity {coeloraa) of the embryo (Figs. 123,m, 
124,m, vol. i. p. 370). In this case, it lies near the middle line, 
directly under the primitive vertebral column, and extends 
from the region of the heart to the cloaca. The right and 
left primitive kidneys lie parallel and close together, being 
separated only by the mesentery, that narrow, thin lamella 
which connects the central intestine with the lower surface 
of the primitive vertebral column. The excretory duct of 
each primitive kidney, the protureter, traverses the lower 
and outer side of the gland in a posterior direction, and 
opens into the cloaca, dose to the root of the aUantois ; at 



WOLFFIAN BODIES. 4 II 

a later period, it opens into the allantois itself (Fig. 136, o. 
voL i. p. 381). ' 

The primitive kidney (primordial kidney) in the embr}''o 
of Amniota was formerly called the " Wolffian body," also 
the " Okenian body." In all cases it acts for a time as a 
true kidney, draining and secreting the useless fluids of the 
embryonic body, and discharging them into the cloaca and 
then into the allantois. The " primitive urine " collects in 
the latter organ, and hence the allantois in the embryo of 
man and of the other Amniota acts as a real urinary bladder, 
or " primitive urinary sac ; " yet it is in no way geneti- 
cally connected with the primitive kidneys, but is rather, 
as we have already seen, a pouch-like protuberance of the an- 
terior wall of the terminal intestine (Fig. 135, u, vol. i. p. 380), 
The allantois is, therefore, a product of the intestinal layer, 
while the primitive kidneys are a product of the skin- 
layer. Phylogenetically we must conceive that the allan- 
tois originated as a pouch-shaped protuberance of the 
cloacal wall resulting from the distension caused by the 
collection in the cloaca of the primitive urine secreted 
by the primordial kidneys. It is, originally, a blind sac 
belonging to the rectum (Plate V. Fig. 15, Kb). The true 
urinary bladder of Vertebrates, evidently, first appeared in 
Dipneusta (in the Lepidosiren), and was thence transmitted, 
first to the Amphibia, and then to the Amniota. In the 
embryo of the latter it protrudes far out of the yet unclose<l 
abdominal wall. Many Fishes, indeed, also possess a so- 
called urinary bladder. But this is merely a local disten- 
sion in the lower section of the primitive kidney ducts. 
and hence, both in origin and in constitution, is essentially 
distinct from the true urinary bladder. The two structures 



413 THE ETOLUTION OF MAN. 

are only physiologically comparable; they are, therefore, 
analogous, as having the same function; morphologically, 
however, they are not to be compared, or are not homo- 
logous.^® The false urinary bladder in Fishes is a pro- 
duct of the primitive kidney duct, therefore of the skin- 
layer; the true urinary bladder in Dipneusta, Amphi- 
bia, and Amniota is, on the contrary, a blind-sac of the 
terminal intestine, and hence a product of the intestinal 
layer. 

In all low Skulled Animals {Graniota), without amnion 
(in Cyclostoma, Fishes, Dipneusta, and Amphibia), the 
urinary organs remain in an inferior stage of development, 
in so far as the primitive kidneys (protonepkra), though 
much modified, here act permanently as urine-secreting 
glands. In the three higher vertebrate classes, included in 
the term Amnion Animals, on the contrary, this is the case 
only for a short period during early embryonic life. The 
permanent, or secondary kidneys (renes, or metanephra), 
which are peculiar to these three classes, are very early 
developed. These originate, not (as was long believed, on 
the authority of Remak) as entirely new, independent 
glands of the intestinal tube, but from the posterior section 
of the primitive kidney duct (protureter). From the latter, 
near where it opens into the cloaca, a simple pouch — the 
secondary kidney duct — grows out, and this increases con- 
siderably in length forwards; from the blind, upper, or 
anterior portion of this the permanent kidney originates, 
precisely as the primitive kidney originates from the pri- 
mitive kidney duct. The secondary kidney duct gives rise 
to a number of small blind tubes — the secondary urinary 
tabes — and the blind capsule-shaped ends of these 



THK SECONDARY KIDNETSw 413 

are occupied by vascular coils {glomervli). The further 
growth of these tubes results in the compact secondary 
kidney, which, in Man and most higher Mammals, acquires 
the well-known bean-like form ; in the lower Mammalia, 
in Birds and in Reptiles, on the other hand, it is separated 
into several lobes. The lower, or posterior part of the 
permanent kidney duct retains the form of a simple canal, 
widens, and thus forms the permanent urine duct {ureter). 
At first this canal, yet united with the last section of the 
primitive kidney duct, discharges into the cloaca; at a 
later period, it separates from the primitive kidney duct, 
and yet later from the rectum, and then it discharges into 
the permanent urinary bladder {vesica urinaria). The 
latter originates from the posterior, or lower part of the 
stalk of the allantois (urachus), which widens and becomes 
spindle-shaped before opening into the cloaca. The anterior, 
or upper part of the allantois-stalk, which passes in the 
abdominal wall of the embryo to the navel, afterwards 
disappears, a useless cord-shaped remnant alone remaining 
as a rudimentary organ : this is the single urinary-bladder 
navel-cord (ligamentwfn vesico-v/mbilicale mediwm). On 
the right and left of this, in the adult Man, there are two 
other rudimentary organs : the lateral urinary-bladder navel- 
cords (ligamenta vesico-umhilicalia lateralia). These are 
the obsolete cord-Kke remnant of the former navel-arteries 
{arterioB vmibilicales, vol. i. p. 400 ; Fig. 326, a). 

Although in Man, as in all other Amnion Animals, the 
primitive kidneys are thus very early displaced by the 
secondary kidneys, and although the latter alone afterwards 
act as urinary organs, the former are not, however, alto- 
gether discarded. Indeed, the primitive kidney ducts acquii e 



414 



THE EVOLUTION OF MAN. 



a high physiological significance, as they modify into 
cretory ducts of the sexual glands. In all Amphirhina or 
Gnathostomi — therefore in all Vertebrates from Fishes up 
to Man — at a very early period, a second similar canal 
appears in the embryo at the side of each primitive kidney 
duct. This canal is commonly called, after its discoverer, 
Johannes Muller, " Miiller's duct " (ductus Mulleri), while 
the earlier, primitive kidney duct is distinguished as the 
"Wolffian duct" {ductus Wolfii). The actual origin of 
Miiller's duct is still undetermined ; Comparative Anatomy 
and Ontogeny seem, however, to indicate that it proceeds 
by differentiation from the Wolffian duct. It is, probably, 
most correct to say, that the original (primary) primitive 
V kidney duct breaks up by difierentiation (or fission) into 
two secondary, similar ducts; these are the Wolffian and 




Jhtk. 321. — Primitive kidneya and rudiments of the sexnal orgam. A and 
B, of Amphibia (Frog larvae) ; A, earlier, B, later condition. 0, of a Mam- 
mal (embryo of Ox) : u, primitive kidneys ; k, sexual glands (rudiments of 
testes and ovaries). The primary primitive kidney duct (ug in Fig. A) 
separates (in B and C) into the two secondary primitive kidney ducts ; the 
Miillerian duct (») and the Wolffian duct (u9')> which unite behind into a 
genital oord (gr) ; I, groin-oord of the primitive kidneys. (Aftar Qegenbaor.) 



DEVELOPMENT OF THE WOLFFIAN DUCTa 



415 



the Mullerian ducts. The latter (Fig. 320, w) lies imme- 
diately inside the former (Fig. 320 m). Both open pos- 
teriorly into the cloaca. 

Obscure and uncertain as 
is the origin of the Mullerian 
and Wolffian ducts, their later 
history is clear and definite. 
In all Double-nostrilled (^m- 
phirhina) and Jaw-moutbed 
(Ghuithostoini) animals, from 
Primitive Fishes up to Man, 
the Wolffian duct becomes the 
seed-duct, and the Miillerian 
duct, the oviduct. In each 
sex only one of these is per- 

Fios. 322, 323. — Urinary and sexnal 
organs of an Amphibian (Water- Newt, 
or Triton). Fig. 322 (A), female; 
Fig. 323 (B), male : r, primitire kid- 
ney ; ov, ovary ; od, egg -dnct and 
Rathke'e duct, both formed from the 
Mullerian duct ; u, primitive urinary 
duct — acting, in man, also as seed- 
duot (v«) — opening below into WolfFs 
duct (tt') ; ms, ovary-mesentery {ma- 
ova/rwm). (After Gegenbaur.) 

sistent; the other entirely disappears, or leaves only a 
remnant as a rudimentary organ. In the male sex, in 
which the two Wolffian ducts become sperm-ducts, certain 
rudiments of the Mullerian duct are often found, which 
we will caU " Rathke's canals " (Fig. 323, c). In the female 
«ex, where, on the contrary, the two Miillerian ducts 
60 




4i6 



THE EVOLUTION OF MAN. 



become oviducts, traces of the Wolffian ducts remain, and 
are known as " Gartner's canals." 



'iiri"Ti'"«r,«i,'^)^''^"iv 



3. 




FlOS. 324-326. — Urinary and sexnal organs of an embryonic Ox. Fig. 
324, of female embryo of 1^ inch in length ; Pig. 325, of male embryo 
of 24 inches in length ; Fig. 326, of female embryo of 2^ inches in length : 
w, primitive kidney ; wg, Wolff's duct ; n», Miiller's duct ; m', upper end of 
he latter (opened at <)> *> lower thickened end of the same (rudiment 
of otenu) ; g, genital cord j h, testes {h', lower, h", upper testis-oord) ; 
0, orary ; 0', lower ovary-cord ; t, groin-cord of the primitive kidney ; 
d, diaphragm>oord of the primitive kidney ; n, permanent kidneys (below 
these the S-shaped urine-duct ; between the two the reotmn) ; v, urine- 
bladd«r ; a, navel-artery. (After KSlliker.) 



The most interesting facts in reference to this remark- 
able development of the primitive kidney ducts and their 
anion with the sexual glands are exhibited in Amphibia 
(Figs. 321-323). The first rudiment of the primitive kidney 
ducts and their differentiation into the Miillerian and 



DEVELOPMENT OF THE HUKAN KIDNKT. 417 

Wolffian ducts is identical in both sexes, as is the case in 
the embryos of Mammals (Fig. 321, G, Fig. 324). In the 
female Amphibia the Miillerian duct on each side develops 
into a large ovary (Fig. 322, od), while the Wolffian duct acts 
permanently as a urinaiy duct {n). In the male, on the 
contrary, the Miillerian duct persists only as a rudimentary 
organ, without functional significance, as Rathke's canal 
(Fig. 323, c) ; the Wolffian duct serves, in this case also, as a 
orinary duct, but also as a sperm or seed duct, the seminal 
tubes (ye) from the testes (t) entering the upper part of the 
primitive kidneys, and there uniting with the urinary canals. 

In Mammals these conditions, persistent in Amphibia, are 
rapidly traversed by the embryo in an early period of its 
development (Fig. 321, G). The primitive kidneys, which 
in non-amnionate Vertebrates persist throughout life as the 
urine-secretory organ, are superseded by the secondary 
kidneys. The actual primitive kidneys disappear almost 
entirely in the embryo at an early period, leaving but small 
traces. In the male Mammal the supplementary testis 
(epididymis) develops from the upper part of the primitive 
kidney ; in the female the same part gives rise to a useless 
rudimentary organ, the supplementary ovary (parovarvu/m) 

In the female Mammal the Miillerian ducts undergo very 
considerable changes. The actual ovaries develop only from 
its upper part ; the lower part widens out into a spindle- 
shaped pouch, with a thick, fleshy wall, within which the 
fertilized egg develops into the embryo. This pouch is the 
womb (uterus). At first the two uteri are perfectly 
separate, and open on each side of the urine-bladder (vu) 
into the cloaca, as is yet permanently the case in the 
lowest living Mammals, the Beaked Anima.1s (Omithosftcma) ; 



4i8 



THE EVOLUTION OF MAN. 




but even in Pouched Animals (Marsupialia) sl connection 
forms between the two Mullerian ducts, and in Placental 
Animals they coalesce below with the rudimentary Wolffian 

ducts, forming with them a single 
"sexual cord" (funiculus geni' 
talis).- But the original indepen- 
dence of the two parts of the 
uterus, and of the two vagina 
canals which proceed out of their 
lower extremities, persists in many 
lower Placental Animals, while in 
the higher members of the same 
group, these organs gradually 
coalesce to form one single organ. 

Fig. 327.— Female sexual The process of COaleSCence ad- 
organs of a Beaked Animal vances steadily from below (or 

(Omithorhynchus, Figs. 195, i i • i\ i / n 

196): 0, ovaries; t, oviduct; ^om behmd) upwards (or for- 
u, uterus ; sug, urinary sexual wards). While in many Gnawing 
cavity {sinus urogenitalis); the j^^;^^^^^^ (Rodeutia, e.g., Hares and 

two parts of the uterus open ^ ^ ' u ^ 

into this at u' : ci, cloaca. Squirrels) two separate uteri open 
(After Gegenbaur.) jj^^^ |]-^g vagina canal which has 

already become simple, in other Gnawing Animals, as also 
in Beasts of Prey, Whales, and Hoofed Animals {Ungulata), 
the lower halves of the two uteri are already coalescent, 
their upper halves (the so-called horns, "cornua") remaining 
distinct (" uterus hicornis "). In Bats and Semi-apes these 
upper horns are very short, while the unified lower part 
becomes longer. Finally, in Apes, as in Man, th^ cohesion 
of the two parts is complete, one simple pear-shaped uterus- 
pouch alone remaining, and into this the oviducts open on 
^ach side, 



POSITION OF THE HUMAN SEXUAL onOANft. 4t^ 

In the male Mammal also, a similar coalescence of the 
lower portion of the Mullerian and Wolffian ducts takes 
place. In this case also, these ducts form a single " sexual 
cord " (Fig. 325, g), which likewise opens into the original 
urinary sexual cavity (sinus urogenitalis), which develops 
from the lower part of the urinary bladder (v). While, 
however, in the male Mammal the Wolffian ducts develop 
into the permanent sperm-ducts, only very slight traces of 
the Miillerian ducts remain as rudimentary organs. The 
most remarkable of these is the " male uterus " (tUerus 
masculinus), which originates from the lowest, coalescent 
portion of the Miillerian ducts, and which is homologous 
with the female uterus. It forms a small flask-shaped 
vesicle, entirely without physiological significance, which 
opens into the urinary tubes between the two sperm-ducts 
and the prostatic lobes (yesicula prostatica). 

The internal sexual organs in Mammals undergo very 
peculiar modifications in point of position. At first the 
germ-glands, in both sexes, lie deep down in the ventral 
cavity, on the inner side of the primitive kidneys (Figs. 
320, g, 321, k), attached to the vertebral column by a short 
mesentery (in the male, the mesorchium ; in the female, 
viesovarium). It is only, however, in Monotremes that this 
original position of the germ-glands is (as in lower Verte- 
tebrates) permanent. In all other Mammals (Marsupials as 
well as Placentals) these glands quit their place of origin 
and make their way more or less downward (or towards the 
posterior extremity), following the course of a cord which 
extends from the primitive kidney to the groin region of 
the abdominal waU. This is the groin-cord of the primitive 
kidney; in the male, the "Hunterian guiding-cord" (^vher- 



420 



THE EVOLUTION OF MAN, 



naculum testis) (Fig. 328, M, gh) ; in the female, the round 
uterus-cord (Fig. 328, F,t). In the latter the ovaries 
migrate more or less in the direction of the small pelvis, or 



^A.. 



. 9h 



n- A 





Fig. 328, M. 



Fig. 328, F. 



Fig. 328. — Original position of the sexual glands in the abdominal cavity 
of the human embryo (of three months). Fig. 328, M, male (natural size) : 
h, testis ; gh, the conducting-cord of the testis ; wg, seed-duct ; h, urinary 
bladder ; uh, lower hollow vein (vena ca/od) ; nn, supplementary kidneys ; 
n, kidneys. Fig. 328 F, female (somewhat enlarged) : r, I'ound uterus-cord 
(below this the urine-bladder, above it the ovary) ; r', kidney ; s, sup- 
plementary kidney ; c, blind-intestine {caecum) ; o, small net ; om, large 
net (between the two is the stomach) ; Z, spleen. (After Kolliker.) 

even enter this. In the male the testis quits the abdominaj 
cavity altogether, passing through the groin-canal, and 
enters a sac-shaped, distended fold of the external skin- 
covering. The coalescence of the right and left folds 
(" sexual folds ") gives rise to the testis-sac {scrotum).. The 
various Mammals exhibit the various stages of this migra- 
tion. In the Elephant and in Whales the testes descend 
very little, and lie below the kidneys. In many Gnawing- 
Animals (Rodentia) and Beasts of Prey (Carnaria) they 
enter the groin-canal. In most higher Mammals they pass 
down through this into the testis-sac ; usually the walls of 



EXTERNAL SEXUAL OROAWfik 421 

the groin-canal coalesce. When, however, this remains 
open, the testes are able to descend periodically (in the rutting 
season) into the testis-sac, returning again into the abdo- 
minal cavity {e.g., in Pouched Animals or Marsupialia, 
Gnawing Animals, Bats, etc.). 

Another peculiarity of Mammals is the formation of the 
external sexual organs which, as copulative organs, serve 
to carry the fertilizing sperm from the male into the 
female organism in the act of copulation. Organs of this 
sort are altogether wanting in most lower Vertebrates. In 
those which are aquatic (e.g., Acrania, Cyclostoma, and most 
Fishes) the eggs and sperm are simply discharged into the 
water, and their coming together is the result of some lucky 
accident which in this way brings about impregnation. On 
the other hand, in many Fishes and Amphibia which bring 
forth their young alive, there is a direct transfer of the 
sperm from the male to the female orgauism ; and this is 
the case in all Amniota (Reptiles, Birds, and Mammals). In 
these animals the urinary and genital organs always open 
originally into the lower part of the rectum, which thus 
forms a " cloaca " (p. 345) ; but among Mammals the cloaca 
is permanent only in the Beaked Animals (Ornithostoma) , 
which have, on this account, been called Cloacal Animals 
{Monotrema, Fig. 327, cl). In all other Mammals a lateral 
partition wall develops in the cloaca (in the human embryo 
about the middle of the third month), by which the latter 
is separated into two cavities The urinary sexual canal 
passes into the anterior cavity (sinus urogenitalis), and it 
is through this cavity alone that the urinary and sexual 
products are discharged, while the *' anal cavity," which lies 
behind it, serves merely to eject the excrement through the 



422 



THE EVOLUTION OF MAN. 



anus. Even before the appearance of this partition, in the 
Pouched Animals (Marsupialia) and Placental Animals, a 
conical papilla — the sexual protuberance (phallus, Fig. 329, 
A,e, JB, e) — rises on the anterior part of the circumference of 




^- Ji 



i. 




1^1 




B. 

Fig. 329. — External sexual organs of the human embryo : A, neutral 
germ (in the eighth week ; twice the natural size ; with cloaca) ; B, neutral 
germ (in the ninth week ; twice the natural size ; anus distinct from the 
urogenital opening) ; C, female germ in the eleventh week ; D, male germ 
in the fourteenth week ; e, sexual protuberance (phallus') ; /, sexual furrow ; 
hi, sexual folds ; r, Raphe (point of union of the penis and scrotum) ; 
a, anus; ug, urinary sexual opening; n, navel-cord; s, tail. (After Ecker.) 
Cf. Table XLIV., p. 431. 



the cloaca-opening. The apex of this is swollen into a knob 
(the " acorn," glans). On the under side appears a furrow 
(sulcus genitalis, f), and on each side of the latter a skin- 
fold, or sexual fold (hi). The phallus is especially the organ 
of the " sexual sense," and over it are distributed the sexual 



FALSE HERMAPHRODITISM. 423 

nerves (nervi pudendi) which are especially concerned in 
producing the sexual sensations (p. 238). In the male the 
phallus develops into the masculine "penis" (Fig. 329, D, «); 
in the female it becomes the much smaller " clitoris " (Fig. 
329, 0, e) ; only in some Apes {Ateles) does this become im- 
usually large. The " fore-skin " (prcBputiv/m), in both 
sexes, also develops as a skin-fold from the anterior part of 
the circumference of the phallus. In the male sexual furrow 
the lower side of the phaUus receives the urogenital 
canal, and, as a continuation of the latter, modifies, by the 
coalescence of its two parallel edges, into a closed canal — 
the male urinary tube (urethra). In the female this occurs 
only in a few instances (in some Semi-apes, Gnawing Animals 
or Rodentia, and Moles) ; as a rule the sexual furrow remains 
open and its edges are developed into the labia minora. 
The labia majora of the female develops from the two 
parallel skin-folds which appear on each side of the sexual 
furrow. In the male these last folds coalesce, forming a 
closed sac, the testis-sac (scrotum). Occasionally this 
coalescence does not take place, and the sexual furrow also 
sometimes remains open (hypospadia). In these cases the 
external male genitalia resemble the female, and this phe- 
nomenon has often been mistaken for hermaphroditism 
(pseudo-hermaphroditism).^^' 

From this and other cases of false "hermaphroditism," 
the much less frequent cases of "true hermaphroditism" are 
very distinct. This exists only when the essential organs of 
reproduction, both kinds of germ-glands, are united in one 
individual. Either an ovary is then developed on the right, 
and a testis on the left (or vice versa) ; or testes and ovaries 
are developed on both sides, one more, the other less 



424 THE EVOLUTION OF MAN. 

perfectly. As we have already seen that the original 
rudiment of the sexual organs is really hermaphroditic in 
all Vertebrates, and that the separation of the sexes is only 
due to a one-sided development of this hermaphroditic 
rudiment, these remarkable cases offer no theoretic diffi- 
culties. They very seldom, however, occur in Man and the 
higher Vertebrates. On the other hand, we find original 
hermaphroditism constant in some lower Vertebrates, as in 
some Fishes of the Perch kind (Serranus), and in some 
Amphibia {Bombinator and in Toads). In these cases, the 
male has usually a rudimentary ovary at the upper ex- 
tremity of the testis ; on the other hand, the female has 
sometimes a rudimentary testis, without function. This 
also occurs occasionally in Carp and some other Fishes. 
We have already seen how the original hermaphroditism 
is maintained in the excretory ducts, in Amphibia. 

In the germ-history of the human urinary and sexual 
organs, the outlines of the history of human descent have 
been faithfully maintained up to the present time. We can 
trace their development in the human embryo step by step 
in the same gradations as are exhibited, one after another, 
in the comparison of the urogenitals in Acrania, Cyclostomi, 
Fishes, Amphibians, and then further, in the series of 
Mammals, in Cloacal Animals {Monotr ernes). Pouched 
Animals (Marsupialia), and the various Placental Animals. 
(Cf Table XLIII.) Ail the structural peculiarities of the 
urogenitals, distinguishing Mammals from other Verte- 
brates, are also present in Man ; and in all special charac- 
teristics the latter resembles the Apes, and especially the 
Anthropoid Apes. As eviaence that the special peculiarities 
of Mammals have been transmitted to Man, I will finally 



FORMATION OF ♦THE EOOa 42$ 

briefly notice the similar manner in which the eggs are 
formed in the ovary. In all Mammals, the mature eggs are 
contained in peculiar vesicles, which, after their discoverer, 
Regner De Graaf (1677), are called the Graafian follicles. 
These were formerly regarded as the actual eggs, which 
were, however, discovered by Baer within the Graafian 
foUicles (vol. i. p. 55). Each foUicle (Fig. 330, G) consists of a 
round, fibrous capsule, which contains fluid and is coated by 
several layers of cells. At one point this cellular layer has 
a knob-like enlargement (C, 6), and, there, surrounds the 
real Qgg {C, a). The mammalian ovary is, originally, a very 
simple oblong Kttle body (Fig. 320, g), formed only of 
connective tissue, and blood-vessels, and surrounded by a 
cell-layer (the epithelium of the ovary, or the female germ- 
epithelium). From this epithelium, cords of cells grow 
inward, into the connective tissue or " stroma " of the 
ovary (Fig. 330, A, h). "Single cells of these cords increase 
in size and become egg-cells (primitive eggs. A, c); but the 
Laeater number of the cells remain small and form an 
enveloping and nutritive cellular layer (the follicle-epi- 
thelium) round each egg. 

In Mammals the follicle-epithelium is at first one- 
layered (Fig. 330, B, 1), afterwards many-layered (5, 2). In 
all other Vertebrates, the egg-ceU is, indeed, enclosed in a 
permanent covering of small cells, an egg-follicle ; but only 
in Mammals does fluid accumulate between the growing 
follicle-cells, and thus extends the follicle into a round 
bladder of considerable size, on the inner wall of which 
the egg lies excentrically. In this point, as in his whole 
Morphology, Man unmistakably indicates his descen+j firom 
Mammal& 



426 



THE EVOLUTION OF ]\LA.N. 






Fig. 330, B. 




Fig. 330, C. 



HISTORICAL IMPORTANCE OF THE SEXUAL ORGANS. 427 

Fig. 880. — Derelopment of human ovules within the female orary. — A. 
Vertical section through the ovary of a new-bom female : a, epithelium of 
the ovary ; h, rudiment of an egg-cord ; c, young eggs in the epithelium ; 
d, longer egg-cord with the follicles ; e, group of young follicles ; /, single 
young follicle ; g, blood-vessels in the connective tissue (stroma) of the 
ovary. In the cords the young primitive eggs can be distinguished from 
the Burronnding cells of the follicle by their relatively large size. (After 
Waldeyer). — 330, B. Two young follicles isolated;* in 1, the cells of the 
follicle form but a single layer around the young primitive egg ; in 2, they 
torai a double layer j in 2, they begin to form the primary chorion (a), or 
the «ona pelUtcida (vol. i. p. 135) . — 330, C. A mature human Graafian follicle : 
a, the mature egg ; h, the surrounding follicle-cells ; c, the epithelial cells of 
the follicle ; d, the fibrous membrane of the follicle ; «, its outer surface. 

The entire natural history of the human sexual organs 
is one of the branches of Anthropology which affords the 
strongest proofs of the origin of the human race from the 
animal kingdom. Each man, on knowing the pertinent 
facts, and without prejudice, judging these comparatively, 
can but be convinced that he is descended from lower 
Vertebrates. The general, and the more minute structure, 
the activity and the individual evolution of the sexual * 
organs, is exactly the same in Man as in Apes. This is as 
true of the male as of the female, of the internal as of the 
external genitalia. The differences in this matter between 
Man and the most man-like Apes are far less than the 
differences between the various forms of Apes. As, how- 
ever, all Apes are undoubtedly from a common origin, this 
fact alone proves, with absolute certainty, the descent of 
Man from Apes. 



( 428 ) 

TABLE XLIII. 

Ststkmatio BtmvBT of the most Important Periods ih thb Prtloobn) 
OF THE Urinary and Sexual Organs of Man.^*' 

XLin. A. First main diTision : the BexuiU organs (G) and the arinary 
organs (U) are distinct. (The seznal or genital system (G) and th« 
excretory or urinary system act independently of each other.) 

I. First Period : OenitaU a/ad Kidneys of OastrcBads. 

Q. Single, scattered cells of the entoderm change into egg-oeHs ; single, 
scattered cells of the exoderm into sperm-oells. 

U. Special arinary organs are as yet wholly waiting. Seoretrai i» 
performed by the cells of the exoderm. 

IL Second Period : Genitals and Kidmeys of Primitive Worms, 

G. The egg-cells of the entoderm gather into groups (ovary.plates) ; as 
do the sperm-cells of the exoderm (testis. plates). 

U. A pair of simple pouch-like skin-glands (products of the skin-sensory 
layer) develop into extremely simple kidney-canals (excretory organs of the 
Plat-worms, Platelminthes). 

III. Third Period : Genitals and Kidneys of Scotedda, *" 

Q. After the differentiation of the four secondary germ-layers is com. 
plete, the egg-cells pass from the skin-sensory layer into the skin-fibrous 
layer ; the sperm-cells also pass from the intestinal-glandular layer into the 
intestinal -fibrous layer. 

U. After the formation of the coelom is completed, the blind inner ends 
of the two kidney •canals (or *' primitive kidney ducts ") open into the body- 
cavity (eoslotna). 

rV. Fourth Period : Genitals amd Kidm.eys of Chordonia. 

0. The groups of egg-cells (ovarial plates) and the groups of sperm-ceHi 
(testes-plates) meet at the boundary between the endocoelar (the visceral 
intostinal-fibrous layer of the coelom-epithelium) and the exocoelar (the 
parietal skin-fibrous layer of the coelom-epithelium), so as to form the 
hermaphrodite glands. 

T7. The primitive kidney ducts differentiate into an excretory and • 
glandular pari. 

V. Fifth Period : Genitals a/nd Kidneys of Aerania. 

O. The sexes become distinct. In the female, only the ovary m de- 
raloped ; in the male, only the testes. 

XJ. The primitive kidney ducts remaan simple (atrophied in Atnphioausy 



PHYLOGENY OF URINARY AND SEXUAL OROANa 429 

TI. Sixth Period : Oenitals amd Kidney $ of Cyclostom: 

G.. The seraal glands (nomerons in Acrania) coalesce into a p&ir. 

U. The primitive kidney ducts send out lateral branches which acquire 
rascular ooils (glomeruli) (the semi-pinnate primitiye kidneys of BdeUo- 
stomtk). 

XLIII. B. Second main diyision : the genital organs (G) and tiie vrixuurj 
organs (U) become united. (The sexual system and the urinary system 
are united in the " urogenital system.") 

VII. Seventh Period : Urogenitals of Primitive Pishes (SeUiehii). 

The primary primitive kidney duct differentiates on each side, f(wrming 
two secondary canals ; the Wolffian duct, which develops into the seed-duct, 
and the Miillerian duct, which develops into the oviduct. Both genital 
doots originally open behind the anus (JProselachii). 

VIII. Eighth Period : Urogenitals of Dipneusta, 

A cloaca is formed by the union of the urogenital opening and the cavity 
of the anus. The single urinary bladder grows out from the anterior wall of 
the rectum (Lepidosiren). 

IX. Ninth Period : Urogenitals of Amphibia, 

Prom the uppermost part of the primitive kidney which is in process of 
atrophy, proceeds, in the male sex, the supplementary testis ; in the female 
sex, the supplementary ovary. The Wolffian duct yet acts, in both sexes, an 
a urinary canal, and, in the male, also as the seed-duct. The MiilleriaD 
duct acts in the female sex as oviduct ; in the male it is a radimentar^ 
organ (Bathke's duct). 

X. Tenth Period : Urogenitals of ProtamiUm. 

Hie atrophied primitive kidney is replaced by the permanent seoondary 
kidney as the urinary organ. The urinary bladder grows out from the 
ventral orifice of the embryo and fuM-ms the allantois. From the anterior 
wall of the cloaca grows the sexual protuberance (phaUiks), whlok, in the 
male, develops to the penis, in the female, to the clitoriB. 

I 

XI. Eleventh Period : Urogenitals of MonoWemse* 

Tbe lower end of the oviduct enlarges on each side to % mafcnlar 
atema. 

XII. Twelfth Period : Urogenitals of lfar«i(piaZ««. 

The cloaca is separated by a partition into an anteri(»: urogenitftl opening 
%pertura Mrogenitalis) and a posterior anal opening (onta). Fron the 



430 THE EVOLUTION OP MAW. 

low«r part of the nteras the ragina. canal passes ont on each tide. Ae 
oyarieB and testes begin to move downward from their place of formation. 

XIII. Thirteenth Period : Urogenitals of 8em%.a/pe», 

The lower parts of the Miillerian and the Wolffian dncts ooalesee into 
a sexual cord. The coalescence of the two uteri at the lower part gives 
riie to the uterus hicomia. A part of the allantois becomes the plaoenta. 

XIV. Fourteenth Period : Urogenitals of Apes. 

The two uteri coalesce throughout their entire length, forming a single 
pear-shaped uterus, as in Man. 



A 



( 431 ) 



TABLE XLIV. 

Sjatematic Sorrej of the Homologies of the Sexual OrgaoB in the tyro 8«zea 

of Mammals. 



XLIV. A. Homologies op the Internal Sexual OKOAKt. 



9. CiNMmon Rtidimentt of tk» 
iHUmai StxiMl Organt. 


M. JnUmdl Male Parta. 


F. Interttcu Ikatait PmrU. 


1. 


Male germ -gland (testes-plate 


1. Testis 


1. Rndimentary testlB dis- 




in the •mbryo, product of the 


(TettU, or OrchU) 


appears,— remaina in 




•kin-layer ?) 




some AmphlbiA 


i. 


Female germ-gland (ovary-plate, 


2. (Rudimentary ovary, dis- 


2. Ovary 




product of the intestinal 


appears, — remains in 


(Ovarium, or Oopkoron) 




layer ?) 


some Amphibia) 




5. 


WolfBan duct (lateral primitive 


3. Seed-duct 


3. Oartnerlan dxict (rndi- 




kidney duct) 


( S[>e rmadiLctuM) 


mentary eaoal) 


* a. Miillerian duct 


4*. Kathke'8 duct (rodi- 


4 a. Oviduct 




(Ductus MiilUri, central pri- 


mentary canal io 


(Oviductut, n M>a 




mitive kidney duct) 


Amphibia) 


Fallopice) 


4 6. Upper part of the Mailerlan 


4 h. Hydatit Morgagni 


4 b. Hydatit FaM«f%a 


4 c. Lower part •f the Miillerian 


4 e. rterut maicuXxnut 


4 e. Utenu, sheath (vo^tna) 




duct 


( Vesicula proitatica) 




K. 


Remnant of the primitive kidney 


5. Supplementary teste* 


6. Supplementary ovary 




(Protonephron, corput Wolf- 


(EpididymU) 


(Parovarium) 


6. 


JIX) 

Groin ligament of the primitive 


%. Honterian guiding-cord 


9. Bound utenu-oord 




kidney 


CGubemacuium S*m- 


(Ligamentum uteri 




{Ligamentymk protonephroiW' 


Uri) 


rotundum) 




guinale) 






7. 


Sexual mesentery 


7. Testis-mesentery 


7. Ovary -mesoitery 




(JiesenUrium sexudU) 


(^Mesorchium) 


(Jtet9varivm) 



XLIV. B. Homologies oi the External Sexual Oboans. 



9. Otmmon Rudiments of the 
WKtemal Sexual Organs. 


M. External Male Parts. 


F. External Female FturU. 


t. Sexual protaberaooe 
(PhaUus) 

t. Fore-skin 


8. Penis 

t. Male fore-skin 


t. OitOTii 

9. Female fore-sUn 


(Prceputiutm) 

10. Sexual folds 

(Plica genitaUs') 

11. FlMure between tne two sexual 


(Praputium penit) 

10. Testes-sac 

(Scrotum) 

11. Seam of the testis-sae 


(Prceputium ditoridis) 
19. I^iapudendiwu^joret 

11. FeaiAle FkIm 


folds 
12. Sexual edges (edges «f the 
sexual furrow) 


(Raphe scroti) 
12. Edges of the sexual 
furrow coalesce 


12. Labia pudendi m imer% 


la. Urogenital canal 

(Sinus urogenitalis) 
14. Qlandular appendages of Um 


13. Ureters 

(Urethra) 

14. Cowper's glands 


13.Antechamber of the vac&u 

( \est\bul%im vagimm) 
U. Bartboli's gl«B^ 



61 



CHAPTER XXVI. 

RESULTS OF ANTHROPOGENY. 

Review of the Germ-history as given. — Its Explanation by the Fundamental 
Law of Biogeny. — Its Cansed Rel&tion to the History of the Tribe. — 
Rudimentary Organs of Man. — Dysteleology, or the Doctrine of Pur- 
poselessness. — Inheritances from Apes. — Man's Place in the Natural 
System of the Animal Kingdom.— Man as a Vertebrate and a Mammal. 
— Special Tribal Relation of Men and Apes. — Evidences regarding the 
Ape Question. — The Catarhina and the Platyrhina. — The Divine Origin 
of Man. — Adam and Eve. — History of the Evolution of the Mind. — 
Important Mental Differences within a Single Class of Animals. — The 
Mammalian Mind and the Insect Mind. — Mind in the Ant and in the 
Scale-louse (Cocctw). — Mind in Man and in Ape. — The Organ of Mentui 
Activity : the Central Nervous System. — The Ontogeny and Phy. 
logenj of the Mind. — The Monistic and Dualistic Theories of the 
Mind. — Heredity of the Mind. — Bearing of the Fundamental Law of 
Biogeny on Psychology. — Influence of Anthropogeny on the Victory of 
the Monistic Philosophy and the Defeat of the Dualistic. — Nature and 
Spirit. — Natural Science and Spiritual Science. — Conception of the 
World reformed by Anthropogeny. 

" The Theory of Descent is a general inductive law which results with 
absolute necessity from the comparative synthesis of all the phenomena of 
organio nature, and especially from the threefold parallel of phylogenetio, 
ontogenetic, and systematic evolution. The doctrine that man has de- 
veloped from lower Vertebrates, and immedately from genuine Apes, is 
a special deductive conclusion, which results with absolute necessity from 
the general inductive law of the Theory of Descent. This view of ' man's 



SUMMARY. 433 

place in natnre,* oftnnot, we believe, be made too prominent. If the Theorv 
of Descent is correct as a whole, then the theory that man has developed 
from lower Vertebrates is simply an unavoidable deductive conclusion fruui 
that general inductive law. Hence, all farther discoveries which may ii) 
future enrich our knowledge of the phyletic development of man, can only 
be confirmative of special points of that deduction, which resta on the 
broadest inductive basis." — Qenerelle Morphologie (1866). 

As we have now traversed the wonderful territory of 

the history of human development, and learned its mo^f 
important parts, it seems appropriate that, at the close of 
our travels, we should look back on the road behind us, 
and, on the other hand, glance forward along the further 
path of knowledge into which our road will lead in future. 
We started from the simplest facts of the history of man's 
individual development; ontogenetic facts which can, at 
any moment, be shown and established by microscopic or 
anatomic research. The first and most important of these 
ontogenetic facts is, that every man, like every other 
animal, is at the commencement of his individual existence, 
a simple cell. This egg-cell exhibits precisely the same 
structure and mode of origin as that of any other Mammal. 
From this cell proceeds, by repeated division, a many-celled 
body, the mulberry-germ (morula); this changes into a 
cup-germ (gastrula), and this, again, into an intestinal 
germ-vesicle (yastrocystis). The two distinct cell-strata 
which compose its wall are the two primary germ- 
layers ; the skin-layer (cxoderrrui) and the intestinal layer 
(entoderma). This double-layered germ-form is the onto- 
genetic reproduction of that extremely important phylo- 
genetic parent-form of all Intestinal Animals, to which we 
have given the name Gastrsea. 

As the human germ, like that of other Intestinal Animals, 



4.34 THE EVOLUTION OF MAN. 

passes through this gastrula-form, we are enabled to trace 
its phylogenetic origin back to the Gastrsea. By tracing the 
germ-history of the two-layered germ still farther, we found 
that, by fission, four secondary layers are produced from 
the two original germ-layers. These have exactly the same 
constitution and genetic significance in Man as in all other 
Vertebrates. From the skin-sensory layer develops the 
outer skin (epidermis) and the central nervous system, and, 
probably, the kidney system. The skin-fibrous layer forms 
the leather-skin (corium) and the organs of motion (the 
skeleton and muscle systems). From the intestinal-fibrous 
layer originates the vascular system and the fleshy wall of 
the intestine. The intestinal-glandular layer, finally, forms 
only the epithelium, or the inner cellular layer of the 
intestinal-mucous membrane and of the intestinal glands. 

The manner in which these various organic systems 
develop from the four secondary germ-layers, is, from the 
very first, exactly the same in Man as in all other Verte- 
brates. The germ-history of each separate organ afibrded 
proof that the human embryo takes exactly the same special 
direction in its difierentiation and formation, which, except 
in Man, occurs only in the other Vertebrates. Within this 
great animal tribe we then traced, step by step, and stage 
ofber stage, the farther development which takes place in the 
entire body as well as in all its several parts. This higher 
development takes place in the human embryo in the form 
peculiar to Mammals. Finally, we saw, that even within 
this class the various stages of phylogenetic development, 
which determine the natural classification of Mammals, 
correspond throughout to the various stages of ontogenetic 
formation through which the human embryo passes in the 



rUNDAMENTiX LAW OF BIOQENt. 435 

further course of its development. We were thus enabled 
to determine the place of Man more definitely in the system 
of this class, and accordingly to establish the nature of his 
relation to the various mammalian orders. 

The course of reasoning which we adopted in explaining 
these ontogenetic facts, was simply the logical carrying out 
of the fundamental law of Biogeny. In so doing we have 
constantly tried to carry out the significant distinction 
between palingenetic and kenogenetic phenomena. Palin- 
genesis, or "the history of inheritance," alone enabled us to 
draw direct conclusions from observed germ-forms as to the 
tribal forms transmitted by heredity. On the other hand, 
these conclusions were more or less endangered, wherever 
Kenogenesis, or "vitiated evolution," was introduced by new 
adaptations. The whole understanding of the history of in- 
dividual evolution depends on the recognition of this most 
important relation. We stand here on the border-line which 
sharply divides the new from the old method of scientific 
investigation, the new from the old conception of the world. 
All the results of recent morphological research drive us 
with irresistible force to the recognition of this fundamental 
principle of Biogeny, and of its far-reaching consequences. 
These are, it is true, irreconcilable with the customary 
mythological ideas of the world, and with the powerful 
prejudices engrafted into us in early youth by theosophie 
instruction ; but, without this fundamental law of Biogeny, 
without the distinction between Palingenesis and Keno- 
genesis, and without the Theory of Descent, upon which 
these are based, we are entirely unable to understand the 
facts of organic development ; without these, we cannot 
afford the faintest explanation of any part of this great and 



436 THE EVOLUTION OF MAH. 

wonderful world of phenomena. But, if we recognize the 
causal relation between the development of the germ and 
that of the tribe, if we recognize the true causal connection 
of Ontogeny and Phylogeny, which is expressed in that law, 
then the wonderful phenomena of Ontogeny explain them- 
selves most simply; then the facts of germ-development 
appear but the necessary mechanical effects of the develop- 
ment of the tribe, conditioned by the laws of Heredity and 
Adaptation. The inter-operation of these laws among the 
everywhere-active influences of the struggle for existence, 
— or, as we may simply say with Darwin, Natural Selection, 
— is amply sufficient to explain to us the entire process of 
germ-history by the history of the tribe. Darwin's chief 
merit lies in the fact, thait by the discovery of the inter- 
action of the phenomena of Heredity and Adaptation, he 
prepared the way for a correct, logical understanding of the 
history of Evolution. 

Among the numerous and important evidences that we 
have found for the truth of this view of our development 
history, I will only call attention here once more to the 
peculiarly valuable records of creation afforded by Dystele- 
ology, or the doctrine of purposelessness, the science dealing 
with rudimentary organs. It is impossible to emphasize 
too often and too strongly the high morphological import- 
ance of those remarkable parts of the body, which are, 
physiologically, completely worthless and useless. In every 
system of organs we find, in Man and in all higher Verte- 
brates, some of these worthless primaeval heirlooms, which 
have been inherited from our lower vertebrate ancestors. 
Thus, first, we find on the outer surface of the body a scanty 
rudimentary covering of hair, which is thicker only on the 



1 



BITDIMENTAIIT OEGANS. 43/ 

head, in the armpits, and on some other parts of the body. The 
short hairs on the greater part of the surface of our bodies are 
entirely useless, are without any physiological significance ; 
they are the last scanty remains of the much more fully 
developed haiiy covering of our Ape ancestors (p. 208). The 
sense-organs exhibit a series of the most remarkable rudimen- 
tary parts. As we have seen, the whole external shell of the 
ear, with its cartilages, muscles, and membranes, is, in Man, 
a useless appendage, destitute of the physiological importance 
that was formerly, erroneously, attributed to it It is the 
atrophied remnant of the pointed, freely-moving, and much 
more highly developed mammalian ear, the muscles of which 
we retain, although we can no longer use them (p. 271). 
Again, we found, at the inner comer of the human eye, the 
remarkable little crescent-shaped fold, which is of no use to 
us, and is of interest only as being the last vestige of the 
nictitating membrane ; of that third inner eyelid which is 
still of great physiological importance in Sharks and many 
Amnion Animals (p. 259). Numerous and interesting 
dysteleological proofs are also afforded by the apparatus of 
motion, both by the bony and the muscular systems. I 
will only cite the free, projecting tail of the human embryo, 
and the rudimentary caudal vertebrae developed in the 
latter, together with the pertinent muscles ; this whole 
organ is entirely useless to Man, but is of great interest as 
the atrophied remnant of the long tail of our earlier Ape 
ancestors, which was composed of numerous vertebrae and 
muscles (p. 283), From these same ancestors we have also 
inhtrited various bone-processes and muscles, which were of 
great use to them in their climbing life among the trees, but 
with us have fallen out of use. At various points under the 



433 THE EVOLUTION OF MAN. 

skill we also have entirely unused skin-muscles ; vestiges of 
the largely developed skin-muscles of our lower mam- 
malian ancestors. It was the function of this " panniculus 
camosus " to contract and wrinkle the skin, as we may see 
any day done by horses to drive away flies. We still 
possess an active remnant of this great skin-muscle in the 
muscle of the forehead, by means of which we wrinkle the 
forehead and draw up the eyebrows ; but we are no longer 
able to move at will another considerable remnant of it, the 
great skin-muscle of the neck (platysma myoides). 

As in these animal organ-systems of our body, so also in 
the vegetative apparatus, we meet with many rudimentary 
organs, most of which we have incidentally noticed. I will 
only cite the remarkable thyroid gland (thyreoidea), the 
rudiment of the crop and the remnant of the ciliated groove 
(hypobranchial groove) present in Chordonia, Ascidia, and 
Arcrania, on the lower part of the gill-body (pp. 336, 353) ; 
also the vermiform process of the blind-intestine (ccscwm) 
(p. 344)). In the vascular system we find many useless 
ducts, the vestiges of disused vessels which were formerly 
active blood-channels ; such, for instance, are the " ductus 
BotaUi" between the lung-artery and the aorta, and 
the ** ductus venosua Arantii*' between the vena portce 
and vena cava, and many others. The numerous rudi- 
mentary organs of the urinary and sexual systems (p. 415) 
ar© especially interesting. Most of these are developed in 
on© sex and rudimentary in the other. Thus, in the male, 
the seed-ducts form from the Wolffian ducts, of which the 
only traces remaining in the female are the Gartnerian 
canals. On the other hand, from the Miillerian ducts in the 
female are developed the oviducts and the uterus ; while io 



HISTORICAL IMPORTANCE OF THE RUDI^HENTARY ORGANS. 439 

the male, only the lower extremities of these ducts remain, 
forming the useless male uterus (vesicula prostatica). In 
the nipples and mammary glands, the male possesses other 
rudimentary organs which, as a rule, are functional only in 
the female (p. 204). 

A closer anatomical examination of the human body 
would bring to our notice a number of other rudimentary 
organs, aU of which can be explained only by the Theory of 
Descent. They are among the most important evidences foi' 
the truth of the mechanical theory of nature, and among the 
most overwhelming proofs against the prevailing teleologica] 
ideas of creation. If, in accordance with this latter view, Man 
and every other organism had been designed for his life- 
purpose from the beginning, and had been called into existence 
by an act of creation, the existence of these rudimentary 
organs would be an incomprehensible enigma ; it would be 
impossible to understand why the Creator should have laid 
this useless burden on his creatures in their life-journey, so 
arduous at the best. On the other hand, by means of the 
Theory of Descent we can explain their existence in the 
most simple way, and say : The rudimentary organs arc 
parts of the body, which, in the course of centuries, 
have gradually fallen out of use ; organs which perfoimed 
definite functions in our animal ancestors, but which, in 
lis, have lost their physiological importance. They have 
become useless in consequence of our adaptation to new 
circumstances, but yet are transmitted from generation to 
generation by heredity, and have only slowly atrophied. 

Like these rudimentary organs, so also all the other 
organs of oui body have been transmitted to us from 
Mammals, and, immediately, from our Ape ancestors. The 



440 THE EVOLUTION OF MA2f. 

iiiiman body includes no single organ which is not in- 
licrited from Apes ; but, by means of our fundamental law 
of Biogeny, we can trace the origin of our several systems 
of organs yet further down to various lower ancestral 
grades. Thus, for instance, we can say that we have 
inherited the earliest organs of our body, the outer-skin 
(epidermis) and the intestinal canal, from the Gastraeads, 
the nervous and muscular systems from the lower Worms 
{Archelminthes), the vascular system, body-cavity (cceloma), 
and blood from Soft Worms (Scolecida), the notochord and 
the gill-intestine from Chorda Animals, the differentiated 
organs of sense from the Cyclostoma, the limbs and the 
Miillerian ducts from Primitive Fishes (Selachii), and the ex- 
ternal reproductive organs from Primitive Mammals (Pro- 
niammalia). When we stated the " law of the ontogenetic 
connection of systematically allied forms," and determined 
the relative age of the organs, we saw how we could draw 
such phylogenetic conclusions as these from the ontogenetic 
succession of the organ-systems (vol. i. p. 390 ; ii, 357). 

By the help of this important law and of Comparative 
Anatomy, we were also enabled to determine definitely 
"man's place in nature," or, as we may say, to assign to 
man his position in the system of the animal kingdom. It 
is now usual, in the more recent zoological systems, to 
distribute the whole animal kingdom into the seven tribeS; 
or phyla, which are again sub-divided, in round numbers^ 
into about forty classes ; and these classes into about 
two hundred orders. According to his whole organization, 
Man is undoubtedly, primarily, a member of but a single 
tribe, that of Vertebrates ; secondly, he is a member of but 
a single class, that of Mammals ; and, thirdly, a membei 



"man's place in nature.*' 441 

of but a single order, that of the Apes. All the character 
istic peculiarities, distinguishing Vertebrates from the other 
six tribes, distinguishing Mammals from the other forty 
classes, and distinguishing Apes from the remaining twro 
hundred orders of the animal kingdom, are also present 
in Man. Turn and twist as we may, we cannot escape thii3 
anatomical and systematic fact. Quite recently this very 
fact has led to the liveliest discussion, and has occasioned, 
especially, many disputes about the specific anatomical 
relationship of Man to Apes. The most astounding views 
on this "ape question," or "pithecoid theory," have been 
uttered. It will therefore be well to examine it closely 
once more at this point, and to separate the essential from 
the non-essential in it. 

We will start from the undisputed fact, that Man, at all 
events, — whether his special blood-relationship to Apes is 
acknowledged or denied, — is a genuine Mammal, is a Pla- 
cental Mammal. This fundamental truth can be so easily 
proved at any moment by investigations in Comparative 
Anatomy, that it has been unanimously acknowledged since 
the separation of the Placental from the lower Mammals 
fPouched Animals, or Marsupialia, and Beaked Animals, or 
Ornithostoma). But, from this, every logical adherent of 
the doctrine of development at once draws the conclusion, 
that man is descended from one and the same common 
parent-form, together with all other Placental Animals, from 
the progenitor of the Placentalia, just as, further, we must 
necessarily suppose a common mammalian ancestral form 
of all the various Mammals (Placentalia), Pouched Animals, 
and Cloacal Animals (Monotremata) ; but by this the grea/., 
all-agitatiog main question of man's place in nature is 



442 THE EVOLUTION OP MAN. 

conclusively settled, whether we ascribe to Man a nearer ot 
a more remote relationship to Apes. No matter whether 
Man is, in a phylogenetic sense, a member of the Ape order 
(or, if it is preferred, of the Primate order) or not, — in 
any case, his direct blood-relationship to all other Mammals, 
and especially to the Placental Mammals, is established. It 
may be that the inter-relations of the various Mammals 
are quite different from those now hypothetically assumed ; 
but, in any case, the common descent of Man and all 
other Mammals from a common parent-forin is indis- 
putable. This primaeval, long since extinct parent-form, 
which probably developed during the Triassic Period, was 
the monotreme ancestral form of all Mammals. 

If this fundamental and extremely significant principle 
is borne in mind, the " ape question " will appear to us 
in a wholly different light from that in which it is usually 
presented. A little reflection will bring conviction that 
this question has not the importance that has of late been 
attributed to it ; for the origin of the human race from 
a series of various mammalian ancestors, and the historical 
development of the latter from an earlier series of lower 
vertebrate ancestors, remains indubitably established, no 
matter whether the genuine " Apes " are regarded as the 
nearest animal ancestors of the human race or not. But, 
it having become habitual to lay the principal weight of 
the entire question of the origin of man on this very 
*• descent from Apes," I find myself compelled to return 
once more to it here, and to recall those facts in Com- 
parative Anatomy and Ontogeny, which conclusively setth 
this " ape question." 

The shortest way to the goal is the one taken by 



t€ 



HUXLEY'S LAW/ 443 



Huxley in his celebrated work, which we have eo often 
quoted, on the " Evidences as to Man's Place in Nature/' — 
the way afforded by Comparative Anatomy and Ontogeny. 
We have to compare objectively all the several organs of 
Man with the same organs in the higher Apes, and then to 
ascertain whether the differences between the former and 
the latter are greater than the corresponding differences 
between the higher and lower Apes. The indubitable and 
indisputable result of this comparative anatomical investi- 
gation which was conducted with the greatest candour and 
accuracy, was the important law, which, in honour of its 
discoverer, we have named Huodey's Law ; namely, that the 
physical differences between the organization of Man and 
that of the most highly developed Apes known to us, are 
much smaller than the corresponding differences between 
the higher and lower Apes. We might even define this law 
yet more exactly by excluding entirely the Platyrhina or 
American Apes as being more remote relatives, and limiting 
our comparison to the narrower circle of relatives, the 
Catarhina, or Apes of the Old World. Even within this 
small group of Mammals, we found the differences of struc- 
ture between the higher and lower Narrow-nosed Apes, for 
example between the Gorilla and the Baboon, much greater 
than the differences between these Man-like Apes and Maa 
When, in addition, we now turn to Ontogeny, and when we 
find there, according to our " law of the ontogenetic con- 
nection of systematically related forms, that the embryos of 
Man and of the Man-like Apes, are identical for a longer 
period than the embryos of the highest and of the lowest 
Apes, we are certainly obliged to bring ouisi.'lvcs, whether 
with a good or a bad grace, to acknowledge our origin from 



444 THE EVOLUTION OF MAN. 

the Ape order. From the facts exliibited by Comparative 
Ajiatomy, we can undoubtedly form in imagination an 
approximate image of the structure of our ancestors during 
the older Tertiary Period ; we may fill out the details as we 
will, yet this image will be a genuine Ape, and a true 
Catarhine. For Man has all the physical characters dis- 
tinguishing the Catyrhina from the Platyrhina. Accord- 
ingly, in the mammalian pedigree, we must derive the 
human race directly from the Catarhine group, and refer 
the origin of Man to the Old World For the entire group 
of the Catarhine Apes has, as yet, been confined to the Old 
World, just as the group of the Platyrhine Apes has been 
limited to the New. Only the earliest root-form, that from 
which both groups sprang, was common to them; probably 
it originated from the Semi-apes of the Old World. 

Therefore, although it is thus indubitably established as 
the result of our objective scientific inv^uiry, that the human 
race is directly descended from the Apes of the Old World, 
yet we will once more state emphatically that this signifi- 
cant fact is not of as great importance to the main question 
of the origin of Man, as is generally supposed. For, even 
if we entirely ignore the fact or thrust it aside, this will 
not affect all that the zoological facts of Comparative 
Anatomy and the history of development have taught us 
concerning the placental character of Man. These clearly 
prove the common descent of Man and the other Mammals. 
It is evident also, that the main question cannot be in the 
least evaded or set aside by the statement : " Man is, indeed, 
a Mammal; but he branched off from the others quite at 
the root of the class, and has no nearer relationship with 
any other extant Mammal." At all events, the relationship 



EVOLUTION AND SENTIMENT. 445 

is evidently more or less close if we comparatively examine 
the relation of the Mammalian class to the remaining forty 
classes of the animal kingdom. All Mammals, including 
Man, are, at least, of common origin, and it is equally 
certain that their common parent-forms gradually developed 
fix)m a long series of lower Vertebrates. 

Feeling, evidently, rather than understanding, induces 
most people to combat the theory of their "descent from 
Apes." It is simply because the organism of the Ape appears 
a caricature of Man, a distorted likeness of ourselves in a 
not very attractive form, because the customary aesthetic 
ideas and self-glorification of Man are touched by this in so 
sensitive a point, that most men shrink from recognizing 
their descent from Apes. It seems much pleasanter to be 
descended from a more highly developed, divine being, 
and hence, as is well knoTVTi, human vanity has, from the 
earliest times, flattered itself by assuming the original 
descent of the race from gods or demi-gods. The churcli 
with that sophistical distortion of ideas of which she i- 
so great an adept, has managed to extol this ridiculous 
pride as Christian humility ; and those people who 
reject with haughty horror every suggestion of descent 
from lower animals, and consider themselves children of 
God, those very people are exceedingly fond of boasting 
about their childlike humility of spirit. In most of the 
sermons delivered against the progress of the doctrine 
of evolution, human "vanity and conceit play throughout 
a prominent part ; and, although we have inherited this 
characteristic weakness from Apes, yet we must confess to 
having developed it to a degree of perfection which 
completely overthrows the unprejudiced judgment of the 



446 THE EVOLUTION OF MAX. 

" sound understanding of man." We ridicule th© childiBh 
follies occasioned by the pride of ancestry among the 
nobility, from the splendid Middle Ages down to our own 
time, and yet no small portion of this groundless prida 
of nobility lurks in a great majority of men. Just as most 
people prefer to trace their pedigree from a decayed baron 
or, if possible, from a celebrated prince, rather than from 
an unknown, humble peasant, so they prefer seeing the pro- 
genitor of the human race in an Adam degraded by the Fall, 
rather than in an Ape capable of higher development and 
progress. It is a matter of taste, and such genealogical 
preferences do not, therefore, admit of discussion. StiU I 
must confess that, personally, I am as proud of my paternal 
grandfather, who was simply a Silesian peasant, as of my 
maternal grandfather, who raised himself from the position 
of a Rhenish lawyer to the highest posts in the council 
of state. And it is also much more to my individual taste 
to be the more highly developed descendant of a primaeval 
Ape ancestor, who, in the struggle for existence, had de- 
veloped progressively from lower Mammals, as they from 
stUl lower Vertebrates, than the degraded descendant of 
an Adam, god-like, but debased by the Fall, who was formed 
from a dod of earth, and of an Eve, created from a rib of 
Adam. As regards this celebrated " rib," I must here ex- 
pressly add as a supplement to the history of the develop- 
ment of the skeleton, that the number of ribs is the same in 
man and in woman. In the latter as well as in tiie former, 
the ribs originate from the skin-fibrous layer, and are to be re- 
garded phy logenetically as lower or ventral vertebrae (p. 285). 
Now I certainly hear some one say : " That may all be 
right and correct as far as the human body is concerned, and, 



EVOLUTION OF THE MIND. 447 

from the facts presented, it is certainly no longer to be 
doubted that tliis has actually developed gradually, step by 
step, from the long ancestral series of Vertebrates ; but it is 
quite otherwise with the ' spirit of man,* with the human 
mind, which cannot possibly have developed in a similar 
way from the mind of lower Vertebrates." Let us see if the 
known facts of Comparative Anatomy, Physiology, and 
Evolution can meet this grave objection. We shall best 
gain firm ground from which to start in this matter by 
comparatively examining the minds of the difierent Verte- 
brates. Side by side within the various classes, orders, 
genera, and species of Vertebrates, we find so great a variety 
of vertebral intellects, that, at first sight, one can scarcely 
deem it possible that they can all be derived from the mind 
of a common " Primitive Vertebrate." First, there is the 
little Lancelet, which has no brain at all, but only a simple 
medullary tube, the entire mental capacity remaining at 
the very lowest grade occuning among Vertebrates. The 
Cyclostomi, also, standing just above, exhibit a hardly 
higher mental life, though they have a brain. Passing on to 
Fishes, we find then- intelhgence, as is well known, also 
at a very low point. Not until from these we ascend to the 
Amphibia, is any essential progress in mental de^^elopment 
observable. This is much greater in Mammals, although, 
even here, in the Beaked Animals {Ornithostoma), and the 
next higher class, the stupid Pouched Animals {Marrj/pials), 
the entire mental activity is still of a very low order ; but 
if we pass on from these to Placental Animals, within this 
multiform group we find such numerous and important 
steps in difierentiation and improvement, that the mental 
differences between the most stupid Placental Animals (for 
62 



448 THE EVOLCTTIOlf OF MAN. 

instance, Sloths and Armadillos) and the most intelligent 
animals of the same group (for instance, Dogs and Apes), 
seem much more considerable than the intellectual dif- 
ferences between those lowest Placentals and the Pouched 
Animals, or even the lower Vertebrates. Those differences 
are, at any rate, much more considerable than the dif- 
ferences in the intellectual life of dogs, apes, and men. And 
yet all these animals are allied members of a single class.^** 
This fact is shown to a yet more surprising degree in 
the Comparative Psychology of another class of animals, 
which is specially interesting for many reasons, that of 
Insects. It is well known that many Insects exhibit a 
mental capacity approximately as highly developed as is 
possessed by Man only of the vertebrate group. It is needless 
to speak of the celebrated organized communities and states 
of Bees and Ants ; every one knows that very remarkable 
social arrangements occur among these, such as occur in an 
equal degree of development only in the higher races of 
men, and nowhere else in the animal kingdom. I will only 
aUude to the civil organization and government among 
Monarchical bees and Republican ants, to their division 
into various orders : the queen, the drone nobility, the 
workers, the nurses, soldiers, and so on. Among the most 
remarkable phenomena in this extremely interesting field of 
life, is certainly the cattle-keeping of certain Ants, which 
tend plant-lice for the sake of their milk and regularly 
coUect their honey-juice. Even more remarkable is the 
slave-holding of the large red Ants, which steal the young 
of the small black species and rear them to slave-labour. 
It has long been known that all these civil and social 
arrangements of the Ants were originated by the systematic 



COMPARATIVE MENTAL CAPACITISa 449 

oo-operation of numerous citizens, understanding each other. 
Numerous observations have placed the astoundingly high 
intellectual development of these little Articulated Animab 
beyond all doubt. With this let us compare, as Darwin 
has done, the intellectual capacity of many lower, and, 
especially, of many parasitic. Insects. There, for example, 
are the Scale Insects (Coccus) which, when mature, consist 
of an entirely immovable shield-shaped body attached to 
the leaves of .plants. Their feet are atrophied. Their 
mouths are embedded into the tissue of the plant, the 
juices of which they suck. The whole mental activity of 
this motionless female parasite consists in the enjoyment it 
derives from sucking these juices and from sexual inter- 
course with the unattached male. The same is true of the 
maggot-like female of the Twisted-wings (Strepsiptera), 
which spends its whole life, wingless and footless, as a 
motionless parasite in the body of the wasp. There can be 
no suspicion of any higher mental activity there. If these 
brutish parasites are compared with the mentally active 
and sensible ants, it will certainly be admitted, that the 
psychical diflferences between the two are much greater 
than those between the highest and lowest Mammals, 
between Beaked Animals (Ornithostoma), Pouched Animals 
{Marsupialia), and Armadillos on the one hand, and Dogs, 
Apes, and Men on the other. And yet aU those insects 
belong, without question, to the single class of Arthropoda, 
just as all these Mammals undoubtedly belong to the single 
class of Vertebrates ; and just as every logical adherent of 
the doctrine of evolution must assume a common parent- 
form for aU those Insects, so also he must necessarily assert 
a common descent for all these Mammala. 



450 THE EVOLUTION OF MAN. 

Turning now from observing the comparative mental 
capacity of the various animals to the question as to the 
organs of these functions, we receive the answer, that in all 
higher animals they are invariably connected with certain 
groups of cells, those cells which compose the central 
nervous system. All naturalists, without exception, agree 
that the central nervous system is the organ of the mental 
life of animals, and this assertion is at any time capable 
of experimental proof If the central nervous system is 
wholly or partially destroyed, the " mind," or the psychical 
activity of the animal, is wholly or partially annihilated at 
the same time. We must, therefore, next inquire what is 
the character of the mental organ in man. The undeniable 
answer to this question has already been given. Man's 
mental organ is, in its whole structure and origin, the same 
as that of all other Vertebrates. It originates as a simple 
medullary tube from the outer skin of the embryo, from 
the skin-sensory layer, or the first of the secondary germ- 
layers. In the course of its gradual development it passes 
through the same stages of progression in the human 
embryo as in that of all other Vertebrates, and as these 
latter have undoubtedly a common origin, so must also the 
brain and spinal cord be of the same origin in all. 

Physiological obsei'vation and experiment teaches, more- 
over, that the relation of the " mind " to its organ, the brain 
and spinal marrow, is exactly the same in Man as in all 
other Mammals. The former can in no case act without 
the latter; the one is connected with the other, as is 
muscular movement with muscle. Therefore, the mind can 
develop only in connection with its organ. Adherents of 
Uie Theory of Descent, who concede the causal connection 



DEVELOPMENT OF THE HUMAN MIND. 45 1 

between Ontogeny and Phylogeny, are now compelled to 
recognize the following propositions : The mind, or " psyche," 
of man has developed together with, and as the function of 
the medullary tube, and just as even now the brain and 
spinal marrow develop in each human individual from the 
simple medullary tube, so the human " mind," or the mental 
capacity of the entire human race, has developed gradually, 
step by step, from the mind of lower Vertebrates. Just as 
even now in every individual of the human race the 
wonderful and complex structure of the brain develops 
step by step from exactly the same rudiment, from the 
same five simple brain-bladders, as in all other Skulled 
Animals (Craniota), so the human mind has gradually 
developed in the course of millions of years from the mind 
of lower Skulled Animals ; and as now the brain of every 
human embryo difierentiates according to the special type 
of the Ape-brain, so also the human psyche has historicallj 
difierentiated from the Ape-mind. 

This monistic idea will, of course, be indignantly re- 
jected by most people, who accept the contrary dualistic 
view, which denies the inseparable connection of the brain 
and the mind, and regards " body and mind " as entirely 
separate and distinct ; but how shall we reconcile this 
commonly accepted view with the facts taught by the 
history of evolution ? The dualistic view is, at least, as 
irreconcilably opposed to Ontogeny as to Phylogeny. If 
we agree with the majority of men, that the mind is a self- 
existent, independent being, which has originally nothing 
to do with the body, but only dwells in it for a time, and 
which gives expression to its emotions through the brain, 
as the piano-player through his instrument, then we must 



45a TKEi EVOLUTION OF MAN. 

suppose a period in the human germ-history, at which the 
mind enters the body, enters the brain ; and we must also 
suppose a moment at death, at which it leaves the body ; 
and further, as every man inherits certain individual 
mental qualities from each parent, we must suppose that 
portions of the mind of each were transferred to the germ 
at the time of its procreation. A little piece of the father's 
mind accompanied the sperm-cell, a little piece of the 
mother's mind remained with the egg-cell. This dualistic 
view entirely fails to explain the phenomena of evolution. 
We all know that the new-bom child has no consciousness, 
no knowledge of itself and of the objective world. Who- 
ever has children of his own, and follows their mental 
development candidly, cannot possibly deny that processes 
of biological evolution are at work there. Just as all other 
functions of the body develop in connection with their 
organs, so does the mind develop in connection with the 
brain. And this gradual development of the child's mind 
is such a wonderful and beautiful phenomenon, that every 
mother and every father with eyes to see takes unwearied 
delight in observing it. The text-books of Psychology 
alone are ignorant of any such development, and we are 
almost forced to the conclusion that their authors them- 
Belves never had any children. The human mind, as it is 
represented in the great majority of psychological works, 
is only the one-sided mind of a learned philosopher, who, 
indeed, knows many books, but nothing of the process of 
evolution, and does not suspect that even his own mind has 
developed. 

These same dualistic philosophers must, of course, it 
they are consistent, also assume that there was a moment 



K£Aii02(. 453 

in the Phylogeny of the human mind at which this mind 
first entered the vertebrate body of man. Accordingly, at 
the time when the human body developed from the body 
of the Anthropoid Ape (thus, probably, in the latter part of 
the Tertiary Period), a specific human mind-element — or, as it 
is usually expressed, a "divine spark " — must have suddenly 
entered or been breathed into the brain of the Anthropoid 
Ape, and there have associated itself with the already 
existing Ape-mind. I need not point out the theoretic 
difficulties involved in this conception. I will only remark 
that even this " divine spark," by which the mind of Man 
is said to be distinguished from that of all other animals, 
must itself be a thing capable of evolution, and has actually 
developed progressively in the course of human history. 
This "divine spark "is usually understood to be "reason,' 
and is ascribed to man as a mental function distinguishing 
him from all "irrational animals." Comparative Psycho- 
logy, however, teaches that this frontier-post between man 
and beast is altogether untenable.^^^ We must either take 
the idea of reason in its broader sense, in which case it 
belongs to the higher Mammals (the Ape, Dog, Elephant, 
Horse), as much as to the majority of men ; or we must 
conceive it in its narrower sense, and then it is lacking in 
the majority of men, as well as in most animals. On the 
whole, that which Goethe's Mephistopheles said of his time, 
11 true of Man's reason to-day : 

*• He might have kept himself more right 
Hadst Thon ne'er shewn to him a glimpse of heaven'i ligki. 
He calls it Reason, but Thou seest 
Its use but makes him beastlier than the beast." 

It therefore, we must abandon this generally preferred. 



454 THE EVOLUTION OP HO. 

and, in many respects, very pleasant dualistic theory of the 
mind, as being wholly untenable, because irreconcilable 
with genetic facts, then the opposite monistic view alone 
remains to us, according to which the human mind, like 
that of any other animal, is a function of the central nervous 
system, with which it has developed in inseparable con- 
nection. Ontogenetically, we see this in every child ; 
phylogenetically, we must assert it in accordance with the 
fundamental law of Biogeny. In every human embryo 
the medullary tube develops from the skin-sensory layer, 
and from the anterior part of that tube the five brain- 
bladders of Skulled Animals (Graniota), and from these 
the mammalian brain (at first with the characteristics of 
the lower, then with those of the higher Mammals). 
Just as this entire ontogenetic process is but a short repro 
duction, occasioned by Heredity, of the same process in the 
Phylogeny of Vertebrates, so also the wonderful mental 
activity of the human race has gradually developed, step 
by step, in the course of many thousands of years, from tho 
less perfect mental activity of the lower Vertebrates. And 
the evolution of the mind in each child is only a brief 
reproduction of that long phylogenetic process. 

The extraordinary and important bearing of Anthro- 
pogeny on Philosophy, in the light of the fundamental prin- 
ciple of Biogeny, now becomes apparent. The speculative 
philosophers who will take possession of the facts of On- 
togeny and explain them phylogenetically (according to that 
law), will introduce a greater advance in the history of 
Philosophy than has been made by the greatest thinkers of 
all previous centuries. Undoubtedly every clear and logical 
thinker must draw from the facts of Comparative Anatomy 



PHILOSOPHICAL ASPECT OF EVOLUTION. 455 

and Ontogeny which have been brought forward, a mass 
of suggestive thoughts and reflections which cannot fail 
of their effect on the further development of the philo- 
sophical study of the universe. Neither can it be doubted 
that these facts, if properly weighed, and judged without pre- 
judice, will lead to the decisive victory of that philosophical 
tendency, which we distinguish, briefly, as monistic or 
mechanical, in distinction from the dualistic or teleological, 
on which most philosophical systems of ancient, mediaeval, 
and modem times are based. This mechanical, or monistic 
philosophy, asserts that everywhere the phenomena of 
human life, as well as those of external nature, are undei 
the control of fixed and unalterable laws, that there is 
everywhere a necessary causal connection between pheno- 
mena, and that, accordingly, the whole knowable universe 
forms one undivided whole, a " raonon" It further asserts, 
that all phenomena are produced by mechanical causes 
(causce ejfficientes), not by pre-arranged, purposive causes 
{causae finales). Hence there is no such thing as "free- 
will " in the usual sense. On the contrary, in the light of 
this monistic conception of nature, even those phenomena 
which we have been accustomed to regard as most free and 
independent, the expressions of the human will, appear as 
subject to fixed laws as any other natural phenomenon 
Indeed, each unprejudiced and searching test appKed to the 
action of our " free-will " shows that the latter is never 
reaUy free, but is always determined by previous causal 
conditions, which are eventually referable either to Heredity 
or to Adaptation. Accordingly, we cannot assent to the 
popular distinction between nature and spirit. Spirit 
exists everywhere in nature, and we know of no spirit out- 



456 THE EVOLUTION OF MJlN. 

side of nature. Hence, also, the usual distinction between 
natural science and mental science is entirely untenable. 
Every real science is at the same time both a natural and a 
mental science. Man is not above nature, but in nature. 

The opponents of the doctrine of evolution are very fond 
of branding the monistic philosophy grounded upon it as 
" materialism," by confusing philosophical materialism with 
the wholly different and censurable moral materialism. 
Strictly, however, our " monism " might, as accurately or as 
inaccurately, be called spiritualism as materialism. The 
real materialistic philosophy asserts, that the vital pheno- 
mena of motion, like all other phenomena of motion, are 
effects or products of matter. The other, opposite extreme, 
spiritualistic philosophy, asserts, on the contrary, that 
matter is the product of motive force, and that all material 
forms are produced by free forces entirely independent of 
the matter itself. Thus, according to the materialistic 
conception of the universe, matter, or substance, precedes 
motion, or active force. According to the spiritualistic con- 
ception of the universe, on the contrary, active force or 
motion precedes matter. Both views are dualistic, and we 
hold them both to be equally false. A contrast to both 
views is presented in the monistic philosophy, which can as 
little believe in force without matter, as in matter without 
force. It is only necessary to reflect on this for a time, 
from a strictly scientific standpoint, to find that on close, 
examination it is impossible clearly to represent the one 
without the other. As Goethe says, "Matter can never 
exist and act without spirit; neither can spirit without 
matter." " 

The " spirit " and " mind " of man are but forces which 



BKASON A FUNCTION OF MIND. 45/ 

are inseparably connected with the material substance of 
our bodies. Just as the motive force of our flesh is involved 
in the muscular form-elepaent, so is the thinking force of 
our spirit involved in the form-element of the brain. Our 
spiritual forces are as much functions of this part of the 
body, as every force is a function of a material body. W© 
know of no matter which does not possess force, and, con- 
versely, of no forces that are not connected with matter. 
When the forces manifest themselves in the phenomena of 
motion, they are called active forces ; if, on the other hand, 
the forces are in a state of rest, or of equilibrium, they are 
called latent forces.^^^ This is as true of inorganic natural 
substances as of organic. The magnet attracting iron- 
filings, powder exploding, steam driving the locomotive, are 
active inorganic substances ; they work by active force just 
as does the sensitive mimosa, when it folds its leaves at a 
touch, — as does the Amphioxus, when it buries itself in the 
sand, — as does man, when he thinks. Only in these latter 
cases the combination of the different forces, appearing as 
phenomena of motion, are much more complex and much 
less easily recognized than in the former cases. 

Anthropogeny has led us to the conclusion that even in 
the entire history of the evolution of man, in the history of 
the germ, as well as in that of the tribe, no other active 
forces have been at work, than in the rest of organic and 
inorsanic nature; All the forces at work there can be 
reduced at last to growth — to that fundamental function of 
evolution by which the forms of inorganic, as well as of 
organic bodies, originate. Growth, again, itself rests on the 
attraction and repulsion of like and unlike particles.^^^ It 
boa given rise to Man and to Ape, to Palm and Alga, to 



453 THE EVOLUTION OF MAN. 

crystal and water. Hence the evolution of man has taken 
place according to the same " eternal, immutable laws," 
as has the evolution of any other natural body. 

It is true that the prejudices that stand in the way of 
the general recognition of this " Natural Anthropogeny " 
are even yet intensely powerful ; otherwise the ancient 
strife between the various philosophical systems would 
already have been decided in favour of "Monism.*' But 
it can be foreseen with certainty that a more general 
acquaintance with genetic facts, will gradually destroy 
those prejudices and bring about the victory of the 
natural idea of "Man's Place in Nature." The fear is 
often expressed in opposition to this view that it will cause 
a retrogression in the intellectual and moral development 
of man ; but, on the contrary, I cannot withhold my convic- 
tion, that the very reverse will be true, that by it the pro- 
gressive development of the human spirit will be advanced 
in an unusual degree. At all events, I hope and trust tliat 
I have, in these chapters, afforded convincing proof that 
the only way to attain a true scientific knowledge of the 
human organism, is by employing the method which we 
must acknowledge to be alone correct and successful in the 
study of organic nature, — by following the course of the 
ffistory of Evolution.200 



NOTES. 



UEMARKS AND REFERENCES TO LITBRATURB. 



1 (vol. i. p. 2). Anthropogeny (Greek) = History of the Bvoln- 
fcion of Man; from Anthropos (av^pwTros) = man, and genea (yevea) 
= Evolution history. There is no especial Greek word for " the 
history of evolution ; " in its place is used either yeved ( = de- 
scent), or yoveia (= generation). If goneia is preferred to 
genea, the word must be written Anthropogeny. The word 
" Anthropogony,'^ used first by Josephus, means, however, only 
" the generation of man." Genesis (yei/eo-ts) means " origination, 
or evolution ; " therefore Anthrojpogenesis = " the evolution of 



man." 



2 (i. 3). Embryo (Greek) = germ {tfjiPpvov). Really to cvtos 
r^s ya(TTpo'i ppvov (Eust.), i.e. the unborn germ in the mother's 
body (Latin foetus, or, better, fetus). In accordance with this 
original sense, the term embryo should only be applied to those 
young organisms which are still enclosed in the egg- coverings. 
(Cf. " Generelle Morphologie," vol. ii. p. 20.) Inaccurately, how- 
ever, various free-moving young forms of low animals (larvae) 
are often spoken of as embryos. Embryonic life ends at birth. 

3 (i. 5). Embryology (Greek) = Germ-science, from embryon 
{tfxppvov) = germ, and logos (Aoyos) = science. Even now the 
whole history of the evolution of the individual is erroneously 
called "embryology." For corresponding with the term 
"embryo" (see note 2), by "embryology," or " embryogony," 
should only be understood " the history of the evolution of ihe 



460 NOTES. 

individual within the egg-coverings." As soon as the organism 

has left there, it is no longer a real " embryo." The later changes 
of this form the subject of the science of Metamorphoses, or 
MetainoTrphology. 

4 (i. 5). Ontogeny (Greek) =" germ-history," or "the 
history of the evolution of the individual;" from oKra = indi- 
viduals, and genea (ycvea) = history of evolution. (Cf. note 1.) 
Ontogeny, as the "history of the evolution of the individual," 
embraces both Embryology and Metamo^phology (note 3). — 
"Grenerelle Morphologic," vol. ii. p. 30. 

5 (i. 5). Phylogeny (Greek) = tribal history, or " the pa- 
IsBontological history of evolution ; " from phylon (^uAoi/) = tribe, 
fcnd genea (yci/ea) = history of evolution. The phylon includes 
all organisms connected by blood, which are descended from a 
common typical parent-form. Phylogeny includes Pala3ontology 
and Genealogy. — " Generelle Morphologic," vol. ii. p. 305. 

6 (i. 6). Biogeny (Greek) = the history of the evolution of 
organisms or of living natural bodies in the widest sense 
(Genea tu biu.) )Stos = life. 

7 (i. 6). The fundamental law of Biogeny. Cf. my "General 
History of the Evolution of Organisms" (" Generelle Morphologic," 
1866, vol. ii.), p. 300 (Essays on the causal connection of biogenetic 
and phyletic evolution) ; also the " Monograph of Chalk 
Sponges " (" Monographic der Kalkschwamme," 1872, vol. i. 471); 
also my " Natural History of Creation." 

8 (i 10). Palingenesis (Greek) = original evolution, from 
palingenesia (TroAtvyevco-ia) = new-birth, renewal of the former 
course of evolution. Therefore, Palingeny = inherited history 
(from TToXtv = reproduced, and y€vca= history of evolution). 

9 (i. 10). Kenogenesis (Greek) = modified evolution, from 
kenos (/c€i/os) = strange, meaningless; and genea (yevea) = history 
of evolution. The modifications introduced into Palingenesis 
by Kenogenesis are vitiations, strange, meaningless additions to 
the original, true course of evolution. Kenogeny — vitiated 
history. 

10 (i. 12). Latin dafinitioB ol the fundamental law 9k 



NOTES. 461 

Biogen J : " Ontogenesis snmmarinm vel recapitnlatio est phy- 
logeneseoa, tanto integrins, quanto hereditate palingenesis con- 
serratnr, tanto minns integrum, quanto adaptatione kenogenesis 
introdncitnr." Cf . my " Aims and Methods of Recent History 
of Evolution " (" Ziele und Wage der Heutigen Entwickelunga- 
geschichte," p. 11. Jena, 1876). 

11 (i. 17). Mechanical and purposive causes. Meclianical 
natural philosophy assumes that throughout nature, in organic 
as well as in inorganic processes, only non-purposive, mechanical, 
necessarily-working causes exist (causce ejfficienteSy mecho/nism, 
causality). On the other hand, vitalistic natural philosophy 
asserts that the latter are at work only in inorganic processes, 
which in certain other, purposive, special causes are at work, 
conscious or purposive causes, working for a definite end (causce 
UnaleSy Vitalism^ Teleology). (Cf. " Generelle Morphologic," 
vol. i. p. 94.) 

12 (i. 17). Monism and Dualism. Unitary philosophy, or 
Monism, is neither extremely materialistic nor extremely spirit- 
ualistic, but resembles rather a union and combination of these 
opposed principles, in that it conceives all nature as one whole 
and nowhere recognizes any but mechanical causes. Binarv 
philosophy, on the other hand, or Dualism, regards nature and 
spirit, matter and force, inorganic and organic nature as distinct 
and independent existences. (Cf. vol. ii. p. 456.) 

18 (i. 20). Morphology and Physiplogy. Morphology (as 
the science of forms) and Physiology (as the science of the 
functions of organisms) are indeed connected, but co-ordinate 
sciences, independent of each other. The two together constitute 
Biology, or the " science of organisms." Each has its peculiar 
methods and aids. (Cf . ** Generelle Morphologic," toL i, pp. 
17-21.) 

14 (i. 24). Morphogeny and Physiogeny. Biogeny, or the 
'* history of the evolution of organisms," up to the present time 
has been almost exclusively Morphogeny. Just as this first 
opens the way to a true knowledge of organic forms, so will 
Physiogeny afterwarda make a tme recognition of functions 



462 NOTES. 

possible, by discovering tbeir historic evolntion. Its future 
promises to be most fruitful. Cf . " Aims and Methods of the 
Recent History of Evolution" (" Ziele und Wege der Heutigen 
Entwickelungsgeschichte," pp. 92-98. Jena, 1876). 

15 (i. 27). Aristotle. Five books on the generation and 
evolution of animals (Trcpt ^cowv yei/ccreos). 

16 (i. 28). Parthenogenesis. On " virginal generation," 
or the ''immaculate conception" of Invertebrates, especially of 
Articulated Animals {Crustacea, Insecta, etc.), see Siebold. 
"Remarks on Parthenogenesis among Arthropoda " (" Beitrage 
zur Parthenogenesis der Arthropoden." Leipzig, 1871). Georg 
Seidlitz, " Parthenogenesis and its Relation to other Forms of 
Generation in the Animal Kingdom " (" Die Parthenogenesis und 
ihr Verbal tniss zu den iibrigen Zeugungs-Arten im Thierreich." 
Leipzig, 1872). 

17 (i. 34). The Preformation-theory. This theory is, in 
Germany, usually called " E volutions- theorie,"iu distinction from 
the " Epigenesis-theorie." As, however, in England, France, and 
Italy, the latter is, on the contrary, usually called the theory of 
evolution, evolution and epigenesis being used as synonymous 
terms, it appears better to call the former " the theory of pre- 
formation." Recently Kolliker has called his " theory of hetero- 
genous generation " " Evolutionism " (note 47). Cf. preface, 

p. XXX. 

18 (L 37). Alfred KirchhofE, "Caspar Friedrich Wolff, his 
Life and Teaching in the Science of Organic Evolution." — 
" Jenaische Zeitschrift fiir Naturwissenschaft," 1868, vol. iv 
p. 193. 

19 (i. 43). Part of the writings left by Wolff have not yet 
been published. His most important works are the dissertation 
for the degree of doctor, Theoria generationis (1759), and hii- 
model treatise " de formatione intestinorum " (on the formation 
of the intestinal canal). — "Nov. Comment. Acad. Sc. PetropoL," 
xii. 1768; xiii. 1769. Translated into German by Meckel. 
Halle, 1812. 

20 (i. 51). Christian Pander, ^^Sistoria metamorphoseos, qnam 



NOTES. 463 

ovmn incubattun prioribns qninque diebns snbit." Vicebergi, 
1817. (Dissertatio inauguralis.) " Contribntions toward the 
history of the evolntion of the chick within the egg.^* (" Beitrage 
znr Entwickelungsgeschichte des Huhnchens im Eie." Wurz- 
burg, 1817.) 

21 (i. 52). Karl Ernst Baer, "On the Evolution of Animals. 
Observations and Reflections " (" Ueber Entwickelungsgeschichte 
der Thiere. Beobachtung und Reflexion." 2 vols. Konigsberg, 
1827-1837). In addition to this chief work, cf. " Story of the 
Life and Writings of Dr. Karl Ernst Baer, told by himself " 
(" Nachrichten iiber Leben und Schriften des Dr. Karl Ernst 
Baer, mitgetheilt von ihm selbst." Petersburg, 1865). 

22 (i. 60). Albert Kolliker. His "History of the Evolution of 
Man and the Higher Animals " (" Entwickelungsgeschichte des 
Menschen und der hoheren Thiere *') . The 2nd (corrected) edition, 
1876, contains (pp. 28-40) a catalogue of ontogenetic literature. 
On the newer contributions to this, cf. the " Jahresberichte 
iiber die Leistungen und Fortschritte der Medicin " (Berlin), by 
Virchow and Hirsch (the " History of Evolution,** by Waldeyer) ; 
also the " Jahresberichte iiber die Fortschritte der Anatomie und 
Physiologic,'* by Hofmann and Schwalbe (Leipzig) ; the "History 
of Evolution," by R. Hertwig and Nitsche. Most of Kowalev- 
sky's researches are contained in the " Memoires de 1* Academic 
imperiale de St. Petersburg " (from the year 1866). Others are 
published in Max Schultze's "Archiv fur mikroskopische 
Anatomie," and in other periodicals. 

23 (i. 60). Theodor Schwann, " Microscopic Researches into 
the Identity in Structure and Growth of Plants and Animalg " 
(" Mikroskopische Untersuchungen iiber die Uebereinstimmung 
in der Structur und Wachsthum der Thiere und Pflanzen." 
Berlin, 1839). 

24 (i. 69). Ernst Haeckel, the Gastreea Theory, phylogenetic 
classification of the animal kingdom and homology of the germ- 
layers. — " Jenaische Zeitschrift fiir Naturwissenschaft," voL yiii. 
1874, pp. 1-56. 

25 (i. 75). Ernst Haeckel, "The History of Creation." 
London, 1876. 



464 NOTES. 

26 (i. 81). Fritz Schultzo, " Kant and Darwin." A con- 
tribntion to the history of tho science of evolution. Jena, 1875. 

27 (i. 81). Immanuel Kant, "Critique of Teleological Rea- 
son" ("Kritik der teleologischen Urtheilskraft "). 1790. § 74 
and § 79. Cf. also my " History of Creation," vol. i. p. 103. 

28 (i. 83). Jean Lamarck, " Philosophie Zoologiqne, ou 
Exposition des Considerations relatives a I'histoire natureUe des 
animaux," etc. 2 Tomes. Paris, 1809. Nouvelle edition, revue 
et precedee d*une introduction biographique par Charles Martins. 
Paris, 1873. 

29* (i. 88). Wolfgang Goethe on Morphology (zur Morpho- 
logie). The formation and re-formation of organic bodies. On 
Goethe's morphological studies, cf. Oscar Schmidt (" Goethe's 
Yerhaltniss zu den organischen Naturwissenschaften." Jena, 
1853). Rudolph Yirchow, "Goethe as a Naturalist" (Berlin, 
1861). Helmholtz, " On Goethe's Natural Scientific Works " 
(Brunswick, 1865). 

30 (i. 96). Charles Darwin. His chief work is " On the 
Origin of Species by means of Natural Selection " (1859). 

31 (i. 99). Darwin and Wallace. The general outlines of 
the theory of selection were discovered independently by Darwin 
and Wallace. It does not, however, follow that the services 
or the latter in furthering the science of evolution are at ail 
comparable with those of the former. As many opponents of 
Darwin, especially the English Jesuit Mivart, have recently 
endeavoured to exalt Wallace at the expense of Darwin, and to 
depreciate the latter, I take this opportunity of expressly assert- 
ing that Darwin's services are very far the greater. 

32 (i. 101). Thomas Huxley. In addition to the works 
mentioned in the text, the following popular works are especially 
to be recommended : " On Our Knowledge of the Causes of 
Phenomena in Organic Nature," and the "Elementary Phy- 
siology " (1871). 

33 (i. 101). Gustav Jaeger, " Zoological Letters " ("Zoologische 
Briefe." Vienna, 1876), and the " Text-book of General Zoology" 
(" Lehrbuch der Allgemeinen Zoologie." Stuttgart, 1876). 



NOTES. 465 

34 (1. 101). Friedricli Rolle, "Man, his Descent and Morality 
represented in the light of the Darwinian Theory, and on the 
basis of Recent Greological Discoveries " (" Der Mensch, seine 
Abstammung und Gesittung im Lichte der Darwin'schen Lehre," 
etc.). Frankfort, 1866. 

35 (i. 102). Ernst Haeckel, " Generelle Morphologie der 
Organismen." General outlines of the science of organic forms, 
mechanically shown in accordance with the theory of descent as 
reformed by Charles Darwin. Vol. i., " General Anatomy ; " 
vol. ii., " General History of Evolution." Berlin, 1866. 

36 (i. 103). Charles Darwin, "The Descent of Man, and 
Selection in Relation to Sex." 2 vols. London, 1871. 

37 (i. 108). Karl Gegenbaur, "Outlines of Comparative 
Anatomy" ("Grundziige der vergleichenden Anatomie." Leipzig. 
2nd ed., 1870). "Elements of Comparative Anatomy " (" Grundriss 
der vergleichenden Anatomie." 3rd (improved) edition, 1874). 

38 (i. 114). Migration-theory. Moritz Wagner, " The Dar- 
winian Theory and the Law of Migration of Organisms " (" Die 
Darwin'sche Theorie und das Migrations-gesetz der Organ- 
ismen." Leipzig, 1868). August Weismann, "On the Influence 
oP Isolation in the Formation of Species " (" Ueber den Einfluss 
der Isolirang auf die Artenbidung." Leipzig, 1871). 

39 (i. 116). Carus Sterne, "Evolution and Dissolution" (" Wer- 
den und Vergehen"). A popular history of the evolution of 
nature as a whole. Berlin, 1876. Agassiz a "founder" of 
natural science. " Gegenwart." Berlin, 1876. 

40 (i. 117). Ernst Haeckel, "The Chalk-sponges" ("Die 
Kalkschwamme ; Calcispongien oder Grantien." Berlin, 1872). 
A monograph and an attempted solution of the problem of the 
origin of species. Vol. i., " Biology of Chalk-sponges ; " vol. ii., 
" Classification of Chalk-sponges ; " vol. iii., " Atlas of Chalk- 
sponges " (with 60 plates). 

41 (i. 124). On the Individuality of Cells and recent reforms 
in the cell-theory, cf. my " Individuahtatslehre," or " Tectologie " 
("Generelle Morphologie," vol. i. pp. 239-274). Rudolf 
Virchow, "(/ellular Pathologic." 4th edition. Berlin, 1871. 



4-66 MOTEa 

42 (i. 130). "The Plastid-tlieory and the Cell-theorf.**— 
" Jenaische Zeits'chrift fiir Naturwissenschaft," 1870, vol. v. p. 
492. 

43 (i. 138). Gegenbaur, " On the Stmcture and Evolution of 
Vertebrate Eggs with Partial Yelk-cleavage." — " Archiv f . Anat. 
u. Phys." 1861, p. 491. 

44 (i. 163). Ernst Haeckel, "On Division of Labour in Nature 
and Human Life," in the collection of Lectures by Virchow- 
Holtzendorf, 1869. Sect. 78 2nd edition. 

45 (i. 160). Monogony {Generatio neutralis). On the various 
forms of asexual reproduction (Schizogony, Sporogony, etc.), cf. 
" Generelle Morphologic," vol. ii. pp. 36-58. 

46 (i. 160). Amphigony (^Generatio sexualis). On the various 
forms of sexual reproduction (Hermaphroditism, Gonochorism, 
etc.), see " Generelle Morphologic," vol. ii. pp. 58-69. 

47 (i. 168). Fitful evolution and gradual evolution. The 
theory of fitful evolution has recently been developed especially 
by Kolliker, who, under the title of heterogeneous generation, 
opposes it to gradual evolution as maintained by us (" Zeitschr. 
f. Wissens. Zool.," vol. xiv. 1864, p. 181, and " Alcyonaria, " 1872, 
pp. 384-415). This theory is distinguished by assuming entirely 
unknown causes for the "fitful evolution of species," a so-called 
"great law of evolution" (an empty word indeed!). On the 
contrary, we see, with Darwin, in the facts of Heredity and 
Adaptation sufficient known (partly inner, partly external) 
physiological causes, which explain the gradual evolution of 
species under the influence of the struggle for existence. 

48 (i. 170). Immaculate Conception never occurs in the 
vertebrate tribe. On the other hand, parthenogenesis frequently 
occurs among Articulated Animals (Artliropoda) (note 16). 

49 (i. 171). Fertilization of Flowers by insects. Charles 
Darwin on " The various contrivances by which British and 
Foreign Orchids are fertilized by Insects." Hermann Miiller on 
" The Fertilization of Flowers by Insects, and the correlative 
adaptations of both " (" Die B«fruchtung der Blumen durch 
Insecten nnd die gegonseitigen Ajipassungen Beider "). A con* 



NOTES. 467 

fcribntion to our knowledge of causal connection in organic 
nature. Leipzig, 1873. 

60 (i. 178). The Process of Fertilization has been very 
varionsly viewed, and was formerly often regarded as an 
entirely mysterions process, or even as a snpernatural miracle. 
It now appears no more " wonderful or supernatural " than the 
process of digestion, of muscular movement, or of any other 
physiological function. For the earlier views, cf. Leuckart, 
Article " Zeugung " (generation) in R. "Wagner's " Dictionary 
of Physiology," 1850. 

61 (i. 179). Monerula. The simple, very transient, kernel- 
less condition, which we briefly call the "monerula," and, in 
accordance with the fundamental law of Biogeny, regard as a 
palingenetic reproduction of the phylogenetic Moneron parent- 
form, appears to vary to some extent in different organisms, 
especially in the matter of duration. In those cases in which 
it no longer occurs, and in which the kernel of the fertilized 
egg persists wholly or partially, we may regard this phenomenon 
as a later, kenogenetic curtailment of Ontogeny. 

52 (i. 181). The Plasson of the monerula appears, mor- 
phologically, a homogeneous and structureless substance, like 
that of the Moneron. This is not contradicted by the fact that 
we ascribe a very complex molecular structure to the plastidules, 
OP " plasson-molecules," of the monerula ; this latter will 
natnrally be more complex in proportion as the organism which 
it ontogenetically constitutes is higher, and as the ancestral 
series of that organism is longer, in proportion as the preceding 
processes of Heredity and Adaptation are more numerous. 

63 (i. 182). The Fundamental Significance of the Parent-cell, 
or cytnla, as the foundation-stone of the young organism in the 
course of development, can only be rightly appreciated, if the 
part taken in its constitution by the two generating cells is 
rightly appreciated, the part taken by the male sperm-cell and 
by the female egg-cell. 

64 (i. 183). The One-celled Germ-organism, like the act of 
fertilization from which it results, has been very variously 



46S NOTES. 

▼lewed. Cf. on this stibiect, in addition to the fonr important 
works, here qnoted, by Anerbach, Biitschli, Hertwig, and Stras- 
bnrger, the most recent annals of the progress of the history of 
evolution (Waldeyer in Virchow-Hirsch's " Jahresberichten," 
Berlin ; Hertwig in Hofmann-Schwalbe's " Jahresberichten., * 
Leipzig). 

55 (i. 185). Protozoa and Metazoa. Cf. vol. i. p. 248; ii. 92. 
The Protozoa and Metazoa are genetically and anatomically so 
very distinct, that the former, as Protista, may even be excluded 
entirely from the animal kingdom, and may be regarded as a 
neutral intermediate kingdom between the plant and animal 
kingdoms. — "Generelle Morphologic," vol. i. pp. 191-230. Ac- 
cording to this view the Metazoa alone are really animals. 

56 (i. 186). The Unity of the Zoogenetic Conception, result- 
ing from the Gastraea-theory, has as yet not been destroyed by 
the numerous attacks directed against that theory : for none of 
these attacks have succeeded in substituting anything positive ; 
by pure negation no advance can be made in this dark ani 
difficult subject. 

57 (i. 187). The Egg-cleavage and Gastrulation of Man, as 
represented diagrammatically in Figs. 12-17 of Plate II., is most 
probably in no essential way different from that of the Rabbit, 
which has as yet been most closely examined in this point. 

58 (i. 188). Ernst Haeckel, " Arabian Corals " (" Arabische 
Korallen"). "A Journey to the Coral Banks of the Red Sea, and 
a Glimpse into the Life of Coral Animals. A popular lecture, 
with scientific explanations." With 5 coloured plates, and 20 
woodcuts. Berlin, 1876. 

59 (i. 189). The Number of the Segmentella, or cleavage- 
cells, increases, in the original, pure forms of palingenetic egg- 
cleavage, in regular geometric progression. But the point to 
which this proceeds varies in the various archiblastic animals, 
BO that the Morula, as the final result of the cleavage-process, 

' consists sometimes of 32, sometimes of 64, sometimes of 128 
cells, and so on. 

60 (L 189). The Mulberry-germ, or Morula. The seg- 



KOTSS. 469 

menteOa, or cleaTage- cells, which constitute the Morula at the 
close of palingenetic egg-cleavage, generally appear entirely 
similar, with morphological difference in size, form, or con- 
gtitntion. This does not, however, hinder the fact that these 
cells have separated, even during cleavage, into animal and 
vegetable cells, have differentiated physiologically, as is indicated 
in Figs. 2 and 3, Plate II., as probable. 

61 (i. 189). The Bladder-germ of Archiblastic Animals 
(hlastulaf or hlastosphcera)', which is now commonly known as 
the germ-vesicle, or, more accurately, as the " germ-membrane 
vesicle," must not be confused with the essentially different 
" germ-vesicle " of amphiblastic mammals, which is better called 
the *' intestinal-germ vesicle" (gastrocystia) . The gastrocystis 
and the blastula are still often united under the name of " germ- 
v^esicle, or vesicula hlastodermica." Cf. vol. i. p. 290. 

62 (i. 192). The Definition of the Gastrula was first 
established by me in 1872, in my "Monograph of Chalk-sponges " 
(vol. i. pp. 383, 345, 4i66). There I already gave due weight to 
the " extremely great significance of the gastrula in reference 
to the general Phylogeny of the animal kingdom" (p. 333). 
" The fact that these larval forms re-occur in the most different 
animals, cannot, I think, be sufficiently estimated, and bears 
plain witness to the former common descent of all from the 
Gastrsea " (p. 345). 

63 (i. 194). The Uniaxial Outline of the Gastrula is, on 
account of the two different poles of the axis, more accurately 
described as a diplopolic uniaxial form (a sternometric outline : 
conoid-form, or cone). Cf. my " Promorphology " (" Generelle 
Morphologic," vol. i. p. 426). 

64 (i. 194). Primitive Intestine and Primitive Mouth. My 
distinction of the primitive intestine and primitive moutli 
(protogaster and protostoma) from the later, permanent intestine 
and mouth (metagaster and metastoma) has been variously 
attacked ; it is, however, as much justified as the distinction of 
the primitive kidney from the permanent kidney, of the primitive 
vertebrae from the permanent vertebrae. The primitive intestiiif 



470 Nona 

forms but a part of the permanent intestine, and the primitiTe 
mouth (at least in the higher animals) does not become the 
permanent month. 

65 (i. 196). Primitive germ-layers (hlastopkyUa) . As the 
two primary germ-layers (^entoderma and exodermd) originally 
form the sole histogenetic rudiment of the whole body, and as 
the mesodemia, the nutritive yelk, and all other accessory parts 
of the germ have developed only secondarily from the former, 
1 consider it very important to distinguish between the primary 
and secondary germ-layers. The latter, to distinguish them 
from the former, might be called "after germ-layers" (Jblcu- 
telasmd). 

66 (i. 201). Unequal Cleavage and Hood-gastrula (Seg- 
mentatio inoBqualis et Amphigastruld) . Next to Amphibia the 
most accessible examples for observation of unequal cleavage 
and the Amphigastrula are afforded by the indigenous Soft- 
bodied Animals (Mollusca) and Worms (Snails and Mussels, 
Earth Worms and Leeches). 

67 (i. 202). The Colour of Amphibian- eggs is occasioned by 
the accumulation of dark colouring- matter at the auimal pole of 
the egg. In consequence of this the animal-cells of the exoderm 
appear darker than the vegetative cells of the entoderm. In 
most animals the reverse is the case; the protoplasm of the 
entoderm cells being usually darker and more coarsely granulated 
(vol. i. p. 197). 

68 (i. 207). Hood-gastrula of Amphibia. Cf. Robert Remak, 
" On the Evolution of Batrachia " (" Ueber die Entwickelung der 
Batrachier," p. 126 ; Plate XII. Figs. 3-7). Strieker's " Manual 
of Tissues" ("Handbuch der Gewebelehre," vol. ii. p. 1195- 
1202; Figs. 399-402). Goette, "History of the Evolution of 
Bomhinator" (" Entwickelungsgeschichte der Unke," p. 145; 
Plate II. Figs. 32-35). 

69 (i. 214). Hood-gastrula of Mammals. Eduard van 
Beneden, " La maturation de Toeuf, la fecondation et les premieres 
phases du developpement embryonnaire des Mammiferes, d'aprea 
des recherches faites chez le lapin." Brussels, 1875 . No figures 



NOTE& 471 

are given with these *' Coranninication pr^liminaire ; " Van 
Bcneden's description is, however, so clear, so thoroagh and care- 
ful, that thev afford an entirely satisfactory insight into unequal 
egg-cleavage and the formation of the Hood-gastrula in Mammals. 
All other observers, who have studied the germination of Mam- 
malian eggs (among the most recent Kolliker, Rauber, and 
Hewsou may be especially mentioned), have overlooked or 
failed to recognize the important features discovered by Van 
Beneden. 

70 (i. 218). The Disc-gastrula (Disco-gastrvla) of Osseous 
Fishes (Teleostei). Van Bambeke, " Recherches sur I'embry- 
ologie des poissons osseux." Brussels, 1875. The transparent 
Fish-eggs, in which I observed discoid cleavage (Segmentatio 
discoidalis) and the formation of the Disc-gastrula by invagination, 
are accurately described in my article on " The Gastrula and 
Egg-cleavage of Animals " (" Jen. Zeitschrift fiir Naturwis- 
senschaft," 1875, vol. ix. p. 432-444; Plates IV., V.). On the 
Disc-gastrula of Selachiiy cf. Balfour, " The Development of 
Elasmo branch Fishes." — " Joum. of Anat. and Physiol.," vol. x. 
p. 517; Plates XX., XXIII. 

71 (i. 221). Yelk-cells of Birds. The cell-like constituent 
parts, which occur in great number and variety in the nutritive 
yelk of Birds and Reptiles, as in most Fishes, are nothing less 
than true cells, as His and others have asserted. This does not 
mean that in this matter a distinct limit everywhere exists 
between the nutritive and the formative yelks, as in our oceanic 
Fish-eggs (Figs. 42, 43, note 70). On the contrary, originally 
(phylogenetically) the nutritive yelk originated from part of the 
entoderm. 

72 (i, 223) Egg-cells of Birds. Notwithstanding the large 
nntritive yelk; the " after-egg " (metovum) of Birds and Reptiles 
10, in form- value, a single cell. The very small, active protoplasm 
of the " tread " does, however, indeed fall far short, in volume, 
of the huge mass of the yellow yelk-ball. The bird's eggs are 
absolutely the largest cells of the animal body. Cf. note 43, and 
Eduard van Beneden, " Recherches sur la composition et kb 



4/2 NOTEa. 

4 

signification de Tceuf." Brussels, 1870. Hubert Lndwig, "On 
Bgg-stnictnre in tbe Animal Kingdom " (" Ueber die Eibildung 
in Thierreicbe." Wiirzburg, 1874). 

73 (i. 226). Discoidal cleavage {Segmentatio discoidalis) ol 
Bird's eggs. Cf . Kolliker, " History of tbe Evolution of Man 
and tbe Higber Animals " (" Entwickelungsgescbicbte des Men- 
scben und der boberen Tbiere." 2nd edition, 1876, pp. 69-81 ; 
Figs. 16-22). 

74 (i. 227), Disc-gastrula (Disco-gastrula) of Birds. Cf. 
Rauber, "On tbe Place of tbe Cbick in tbe System of Evolu- 
tion " (" XJeber die Stellung des Hiibncbens im Entwickelungs- 
plan "). Leipzig, 1876. Foster and Balfour, " Tbe Elements of 
Embryology." London, 1874. 

75 (i. 231). Bladder-gastrula (Perigastrula) of Articulated 
Animals (^Arthrojpoda) . Cf. Bobretzky, "Russian Essay on tbe 
Gerra-bistory of Astacus and Pal?emon." Kiew, 1873. Also my 
own article on tbe gastrula and egg-cleavage. — " Jen. Zeitscbrift 
fiir Naturwissenscbaft." Vol. ix. pp. 444-452, Plate VI. 

^Q (i. 234). Tbe Four-layer Tbeory, wbicb was first clearly 
stated by Baer in 1837 (" Entwickelungsgescbicbte der Tbiere," 
vol. ii. pp. 46, 68), and wbicb we bave bere carried out logically, 
yet appears tbe only form of tbe germ-layer tbeory, wbicb, 
on comparative observation of all bigber animals, supplies a 
universal law of germination for all and at tbe same time meets 
tbe inconsistent reputations of many observers. 

77 (i. 239). Caspar Friedricb Wolff first indicated tbe Four- 
layer Tbeory (note 7Q^. Cf. tbe remarkable sentence, quoted at 
vol. i. p. 45, from bis pregnant work on tbe formation of the 
intestinal canal (note 19). 

78 (i. 24Q). Tbe Four Main Types of Gastmlation, wbicb 
are diagrammatical ly distinguisbed in Plates II. and III., and in 
Tables III. and IV. (vol. i. pp. 241, 242), are of course connected 
by intermediate forms. Tbese are transitions botb between tbe 
primordial and tbe unequal forms, and between tbe primordial and 
tbe superficial forms ; similarly, tbe unequal form of egg-cleavage 
is connected by twixt-f orms with tbe discoidal forms, which latter 



NOTES. 473 

is again, perhaps, connected in tlie same way with the enperficial 
form. 

79 (i. 241). The Gustmlation of the varions classes of 
animals has been far too little studied to enable ns thoroughly 
to summarize the distribution of the various forms withir the 
separate classes. Yet it is already evident that primordial egg- 
cleavage and the formation of the Archigastrula occur in the 
lowest classes of each tribe. 

80 (i. 243). The Rhythm of egg-cleavage is by no means as 
regular as might appear from the four first examples in the five 
tables. There are, on the contrary, many variations, and not 
infrequently an entirely irregular and very variable sequence of 
numbers occurs (especially in discoided cleavage). 

81 (i. 246). Definition of the Type. Cf. Gegenbanr, 
'' Elements of Comparative Anatomy," 1874, p. 59. 

82 (i. 246). Types and Phyla. AccordiDg to the prevailing 
" Type- theory," the types of the animal kingdom are parallel, 
and entirely independent ; according to my " GastraBa- theory," 
on the contrary, they are divergent tribes, connected at the 
roots ; according to the view of Glaus and other opponents, the 
latter is no essential distinction. 

83 (i. 248). The one-ceUed condition of Infusoria entirely 
forbids their morphological comparison with Metazoa. Cf. my 
article " On the Morphology of Infusoria " (" Jen. Zeitschrift 
fiir Naturwissenschaft " 1873, vol. vii. p. 516-568). 

84 (i. 257). The axes of the Vertebrate outline. Cf. my 
" Promorphology " (Stereometry of Organisms). — " Generelle 
Morphologic," vol. i. pp. 374-574. " Singly double-outlines " 
(Dipleura), p. 519. "Bilateral-symmetrical" forms in the fourth 
signification of the word. 

85 (i. 255). The Primitive Vertebrate Type, as it is repre- 
sented in Figs. 52-56, is a hypothetic diagram, which is principally 
founded on the outline of the Amphioxus, but^ in which the 
Comparative Anatomy of Ascidia and Appendicularia on the 
one side, of Cyclostomi and Selachii on the other, is regarded 
This diagram is by no means meant to be an " exact figure," but 



474 NOTES. 

a provisional stage in the hypothetic reconstruction of the 
unknown, long extinct parent-form of Vertebrates, an "Archi- 
tjpe." 

86 (i. 268). Only very uncertain assumptions can be made 
as to the sense-organs of the hypothetic parent-form, for these 
organs, more than any others, have been subject to adaptation!, 
and in Ascidia, as in the Amphioius, have probably been much 
atrophied. The earliest Vertebrates probably inherited a pair 
of eyes of very simple character and a pair of simple ear- vesicles 
from Worms. 

87 (i.. 267). The primitive kidneys were perhaps already 
metameric in the hypothetic parent-form of Vertebrates, so that 
in addition to the two longitudinal main canals (primitive 
kidney ducts) numerous transverse tubes (segmental canals) 
were connected with these main canals, a pair in each metameron 
of the middle part of the body. Perhaps these already opened 
through ciliated funnels into the body-cavity {cosloma)^ as is 
now the case in Annelids, and, according to Balfour, in the 
embryos of Selachii. Cf. Balfour, " Development of Elasmo- 
branch Fishes." — " Quarterly Journal of Microscopical Science." 
New Series, vol. liv. p. 323 ; " Journal of Anat. and Physiol." 
vol. X. 

88 (i. 273). The germination of Primitive Vertebrates. Cf. 
<vith Table VI., Table VII. (vol. i. p. 327), Table XI. (p. 467); 
also the diagrammatic figures in Plates IV. and V. with explana- 
tion (p. 321). 

89 (i. 276). The Germ-forms of the earliest Vertebrates, as 
they are represented in diagrammatic cross sections in Figs. 
62-69, can only, of course, be approximately guessed, and with 
the aid of Comparative Anatomy and Ontogeny. These 
hypothetic diagrams, therefore, by no means claim to be ac- 
cepted dogmatically, any more than do those in Figs. 52-56. 
(Cf. note 85.) 

90 (i. 280). Main incidents in Vertebrate germination. Of 
the main palingenetic incidents here enumerated, perhaps the 
sixth, ninth, and tenth originally occurred in a very dif« 



K0TB8. 475 

ferent form. The other seven now appear to be prettj well 

established. 

91 (i. 285). The flat germ-disc of Birds, which even now, in 
the opinion of most embryologists, represents the first starting- 
point in the formation of the embryo, and to which all other 
germ-forms have been referred, is, on the contrary, a late and 
much modified germ-form, which has arisen in consequence of 
the extension of the gastmla over the greatly enlarging nutritive 
yelk. 

92 (i. 289). Site of Fertilization. In Man, as in other 
Mammals, fertilization of the eggs probably usually takes place 
in the oviduct : here, the eggs which, at the rupture of the 
Graafian follicles, have emerged from the female ovary and 
passed into the outer opening of the oviduct, meet with the 
active sperm-cells of the male seed, which, during copulation, 
penetrated into the uterus, and from there passed into the inner 
opening of the. oviduct. Rarely, fertilization occurs even on the 
ovary, or not till within the uterus. (Cf. Chapter XXV.) 

93 (i. 293). The origin of the mesoderm in Mammals, as in 
other animals, is, at present, among the most obscure and con- 
tested points of Ontogeny. Remak, Balfour, and others derive 
it from the entoderm, Kolliker and others from the exoderm. 
Waldeyer, His, and others assert that both primary germ-layers 
take part in the formation of the mesoderm. The last assump- 
tion is, I believe, correct. (Cf. notes 76^ 77.^ 

94 (i. 297). The Germ-shield (Notaspis). The ordinary 
view, that the germ-shield (= Remak's " Doppelschild ") is the 
earliest rudiment of the actual embryo, results in many erroneous 
conclusions. It is, therefore, necessary to point out especially 
that the germ- shield represents the first well-defined central 
dorsal part of the embryo. 

95 (i. 317). Body Wall and Intestinal Wall. The morpho- 
logical distinction between' the body wall and the intestinal wall, 
certainly primordial, is probably referable to the simple primary 
germ-layers of the Grastrasa. If the skin-fibrous layer is derived 
from the exoderm, and the intestinal-fibrous layer from the 



4/6 NOTES. 

entoderm, this most simply explains the progressive development 
of this distinction, which may be traced through the series of 
Worms, and np to Vertebrates. 

96 (i. 320). Palingenetic and Kenogenetic germination. In 
the germ-history of Vertebrates no clear conception of the 
embryological process has yet been attained, because all authors 
have started from the higher Vertebrates (usually from the 
Chick) and have assumed that the form of evolution occurring 
in this case is original and typical. It is only since the germ- 
history of the Amphioxus has taught us the palingenetic, really 
original form of germination of Vertebrate organisms, that we 
have been enabled, by Comparative Ontogeny (and especially by 
the principles of the Gastraea theory), rightly to understand and 
to explain phylogenetically the kenogenetic forms of germination 
of higher Vertebrates. 

97 (i. 321). The Diagrams in Plates IV. and V. are as simple 
and abstract as possible, in order to render the desired general 
explanation as easy as possible. 

98 (i. 346). Primitive Vertebrae and Metamera. For the 
right conception of " primitive vertebral " structure it is espe- 
cially necessary to point out that the primitive vertebras are 
much more than their name indicates. They must, in fact, be 
conceived as individual, consecutive sections of the trunk, 
which have arisen one after the other, as true " metamera," or 
consecutive pieces (" Generelle Morphologic," vol. i. p. 312). 
Each primitive vertebra of a Vertebrate, like each trunk-segment 
or metameron of an Annelid or Arthropod, contains all the 
essential, morphological constituent parts, characteristic of the 
corresponding animal-tribe. 

99 (i, 349). Origin of the Primitive Vertebras. My concep- 
tion of these as individual, morphological " consecutive pieces," 
which, like the metamera of Cestods and Annelids, have arisen 
by terminal budding from a single unarticulated piece, has beeii 
much attacked. I therefore emphatically remark that I only 
understand tliis process in the widest sense. In both cases there 
Is certainly a reproduction of individual, like parts, which ]»t« 
originated (in time and space) consecutively. 



KOTsa 477 

100 (i. 361). The agreement among the germ-formfl of 
various Mammals is instructive especially because it shows us 
how, by diversity in the mode of evolution, the most diverse 
gtmctures can originate from one and the same form. As we 
actually see this in germ-forms, we may hypothetically assume 
the same to have occurred among tribe-forms. Moreover, 
this agreement is never absolute identity, but always only 
the very greatest similarity. Even the germs of the yarious 
individuals of a species are never actually identical. 

101 (i. 366). The law of the ontogenetic connection of 
systematically allied animal-forms has many apparent exceptions. 
These are, however, fully explained by the adaptation of the 
germ to kenogenetic conditions of existence. Where the palin- 
genetic form of evolution of the germ has been accurately 
transmitted by heredity, that law is always in force. Cf . Fritz 
Miiller, " Fiir Darwin " (note 111). 

102 (i. 367). Earliest human germs. Cf. Kolliker, "History 
of the Evolution of Man " ('* Entwickelungsgeschichte des Men- 
schen." 2nd edition, 1876, pp. 303-319). Also Ecker, "Icones 
physiologicse." Leipzig, 1859. Plates XXV.-XXXI. The 
earliest human germs which have yet been certainly recognized, 
were from twelve to fourteen days old, and were observed by 
Prof. Allen Thomson, of Glasgow. No opportunity has ever 
occurred for the observation of earlier germs. 

103 (i. 369). Human germs of three weeks (twenty to twenty- 
one days) exhibit in their whole structure that phylogenetic stage 
of evolution which, among extant V^ertebrates, is represented by 
the Cyclostomi (Lampreys and Hags, vol. ii. p. 103), and which 
must be referable to extinct Monorhine ancestors of similar 
etructure. 

104 (i. 370). Human germs of four weeks (twenty-five to 
thirty days), on the whole, exhibit in their whole structure that 
phylogenetic stage of evolution, which is exhibited in Sharks 
and Rays, among extant Vertebrates, and which is referable to 
similar extinct Primitive Fish ancestors (Proselachii). Of course 
thi« comparison is afEected by various kenogenetic modifications 



47^ vomi 

(both heterotopic and heterochronic), just as in the foniMK. 

(Cf. note 108.) 

105 (i. 374). The nose of Nosed-apes is much more difFererit 
from that of other Apes than from that of Man. Moreover, 
even the extreme variety and variability in the external form 
of the hnman nose shows how small is the morphological value 
of this organ, so important to the physiognomy. 

106 (i. 383). The bladder-like form of the hnman Allantois. 
Cf . W. Kranse, " On the Allantois in Man " (*' Ueber die ADan- 
tois des Menschen.**— "Archiv fiir Anat. n. Physiol.," 1875, p. 215, 
Plate VI.). 

107 (i. 400). The navel-cord (ftmicuhu umbilicalis), like 
the placenta, is an organ shared by Man exclusively with Pla- 
cental Animals. Cf . Chap. XIX. pp. 155-168, and Figs. 200, 201. 
On the more minnte structure of this organ, and on the special 
features of the embryonic blood-circulation, cf. Kolliker, " His- 
tory of the Evolution of Man.*' 2nd edition, 1876, pp. 319-363. 

108 (i. 401). The Kenogeny of Man. In pointing out the 
phylogenetic significance of the separate incidents and periods of 
human germ-history, and in explaining them by reference to cor- 
responding processes and stages in the tribal history of our animal 
ancestors, we must always bear in mind that in Man, as in all 
higher animals, the original palingenetic cause of germination 
has undergone much kenogenetic modification in consequence oi 
many adaptations to the very various conditions of embryonic 
life, that it has thus been much violated and contracted. The 
higher the organism develops, the more are especially these 
earliest stages of evolution abbreviated. 

109 (L 404). The sections of human germ-history, of which 
only four larger and ten smaller are mentioned here in reference 
to their phylogenetic significance, allow of much more division 
if their comparative Ontogeny is minutely examined. This 
phylogenetic significance may also be very well explained with 
fitting reference to kenogenetic displacements in place and time 
(voL L p. 13). 

110 (i. 405). Figures of human embryos in all stages of 



s 
HOTE& 479 

^rm-hif?tory were given in very beantifnl detail by M. P. Erdl 
thirty years ago : " The Evolution of Man, and of the Chick in 
the Egg" ("Die Entwickelung des Menschen, nnd des Hiihnchens 
imEi." Leipzig, 1845). 

111 (i. 409). Fritz Miiller, "Fiir Darwin." Leipzig, 1864. 
A very excellent little book, in which the modification of the 
fundamental law of Biogeny (with reference to the Phylogeny of 
Crustacea) are explained for the first time. 

112 (i. 413). The Method of Phylogeny is of the same 
morphological value as the well-known method of Geology, and 
may, therefore, claim exactly the same scientific acceptation. 
Cf. the excellent discourse by Eduard Strasburger, " On the 
Importance of Phylogenetic Methods in the Study of Living 
Beings." — '* Jenaiache Zeitschrift fiir Naturwissenschaft," 1874, 
rol. viii. p. 56. 

113 (i. 415). Johannes Miiller, " On the Structure and Yital 
Phenomena of Arwpliioxus ZanceoZaf^^s."— Transactions of tlir 
Berlin Academy, 1844. 

114 (i. 415). Recent works on the Amphioxus. W. Rolpl) 
and B. Ray Lankester especially have recently added to our 
knowledge of the organology of the Amphioxus, Wilhelm Miiller 
and P. Langerhans to that of its histology. The literature of 
this enbject is fully represented by W. Rolph, in his "Researches 
into the Structnre of the Amphioxns " (" Untersuchungen iiber 
den Ban des Amphioxns." — "Morpholog. Jahrb.," vol. ii. p. 87, 
Plates V. and YII.), and in P. Langerhans, " On the Anatomy of 
the Amphioxus" ("Zur Anatomie des Amphioxus." — *'Archiv. 
fur Mikr. Anat.," vol. xii. p. 290, Plates XII.-XV.). 

115 (i. 416). Acrania and Craniota. The separation of 
Vertebrates into Skull-less Animals {Acrania) and Sknllod 
Animals (Craniota), which I first indicated in 1866 in my 
" Generelle Morphologic," appears to me absolutely essential for 
the phylogenetic explanation of the Vertebrate-tribe. 

116 (i. 428). Max Schultze, "History of the Evolution of 
Petromyzon" ("EntwickelungsgeschichtevonPe^omi/2(w." Haar- 
lem, 1856), The Ontogeny of the Hags, which promises very 

anportant results, is yet, nnfortnnately, entirely nnknovni. 
64 



49o Nona 

117 (i. 450). Savignj, ** M^moiros but les Animanr lanfl 
Vert^bree/* Vol. ii, Ascidics, 1816. Giard, " Recherchea enr 
les Synascidies." — "Archives do Zoologie Experimentale/'Tol. i., 
1872. 

118 (i. 436). Syn-aacidia and Echinoderms. The Corm-theoiy 
of Echinoderms, which I explained in 1866 (" Generelle Mor- 
phologie/* vol. ii. p. liiii), and which has been much attacked as 
" paradoxical," is as yet the sole theory attempting the genetic 
explanation of this remarkable gronp of animals. 

119 (i. 442). Kowalevsky, "History of the Evolution of the 
Amphioxus and of Simple Ascidians" (" Memoires de I'Acad. de 
S. Petersbourg." 7 Serie. Tom. x. and xi. 1867-8). 

120 (i. 450). The metameric structure of the Amphioxus 
\v'hich is indicated in its nerve and muscle systems, undoubtedly 
sliows that the notochord exists in Vertebrates previous to their 
metameric structure, and consequently that it is inherited from 
nnarticulated Chorda Animals. 

121 (i. 454). The Metamorphosis of the Amphioxus, through 
which the larva passes into the adult form, is not yet fully 
known in all its details. This does not, however, affect the 
extraordinarily important bearing of the thoroughly known, 
earliest incidents in its germination on the palingenesis of Verte- 
brate*. 

122 (i. 465). Fertilization of Ascidia (Phallusia mammillata), 
Eduard Strasburger, " On Cell-structure and Cell-dirision, with 
Studies of Fertilization." 2nd edition. Jena, 1876, p. 306, 
Plate VIII. 

123 (i. 462). Kupffer. The tribal relation of Ascidia to 
Vertebrates ("Archiv fur Mikros. Anat.," 1870, vol. vi. pp. 
115-170). Oscar Hertwig, " Researches into the Structure and 
Evolution of the Cellulose Mantles of Tunicata " (" Untersu- 
chungen uber den Bau und die Entwickelung des Cellulose- 
Mantels der Tnnicaten"). Richard Hertwig, "Contribution to 
Knowledge of Ascidian Structure " (" Beitrage zur Kenntniss 
des Baues der Ascidien." — " JenaiAche Zeitschrift fur Naturwis- 
•enschaft," 1873, vol. vii.). 



NOTES. 4S1 

124 (i. 464). The Pliylogenetic Importance of the Amphi- 
oxoB cannot be too highly insisted on. Without knowledge of 
its Anatomy and Ontogeny, the origin of Vertebrates would be 
entirely dubious, and their descent from Worms would appear 
incredible. 

125 (i. 467). The Ontogenetic Cell-pedigree, as it is repre- 
sented, with reference to the Amphioius, in Table XI., probablj 
holds good, in its most important features, for all Vertebrates, 
and, therefore, also for Man. For, more than any other form, 
the Amphioxus by strict Heredity has accurately retained its 
Palingenesis. This histogenetic cell-pedigree is apparently well 
established as regards most and the chief features ; on the other 
hand, it yet appears doubtful with regard to the origin of the 
primitive kidneys, the testes, and ovaries. 

126 (ii. 4). Milne-Edwards, "Le9on8 sur la Physiologic 
Comparee," vol. ix. 

127 (ii. 6). Eternity of Organic Life. According to the 
monistic view, organic life is a further form of evolution of the 
inorganic word-processes, and had a beginning in time on our 
planet. In opposition to this, A. Fechner, among others, in his 
" Thoughts on the Creation and Evolution of Organisms," has 
stated certain opposed " kosmorganic pl^-ntasys " which appear 
entirely irreconcilable with the ontogenetic facts given here. 

128 (ii. 18). Bemhard Cotta (" Geologic der Gegenwart," 
1866; 4th edition, 1874) and Karl Zittel("Aus der Urzeit;" 
Miinchen, 1875, 2nd edition) have made some excellent remarks 
on the duration and the whole course of the organic history of 
the world. 

129 (ii. 21). August Schleicher, "The Darwinian Theory 
and Philology " ( " Die Darwin'sche Theorie und die Sprach- 
wissenschaft." Weimar, 1863. 2nd edition, 1873). 

130 (ii. 25). At first sight, most polyphyletic hypotheses 
appear more simple and easy than do monophyletic, but the 
former always present more difficulties the more they are 
oonsidered. 

X^X (ii. 25)« Those physiologists who desire an experi> 



4^2 NOTEa 

mental proof of tlie theory of descent, merely thereby prove theif 
extraordinary ignorance of the morphological scientific facts re- 
lating to this matter. 

132 (ii. 30). Spontaneous generation. — " Generelle Mor- 
phologic," vol. i. pp. 167-190. "Monera and Spontaneous Gene- 
ration." — "Jenaische Zeitschrift fur Naturwissenschaft," 1871, 
vol. vi. pp. 37-42. 

133 (ii. 33). The Absence of Organs in Monera. In saying 
that Monera are " organisms without organs," we understand the 
definition of organs in a morphological sense. In a physiological 
sense, on the other hand, we may call the variable plasson- 
processes of the body of the Moneron the " pseudojjodia " organs. 

134 (ii. 36). Induction and Deduction in Anthropogeny. 
"Generelle Morphologic," vol i. pp. 79-88; vol. ii. p. 427. 
" History of Creation," vol. ii. p. 357. 

135 (ii. 42). Animal Ancestors of Man. The number of 
species (or, more accurately, form-stages, which are distinguished 
as " species ") must, in the human ancestral line (in the course of 
many millions of years !), have amounted to many thousands ; 
the number of genera to many hundreds. 

136 (ii. 47). Following Elsberg, we give the name of "plas- 
tidules" to the "molecules of plasson," to the smallest like parts 
of that albuminous substance which, according to the " plastid- 
theory," is the material substratum of all the active phenomena 
of life. Cf. my work on " The Perigenesis of Plastidules " 
(" Perigenesis der Plastidule oder Wellenzeugung der Lebens- 
theilchen." Berlin, 1876). This is an attempt to explain 
mechanically the elementary processes of evolution. 

137 (ii. 49). Batliybius and the free protoplasm of ocean 
depths. Cf. my " Studies on Monera and other Protista." 
Leipzig, 1870, p. 86. The most recent observations on living 
Bathybius are those of Dr. Emil Bessel, who found this form on 
the coast of Greenland (in Smith's Sound), at a depth of about 
550 ft. He noticed very active amoeboid movements in them, 
as well as the assumption of foreign particles (carmine, etc.). 
" It consists of nearly pure protoplasm, tinged most intensely by 



NOTES. 4S3 

a solution of (jarmine in ammonia. It contains fine gray gi*anulea 
of considerable refracting power, and besides the latter a great 
number of oleaginous drops, soluble in ether. It manifests very 
marked amoeboid motions, and takes up particles of carmine, etc." 
— Packard, " Life Histories of Animals, including Man." New 
York, 1876. 

138 (ii. 50). The Philosophical Importance of Monera in 
explaining th.e most obscure biological questions cannot be 
sujEciently emphasized. Monograph of Monera. — " Jenaische 
Zeitschrift fur Naturwissenschaft," vol. iv., 1868, p. 64. 

139 (ii. 54). The Nature and Significance of the Egg- cell can 
only be philosophically understood by means of phylogenetic 
examination. 

14j0 (ii. 58). Synamoeba. Cienkowski, "On the Structnre 
and Evolution of Labvrinthula " ("Uber den Ban und die Entwic- 
kelung der Labyrinthuleen."^Arch. fiir Mikrosk. Anat., 1870, 
vol. iii. p. 274). Hertwig, " Microgromia Socialis." — Thid. 

141 (ii. 61). Catallacta, a new Protista-group (Magosphcera 
planula). See " Jenaische Zeitschrift fiir Naturwissenschaft," 
vol. vi., 1871, p. 1. 

142 (ii. 66). Haliphysema and Gastrophysema. Extant 
Gastraeads. See " Jenaische Zeitschrift fiir Naturwissenschaft," 
vol. xi., 1876, p. 1, Plates I.-YI. 

143 (ii. 70). The five first stages in the evolution of the 
animal body, which are compared in Table XVII., and which 
are common to Man and all higher Animals, are established 
beyond all doubt as existing in the Ontogeny of most extant 
animals. As Comparative Anatomy shows that corresponding 
form-stages yet exist in the system of the lower animals, we 
may assume, in accordance with the fundamental law of Biogeny, 
that similar forms existed phylogenetically as most important 
ancestral forms. 

144 (ii. 77). On the distinction of the axes, and on the 
geometric outline of the animal body, see " Promorphologie " 
(" Generelle Morphologic," vol. i. pp. 374-574). 

145 (ii. 87). The hermaphrodite structure of our ancestral 



4^4 NOTES. 

series was perhaps transmitted from the Chorda Animals even as 
far as the lower stages of Vertebrate ancestors. Cf . Chapter XXV. 

146 (ii. 89). I am inclined to regard the Appendicularia as 
living Chorda Animals of the present day; they are the only 
Invertebrates permanently possessing a notochord, and thus, as 
by many other peculiarities, distingnished from genuine Tuni- 
cates. 

147 (ii. 105). Metamorphosis of Lampreys. That the blind 
Ammocoetes change into Petromyzon was known two hundred 
years ago (1666) to the fisherman Leonhard Baldner of Stras- 
burg ; -but this observation remained unrecognized, and the 
modification was first discovered by August Miiller in 1854 
(" Archiv fur Anat.,'* 1856, p. 325). Cf. Siebold, " The Fresh- 
water Fishes of Central Europe** ("Die Siisswasserfische von 
Mittel-Europa," 1863). 

148 (ii. 114). Selachii as Primitive Fishes. The old disputes 
as to the systematic position and kindred of Selachii were first 
definitely settled by Gegenbaur, in the introduction to his classical 
work on " The Head-skeleton of Selachii." 

149 (ii. 118). Gerard Krefft, "Description of a Gigantic Am- 
phibian ; ** and Albert Giinther, " Ceratodus, and its Systematic 
Position." — "Archiv fiir Naturgeschichte," 37, 1871, vol. i. p. 
321 ; also "Phil. Trans.," 1871, Part II. p. 511, etc. 

150 (ii. 129). The duration of metamorphosis of Amphibia 
varies much in the different forms of Frogs and Toads, the whole 
forming a complete phylogenetic series from the original, quite 
'complete form, to the later, much shortened and vitiated heredity 
of modification. 

161 (ii. 129). " AH the histological features of the Land 
Salamander (Salamandra maculata) force the impression that it 
belongs to an entirely different epoch of terrestrial life than that 
of the Water Salamander {Triton), externally so similar." — Robert 
Remak (" Entwickelung der Wirbelthiere," p. 117). 

152 (ii. 130). Siredon and Amblystoma. Very various views 
have lately been expressed as to the phylogenetic significance to 
be attributed to the much- discussed modification of the Mexican 



NOTES. 485 

Axolotl into an Amblystoma. Of. on this Bnbject especially 
August Weismann, in " Zeitsch. fur wissenscli. Zoologie," rol. 
XXV., Sup., pp. 297-334. 

153 (ii. 131). The Leaf-frog of Martinique (Hylodes rruur- 
Hnicensis) loses its gills on the seventh day, its tail and yelk-sao 
on the eighth day of egg-life. On the ninth or tenth day after 
fertilization the complete frog emerges from the egg. — Bavay, 
**Sur I'Hylodes Martinicensis et ses Metamorphoses." "Journal, 
de Zool. par Q-revais," vol. ii. 1873, p. 13. 

154 (ii. 133). " Homo diluvii testis " = Andrias Scheuchzeri. 
•* Sad bone of an ancient evil-doer ; Soften, stone, the heart of 
the new children of evil " (Diaconus Miller). Quenstedt. 
"Formerly and Now" (" Sonst und Jetzt," 1856, p. 239). 

155 (ii. 133). The Amnion-structure of the three higher 
Vertebrate-classes, wanting in all lower Vertebrates, has no 
connection with the similar, but independently acquired Amnion- 
structure (analogous, but not homologous) of higher Articu- 
lated Animals (Arthropoda). 

156 (ii. 138). The former existence of a Protamnion, the 
common parent-form of all Amniota, is undoubtedly shown by 
the Comparative Anatomy and Ontogeny of Reptiles, Birds, and 
Mammals. No fossil remains of such a Protamnion have, how- 
ever, yet been discovered. They must be sought in the Permian 
or Carboniferous formation. 

167 (ii. 147). The former organisation of the Promammalia 
may be hypothetically reconstructed from the Comparative 
Anatomy of the Salamander, Lizards, and Beaked Animals 
(OmithorhyncJiics). 

158 (ii. 153). The Didelphic ancestors of Man may have been 
externally very different from all known Pouched Animals (Jfar- 
awpialia)^ but possessed all the essential internal characters of 
Marsupialia. 

159 (ii. 163). The phylogenetic of the Semi-apes, as the 
primaeval placental parent-group, is not influenced by our ignor- 
ance of any fossil Prosimise, for it is never safe to estimate 
palaBontological facts as negative, but only as 'positive. 



4^6 NOTES. 

160 (ii. 168). On the stnicture of the Decidna very variotis 
theories have been given. Cf . Kolliker, " History of the Evolution 
of Man " (" Entwickelungsgeschichte des Menschen." 2nd 
edition, 187] , pp. 319-376). Ercolani (Giambattista), " Snl pro- 
cesso formativo della placenta." Bologna, 1870. "Le glandole 
otricolari derntero." Bologna, 1868, 1873. Huxley, "Lectures 
on the Elements of Comparative Anatomy," 1864, pp. 101-112. 

161 (ii. 172). Huxley, " Anatomy of Vertebrates," 1873, 
p. 382. Previously Huxley had separated the " Primates " into 
seven families of nearly equal systematic value. (See "Man's 
Place," etc., p. 119.) 

162 (ii. 179). Darwin. Sexual selection in Apes and Msa. — 
" Descent of Man," vol. ii. pp. 210-355. 

163 (ii. 180). Man-like Holy Apes. Of all Apes, some Holy 
Apes (^Semnojpithecms) most resemble Man, in the form of their 
nose and the character of their hair (both that on the head and 
that on the beard). — Darwin, " Descent of Man," vol. i. p. 335 ; 
vol. ii. p. 172. 

164 (ii. 182). Friedrich Muller (" AUgemeine Ethnographie." 
Vienna, 1873, p. 29), on the supposed age of man. Families of 
languages (pp. 5, 15, etc.). 

165 (ii. 183). The plate (XV.) representing the migrations, 
given in the " History of Creation," merely claims the value of 
a first attempt, is an hypothetic sketch, as I there expressly said, 
and as, in consequence of repeated attacks, I must here insist. 

166 (ii. 201). The Leather-plate. The phylogenetic distinction 
of a special leather-plate, the outermost lamella separating from 
the skin-fibrous layer, is justified by Comparative Anatomy. 

167 (ii. 204). Milk-glands. Huss, "Contributions to the 
History of the Evolution of the Milk- glands" ("Beitrage zur 
Entwickelungsgeschichte der Milchdriisen ") ; and Gegenbaur, 
" On the Milk-gland Papillae " (" Jenaische Zeitschrift fiir 
Natorwissenschaft," 1873, vol. vii. pp. 176, 204). 

168 (ii. 208). On the hairy covering of Man and Apes, see 
Darwin, "Descent of Man," vol. i. pp. 20, 167, 180; vol. ii. 
pp. 280, 298, 335, etc. 



NOTES. 487 

169 (li. 217). Dorsal side and ventral sides are homologous 
in Vertebrates, Articulated Animals (Arthropoda), Soft-bodied 
Animals {Mollusca), and Worms, so that the dorsal marrow and 
the ventral marrow are not comparable. Cf. Gegenbaur, "Morph. 
Jahrbuch," vol. i. pp. 5, 6. 

170 (ii. 228). The unknown ontogenetic origin of the sym- 
pathetic nerve-system mnst probably, for phylogenetic reasons, 
be songht chiefly in the intestinal layer, not in the skin-layer. 

171 (ii. 248). On the cavities connected with the nose, see 
Gegenbaur, " Elements of Comparative Anatomy," p. 580. 

172 (ii. 260). The analogies in the germination of the higher 
sense organs were rightly grasped even by the earlier natural 
philosophers. The first more accurate sketches of the very 
obscure germ-history of the sense-organs, especially of the eye 
and ear, were given (1830) by Emil Huschke, of Jena (Isis, 
Meckel's Archiv, etc.). 

173 (ii. 265). Hasse, "Anatomical Studies" (** Anatomische 
Studien "), chiefly of the organ of hearing. Leipzig, 1873. 

174 (ii. 269). Johannes Rathke, " On the Gill- apparatus and 
the Tongue-bone " (" Ueber den Kiemen-apparat und des 
Zungenbein," 1832). Gegenbaur, " On the Head-skeleton of 
Selachii," 1872. (See note 124.) 

175 (ii. 272). On the Rudimentary Ear-shell of Man, cf. 
Darwin, "Descent of Man," vol. i. pp. 17-19. 

176 (ii. 276). Scarcely anywhere does Comparative Anatomy 
prove its high morphological value as with reference to the 
skeleton of Vertebrates : in this matter it accomplishes much 
more than Ontogeny. There is all the more reason to insist on 
tliis here, as Goette, in his gigantic history of the evolution of 
Bombinator, has recently denied all scientific value to Com- 
parative Anatomy, and asserted that Morphology is explained 
solely by Ontogeny. Cf . my " Aims and Methods of the Recent 
History of Evolution " (" Ziele und Wege der heutigen Ent- 
wickelungsgeschichte," 1875, p. 52, etc.). 

177 (ii. 283). The Human Tail, like all other rudimentary 
organa, is very variable in point of size and development. In 



488 NOTES. 

rare cases it remains permanently, projecting freely : nsnally it 
disappears at an early period, as in Anthropoid Apes. 

178 (ii. 284). On the Number of Yertebrss in different Mam- 
mals, cf. Cuvier, "Lemons d* Anatomic Comparee." 2nd edition, 
tome i., 1835, p. 177. 

179 (iL 293). On the earHer Sknll-theory of Goethe and Oken, 
cf . Virchow, " Goethe as a Naturalist " (" Goethe als Natur- 
forscher," 1861, p. 103). 

180 (ii 295.). Karl Gegenbaur, "The Head-skeleton of 
Selachii" ("Das Kopfskelet der Selachier"). As the foundation 
of a study of the head-skeleton of Vertebrates (1872). 

181 (ii. 301). Karl Gegenbaur, " On the Archipterygium." 
— " Jenaische Zeitschrift fiir Naturwissenschaft," vol. viL 1873, 
p. 131. 

182 (ii. 304). Gegenbaur, " Researches into the Comparative 
Anatomy of Vertebrates" (" Untersuchungen zur Vergleichen- 
den Anatomic der Wirbelthiere "). Part I. Carpus and Tarsus 
(1864). Part II. The shoulder girdle of Vertebrates. Pectoral 
fins of Fishes (1866). 

183 (ii. 305). Charles Martins, "Nouvelle comparaison des 
membres pelviens et thoraciques chez I'hommc et chez les 
mammiferes." — "Memoircs dc TAcad. de Montpellier," vol. iii 
1857. 

184 (ii. 308). Ossification. Not all bones of the human bod} 
arc first formed of cartilage. Cf. Gegenbaur, " On Primary and 
Secondary Bone-formation, with special reference to the Pri- 
mordial Skull Theory." — " Jenaisch. Zeitschrift fiir Natur- 
wissenschaft," 1867, vol. iii. p. 54. 

185 (ii 308). Johannes Miiller, "Comparative Anatomy of 
Myxinoides." — " Transactions of the Berlin Academy," 1834-1842. 

186 (ii. 314). The Homology of the Primitive Intestine and 
the two primary germ-layers is the postulate for morphological 
comparison of the various Metazoa-tribes. 

187 (ii. 322). In the Evolution of the Intestine, Amphibia and 
Gunoids have, by heredity, retained the original Craniota-form 
more accurately than have Selachii and Osseous Fishes (Teleotlei). 



NOTES. 489 

The palir genetic germination of Selachii has been nmch altered 
by kenogenetic adaptations. 

188 (ii. 323). On the Homology of Scales and Teeth, cf. 
Gegenbanr, " Comparative Anatomy " (" Grundriss der vergl. 
Anatomie,'* 1874, pp. 426, 582) ; also Oscar Hertwig, " Jenaische 
Zeitschrift fiir Naturwissenschaft," 1874, vol. viii. On the 
important distinction of homology (morphological resemblance) 
and Analogy (physiological resemblance), see Gegenbaur, as 
above, p. 63; also my " Generelle Morphologic, '* vol. i. p. 313. 

189 (ii. 337). Wilhelm Miiller, "On the Hypobranchial 
Groove in Tunicates, and its Presence in the Amphioxus and 
Oyclostomi." — "Jenaische Zeitschrift fur Naturwissenschaft," 
1873, vol. viii. p. 327. 

190 (ii. 358). The Nerve- mnscnlar Cells of the Hydra throw 
the earliest light on the simultaneous, phylogenotic diSerentiation 
of nerve and muscle tissue. Cf. "Klemenberg, Hjdra." Leipzig, 
1872. 

191 (ii. 383). The germ-history of the human heart accurately 
reproduces in all essential points its tribal history. This paliu- 
genetic reproduction is, however, much contracted in particular 
points and vitiated by kenogenetic modifications of the origiual 
course of evolution, displacements partly in time, partly in place, 
which are the result of embryonic adaptations. 

192 (ii. 383). On the Special Germ-history of the Hnman 
vascular system, cf. Kolliker, "History of the Evolution of Man" 
("Bntwickelungsgeschichte des Menschen." 2nd edition, 1876) ; 
also Rathke's excellent work on Ontogeny. 

193 (ii. 387). The Homologies of the Primitive Organs, as 
they are here provisionally described in accordance with the 
Qtistreea- theory (note 24), can only be established by further co- 
operation between Comparative Anatomy and Ontogeny. Cf. 
Gegenbaur on Comparative Anatomy (" Grundriss der verglei- 
chenden Anatomic "). 

194 (ii. 390). The Mechanism of Reproduction. As the 
functions of reproduction and of heredity, connected with re- 
production, are referable to growth, so the former as well as tho 



490 NOTsa 

latter are finally explicable as the results of the attraction and 
rejection of homogeneous and heterogeneous particles. 

195 (ii. 397). Eduard van Beneden, " De la Distinction origi- 
nelle du Testicule et de I'Ovaire." Brussels, 1874. 

196 (ii. 399). On the Original Hermaphrodite Structure of 
Vertebrates, cf. Waldeyer, " Ovary and Egg " (" Eierstock und 
Ei," 1872, p. 152) ; also Gegenbaur (*' Grundriss der vergleichen- 
den Anatomie," 1874, p. 615). On the origin of the eggs from the 
ovary-epithelium, cf. Pfliiger, " On the Ovaries of Mammals and 
Man" ("Die Eierstocke der Saugethiere und des Menschen,*' 
1863). • 

197 (ii. 423). On the special germ-history of the urinary and 
sexual organs, cf. Kolliker, " History of the Evolution of Man." 
On the homologies of these organs, see Gegenbaur (" Grundriss 
der vergleichenden Anatomie," 1874, pp. 610-628). 

198 (ii. 448). Wilhelm Wiindt, "Lectures on the Human and 
Animal Mind" (" Vorlesungen iiber die Menschen- und Thier- 
seele." 1863). W. Wundt, "Outlines of Physiological Psy- 
chology" ("Grundziige der Physiologishen Psychologie," 1874). 

199 (ii. 457). On Active (actual) and Latent (preteritial) 
forces, cf. Hermann Helmholtz, " Interoperation of Natural 
Forces " (" Wechselwirkung der Naturkrafte," Part II., 1871). 

200 (ii. 457). "Anthropology as Part of Zoology." — " Generello 
Morphologie," voL iL p. 4!32. ** History of Creation,*' voL L 7 j 
vol. ii d47. 



INDEX. 



AcAiEPH^, u. 73, 92 

Acoelomi, ii. 75, 92 

Acorn- worms, ii. 86 

Acrania, i. 116 ; ii. 97 

Adam's apple, ii. 336 

Adaptation, i. 158 

After-birth, i. 400 

Agassiz, thoughts on creation, i. 116 

Air-tube (trachea), ii. 330, 333 

Alali, ii. 182 

Allantois, i. 380 ; ii. 135, 411 

Alluvial period, ii. 12 

Amasta, ii. 146, 204 

Amnion, i. 314, 386 

animals, ii. 120, 133 

sheaths of, i. 387 

water, i. 314 

Amniota, ii. 120, 133 
Amoeba, i. 142 ; ii. 152 

false feet of, i. 142 

Amoeboid egg-cells, i. 144 ; ii. 53 

movements, i. 142 ; ii. 53 

states, ii. 56 

Amphibia, ii. 120, 122 
Amphigastrula, i. 200, 241 
Amphigonia, i. 160 
Amphioxus, i. 413 ; ii. 98 

blastula of, i. 443 

body-form of, i. 417 

cells of, their pedigree, 

i. 467 

chorda of. i. 417 

distribution of, i. 416 

— — gastrula of, i. 444 

"■ — germ-layers of, i. 447 



Amphiozns, mednllarj t«be of, L 418 
place of, in natural 

system, i. 416 

sexual organs of, i. 425 

— side canals of, i. 423 

significance o^ L 254, 

427 
Attvphirhina, ii. 97, 101 
Analogy, ii. 412 
Anaraniay ii. 97, 120 
Ancestral series of man, ii. 44, 184 
Animalcnlists, i. 37 
Animal germ-layer, i. 194, 327 



organs, ii. 192, 194 



Anorgana, i. 156 ; ii. 30 

Anthropocentric conception, ii. 457 

Anthropoids, ii. 177, 189 

Anthropolithic epoch, ii. 11, 16 

Anthropozoic periods, ii. 12, 17 

Antimera, i. 257 

Anus, i. 339 j ?i. 323, 345 

Anus-groove, i. 339 

Anvil (Incus of ear), il 261, 268 

Ape-men, ii. 44, 181 

Apes, ii. 165, 189 

eastern, ii. 172, 189 

flat-nosed, ii. 172, 189 

narrow- nosed, ii. 172, 189 

question as to descent of, ii 

165, 441 

tailed, ii. 172, 189 

western, ii. 172, 189 

Aorta, i. 265 ; ii. 378 

roots of, ii. 375 

— — ^ stem of, ii. 375 
Aortal arches, ii. 375, 378 
Appendiculariot i. 459 ; ii. 90 



492 



INDEX. 



Arehelnwnthes, ii. 76 
Archigastrula, i. 198, 241 
Archilithic epoch, ii. 9, 19 
Arehipterygiv/m, ii. 301 
Arohizoio periods, ii. 9, 11 
Area gertninativa, i. 292 

opaca, i. 296 

pellucida, i, 296 

Arietotle, 1. 27 ; ii. 368 

epigenesis, i. 29 

heart formation, ii. 368 

 his history of eyolution, 
i. 27 
Ann, lower, ii. 278, 804 

upper, ii. 278, 304 

ArtericB omphalo-mesenteriecOf i. 895 

vmbilicales, i. 400 

vertehrales, i. 396 

vitelUncB, 1. 395 

Arteries, i. 393 
Artery-arohes, ii. 377 

stalk, ii. 380 

Arthropoda, ii. 92, 94 
Articulated animalB, ii. 92, 94 
Articulation in man, i. 346 
Ascidia, i. 429 ; ii. 90 

ilastula of, L 455 

chorda of, i. 456 

— — communities of, i. 455 

gastrula of, i. 455 

gill-sac of, i. 431 

heart of, i. 433 

homologies of, i. 465, 466 

intestine of, i. 432 

mantle of, i. 430, 461 

medullary tube of, i. 458 

sexual organs of, L 434 

tail of, i. 456 

AsoulOf ii. 68 
Atrium, ii. 874, 881 
Auditory nerve, ii. 262 
— — — organ, ii. 260 

passage, ii. 269 

vesiclei, ii. 262 

Auricular processes of heart, iL 881 
Axes of the body, i. 255 ; ii. 77 
Axial cord, L 301 

rod (notochord), i. SOS 

skeleton, u. 280, 899 

Axis-plate, i. 299 

iL im 



B 



Baeb, Karl Ernst, i. 60 

his germ-layer theory, 1. 61 

his law, i. 58 

' life of, i. 52 

on the bladder.like outline, 

ii. 62 
 on the human egg, L 55 ; ii, 
424 

on the notochord, i. 65 

on type theory, L 64 

Balanoglo88U8, ii. 85 

Bathybius, ii. 49 

Batrachia, ii. 131 

Bats, ii. 169, 187 

Beaked animals, ii, 147, 187 

Bell-gastrula, i. 198 

Bilateral outline, i. 257 ; ii. 74 

Bimana, ii. 169 

Biogeny, L 24 ; ii. 434 

fundamental law of, i. 6, 

24 ; ii. 434 
Birds, ii. 120, 138 

gastrula of, i. 223 

Bischoflf, Wilhebn, i. 59 
Bladder-gaetrula, i. 229, 241 
Blastcea, ii. 31 
BlastocoBloma, i. 189 
Blastoderma, i. 189 
Blastodiscus, i. 227 
Blastogeny, i. 24 
Blastophylla, i. 196 
Blastophyly, L 24 
Blastosphcera, i. 191 
Blastula, i. 191, 242 
Blind-intestine, ii. 330, 348 
Blood-cells (corpuscles), i. 169} M. 
366 
  relationship, i. 112 

vessels, ii. 870 

Bloodless worins, ii. 76 
Bonnet, i. 40 
Brain, i. 212, 232 

bladders of, i. 348 f fi. 114 

parts of, ii. 212 

skull of, ii. 29S 

Breast>body, ii. 288 

bone, ii. 282 

 i o»vity, i. 261 

ii. Ml 



INDEX 



493 



Bndding (gemmation), ii. 891 
Bulhus arteriosv^, ii. 374 
BuUms oculif ii. 250 



Cjeicolithic epoch, ii. 11, 16 
Csenozoic period, ii. 15, 19 
Calf -bone, ii. 278, 304 
Cambrian period, ii. 9, 19 
Canalis auricularis, ii. 381 
Carboniferous period, ii. 10, 19 
Cardinal veins, i. 391 
Carpus, ii. 278 
CatarhincB, ii. 176, 189 
Catastrophes, theory of, i. 76 
Causae eficientes, i. 16, SO ; ii. 455 

finales, i. 16, 80 ; ii. 455 

Cavum tywpani, ii. 261, 270 
Cell-division, i. 124 

kernel (nucleus), L 126 

state, i. 124 

substance, i. 125 

Cells, i. 125 

female, i. 171 ; ii. 392 

male, i. 171 ; ii. 392 

theory of, L 60, 121 

Central heart, ii. 120 

medulla, ii. 210, 232 

nerve-system, ii. 210 

skeleton, ii. 280, 299 

« Centre of sight," ii. 252 
Ceratod'us Fosteri, ii. 119 
Cerehellwm, ii. 212, 232 
Cerehrvm, ii. 212, 232 
Cetacea, ii. 187 
Cetomorpha, ii. 160, 187 
Chalk period, ii. 14, 19 
Chalk-sponges, i. 117 
Chick, importance of, L 31 
Chimpanzee, ii. 178, 180 
Chorda animals, ii. 84, 87 

dwsaUa, i. 255, 301 

sheath, ii. 286 

tissue of, ii. 286 

vertehralis, i. 255, 301 

Chordoma, i. 84, 87 
Chorioidea, ii. 252, 258 
Chorion, i. 387 ; ii. 158 

frondosu/m, ii. 160 

I«v«, ii, 160 



Chorion, smooth, ii. 160 

tufted, ii. 160 

Chorology, i- 113 
Chyle vessels, ii. 374 
Cicatricula, i. 138 
Circulation in Amphioxus, i. 

Ascidia, i. 433 

Fishes, ii. 375 

germ-area, i. 397 

Mammals, ii, 378 

Clavicula, ii. 278, 304 
Cleavage cells, L 185 

forms of, i. 242 

of e^^, i. 185, 241 

partial, of bird's egg, L 224 

rhythm, i. 243 

1 superficial, i. 200, 241 

unequal, i. 200, 241 

Clitoris, ii. 423, 431 
Cloaca, ii. 145, 418 
Cloacal animals, ii. 145, 187 
Coalescence, i. 164 

Coal period, ii. 11, 19 

Coccyx, n. 282 

Cochlea, iL 263, 268 

Coel&nterata, ii. 73 

Cceloma, i. 260 ; ii. 76 

Ccelomati, ii. 75, 92 

Columna vertehralis, i. 349 ; ii. 286 

Comparative Anatomy, i. 107, 245 

Concrescence, i. 164 

Conjunctiva, ii. 259 

Connective membrane of eye, ii, 261 

tissue, ii. 363 

Connectivum, ii. 361, 366 

Convolutions of brain, ii. 228 

Copulation organs, ii. 421 

Copulativa, ii. 421 

Coracoideum, ii. 278, 304 

Corium, ii. 200, 232 

Cormogeny, i. 24 

Cormophyly, i. 24 

Cornea, ii. 251, 258 

CostoB, ii. 278, 282 

Covering tissue, ii. 361 

Craniota, ii. 100, 120 

Crarwu/m, ii. 291 

Creation, i. 74, 79 ; ii, 188 

Crooked intestine, ii. 319, 880 

Cross-vertebrae, ii. 282 

Crystalline lens, ii. 253, 268 

Culture period, ii. 11 



494 



INDEX. 



Cnrres of embryo, i. 369 

Cutis, ii. 200, 232 

Cuvier, theory of cjatastropheg, i. 76 

theory of types, i. 57 

Cycloetoma, ii. 101, 120 
Cytods, i. 103 
Cytula, i. 176 
CytooocciiB, L 176 



Daxtov, i. 51 

Darwin, Charles, L 96 

descent of man, i. 103 

^ selection, theory of, i. 95 

Bemal selection, i. 103 

Erasmus, L 96 

Darwinism, i. 95 
Deoidua, ii. 161, 165 

animals, ii. 161 

Decidna^less animals, ii. 161 
Decidniata, ii. 161, 187 
Deduction, i. 104 ; ii. 37 
Degree of development, i. 58 
Derma, ii. 232 
Descent, theory of, i. 84 

of man, i. 104 

Devonian period, ii. 10, 19 
IHdeVphia, ii. 149, 187 
Differentiation, i. 152, 159 
Digestive intestine, ii. 330 
Digits, ii. 278 
Dilarial period, iu 12, 15 
Dipneosta, ii. 115, 120 
DuBOOgastmla, i. 219, 241 
Discoidal cleayage, i. 225, 242 
D»«eopIac««aaZ»a, ii. 162, 187 
Biscu* hla^odermicvis, i. 139, 226 
Doellinger, i. 50 
Dorsal fnirow, i. 302 

marrow, ii. 221 

— — — swellings, i. 303 
Donbla-breathers, ii. 117, 120 

nostrils, ii. 97, 101 

« Double-shield," i. 297 
Dualism, i. 17 ; ii. 456 
Dualistic philosophy, i. 17 
Ductut Qartneri, ii. 416, 431 

Mullen, ii. 415, 431 

Bathkei, ii. 415, 431 

WoljSHi, ii. 415, 431 

DysfcelMlogy, i. 109 



Eae, bonelets of, ii. 268 

labyrinth of, ii. 262, 268 

muscles of, ii. 271 

nerve of, ii. 266 

pouch {viriculus) , ii. 262 

sac (sacculus), ii. 262 

shell of, ii. 269 

snail of, ii. 263, 268 

trumpet, ii. 260 

vesicles, ii. 265 

wax, glands of, ii. 262 

Echidna, ii. 147 
Echinoderma, L 435 ; ii. 92 
Egg-cell, i. 132 

of Chick, i. 139 

Bird, i. 139 

Mammal, i. 137 

Man, i. 137 ; ii. 425 

sponge, i. 144 

cleavage, i. 185, 242 

holoblastic, i. 215 

human, i. 137 ; ii. 425 

membranes, i, 375 ; ii. 158 

meroblastic, i. 216 

Elbow, ii. 278, 304 
Elementary organism, i. 124 
Embryo of Vertebrates, i. 360 
Embryology, i. 3 
Empty intestine, ii. 319 
Encephalon, ii. 232 
Endoccelarium, ii. 366, 400 
Enteropneusta, ii. 86 
Entoderms, i. 206, 236 
Eocene period, ii. 11, 16 
Epidermis, ii. 200, 232 
Epididymis, ii. 417, 428 
Epigenesis, i. 39, 41 
Epigenesis, theory of, i. 39, 41 
Epithelial tissue, ii. 361 
Epithelium,, ii. 361, 366 
Epochs, duration of, ii. 3 
Evolution of forms, i. 19 

of functions, i. 19 

history of, i. 1, 24 

theory of, i. 34 

Excretory organs, i. 267 ; ii. 408 
Exoccelarium, ii. 369, 400 
EwedermQ, i. 195, 236 



iHDJUL 



495 



Extremitlee, ii. Ill, 806 
Eye, ii. 250, 258 

connective membrane of, ii. 

251 

lids, ii. 259 

netted membrane of, ii. 252, 

268 
— - ]»t>teotive membrane of, ii 251 
— — pupil of, ii. 250 

rainbow membrane of, ii. 252 

I rascular membrane of, ii. 252 
Twiclea, L S67 1 ii 263 



Fabbicitts ab Aquapindente, i. 81 
Face, development of, ii. 245, 846 

skull of, ii. 278, 294 

Fallopian canals, ii. 431 

hydatids, ii. 431 

Fatty layer of oorium, ii. 232 
Female breast, ii. 202 

cells, i. 171, 392 

Oqpnlatory organs, ii. 423 

excretory dncts, ii. 415, 431 

— — — — germ-glands, ii. 398 

germ-layer, ii. 398 

— — — milk glands, ii. 202 
— -^ phallus (Clitoris), ii. 428 
— — sexual organs, ii. 423 

sexual plate, iL 401 

uterus, ii. 417 

Femur, ii. 278, 304 
Fertilization, i, 169, 176 
Fibula, ii. 278, 304 
Fia, central ffod of, ii. 802 
Fin, rays of, ii. 302 

 skeleton of, ii. 808 
Final causes, i. 16 
Fingers, ii. 278 
Fishes, ii. 109, 120 

fins of, ii. Ill 

gastrula of, i. 219 

scales of, ii. 331 

Fire-digited foot, ii, 128 
Flat-worms, ii. 76 
Flesh, i. 259 
Flesh-kyer, i. 286 
Foot, ii. 170 
Flovoe and matter, ii. 466 

65 



Forces, active, 8. 487 

latent, ii. 457 

Formative functions, i. 16 

yelk, i. 216 

Forms, science of, i. 20 
Frog-Batrachia, ii. 181 
Frogs, ii. 131 

egg-cleavage of, i. 208 

' gastrula of, i. 207 

-  larva of, ii. 127 

metamorphosis of, iL 126 

Frontal process, ii. 244 
Functions of evolution, ii. 156 

science of, i. 19 

Funiculus genitalis, ii. 418 
umbiUcaUs, i. 883 ; ii. 16b 



e 

Gall-bladder, ii. 841 

ducts, ii. 341 

intestine, ii. 317, 380 

Ganoid Fishes, ii 112, 120 

Gartnerian duct, ii. 416, 431 

GastrcBa, i. 232 ; ii. 66 

theory of, i. 247 ; ii. 195 

Gastraeads, ii. 62, 70 

Gastrocystis, i. 291 

Qastrodiscus, i. 292 

Gastrula, i. 192 ; ii. 65 

Bell-, i. 198 

Bladder-, i. 200 

Disc-, i. 200 

Hood-, i. 200 

Gegenbaur, i. 108; ii. 96 

on Comparative Ana- 
tomy, ii. 96 

Gegenbaur on head-skeleton, ii. 29.3 

on theory of descent, 

i.108 

skull theory, ii. 293 

theory of limbs, ii. 299 

Oeneratio spontanea, ii. 30 

" Generelle Morphologie," i. 102 

Geological hypotheses, i. 410 

Germ, i. 3 

Germ-area, i. 292 

- dark, i. 297 

light, i. 297 



cavity, i. 189 
diao, i 189» 



496 



nmEx. 



Germ-epithellBm, ii. 401 

glands, ii. 398 

history, i. 6, 24 

layer, middle, i. 13 

membrane, i. 189 

membrane vesicle, i. 189 

plate, ii. 401 

point, i. 135 

shield, i. 297 

spot, i. 135 

yesicle, i. 179, 291 



Gibbon, ii. 178, 181 
Glacial period, ii. 11 
Glands of intestine, ii. 330 

skin, i. 201 

Giant phalli, ii. 422 
Qhymeruli renales, ii. 407 
Onathostomi, ii. 109 
Goethe, Wolfgang, i. 88 

his skull theory, ii. 293 

morphology, i. 88 

on metamorphosis, i. 90 

on reason, ii. 453 

on specification, i. 90 

Goette, Alexander, i. 65 
Gonades, ii. 398 
Gonochorisrmis, ii. 69, 396 
Gonophori, ii. 402 
Gorilla, i. 178, 180 
Graafian follicles, ii. 424 
GvhemaeuluMi Hv/nterif ii. 4i31 



Hai«, ii. 205, 232 
Hair-animals, ii. 205 
Hairy covering, ii. 206 
Haliph/ysema, ii. 66 
Haller, Albrecht, i. 38 
Hand, ii. 169 

skeleton of, ii. 302 

Hare-lip, ii. 246 
Harvey, i. 31 
Head-cap, i. 386 

marrow, ii. 210 

plate, i. 335 

ribs, ii. 298 

sheath, i. 387 

Heart, auricle of, ii. 381 

-  ftorioalar procesgei of, ii. 






381 



Heart oarity, i. 894 

development of, ii. 88S 

human, ii. 379, 382 

— ^— — mesentery, i. 394 

ventricle of, iL 381 

Heopitheciy Li. 172 

Heredity, i. 161 

vitiated, i. 408 

Hermaphrodites, ii. 395 

Hermaphi-odite gland, ii. 401 

Vertebrates, ii. 4Ui 

Hermaphroditisrmis, ii. 69, 396 

Hesperopitheci, ii. 172 

Heterochronism, i. 13 

Heterotopism, i. 13 

Hind-brain, ii. 221, 232 

intestine, ii. 343 

limbs, ii. Ill 

Hip-bone, ii. 278 

His, Wilhelm, i. 64 

Histogeny, i. 24 

Histology, i. 24 

Histophyly, i. 24 

Hollow-worms, ii. 76 
Holoblastic eggs, i. 216 

Hologastrula, i. 241 

Homology of primitive intestin©, i 

247 ; ii. 321 
I of the animal tribee, iL 

387 
- germ-layers, i. 24t 

sexes, ii. 431 

Hood-gastrula, i. 200, 241 
Hoofed animals, ii. 160, 188 
Horn-plate, i. 307 
Horn-stratum of Epidermitf ii. 200 
Humerus, ii. 278, 304 
Huxley, i. 101 ; ii. 294 

germ -layer theory, i. 67 

— — — his Evidences, i. 101 
— — — Man and Ape, i. 101 

primates, law of, ii. 177 

skull theory, ii. 294 

Hylohates, ii. 181, 189 
Hypospadia, ii. 423 



Immacvlati conception, i. 170 
luiiMvhM ii. 159, 187 
Ixtdividaality, i. 123 



INDEX. 



497 



ladiTidaality of oells, i. 123 

of metamera, i. 348 

Indo. Germanic pedigree, ii. 23 
Induction, L 104 ; ii. 35 
Inorganic history of earth, ii. 5 
Insects, mental capacity of, ii. 4-^8 
Iniegume^Uxtm, ii. 199 
Intestinal germ-disc, i. 291 
• vesicle, i. 291 



head-caviiy, i. 336 

Intestine, after, ii. 321 

'■ blind, ii. 330 

crooked, ii. 319, 8S0 

dijjestive, ii. 330 

empty, ii. 330 

middle, ii. 330 

stomach, \L 330 

Inrertebrates, i. 414 
Iri», ii. 252, 258 



Jasgek, Qustav, i. 101 
Jaw arches, ii. 102 

lower, ii. 102 

upper, ii. 102 

JxiracBio period, ii. 14, 19 



Kaitt, Imm AircKL, i. 79 
KidnejB, ii. 403, 412 
Kidney system, ii. 403 

primitive, iL 306, 410 

Kenogenesis, i. 12 
Kftnogenetic cleavage, i. 231 
Kernel of oell (nncleus), i. 127 
Kleinenberg, Nioolaus, ii. 358 
KOUiker, Albert, i. 69, 62 
KowaloTsky, Aogost, L 59, 441 



Labtkiifth of kar, ii. 260 

Labyrinthulae, ii. 58 

Lamarck, Jean, i. 82 

his life, i. 82 

 Man and Ape, i. 85 

" ' " *' Philosophie Zoologiqne, 
i. 83 



» 



La/mina dermdUa i. 273, 327 

gastralis, i. 273, 327 

inodermalis, i. 327 

inojastralis, i. 327 

myxogastralis, i. 327 

neurodermalia, i, 827 

Lampreys, ii. 101, 121 
Lancelet, i. 253, 413 
Lankester, Ray, i. GO 
Lanugo, ii. 206 
Larynx, ii. 330 

Latebra (of bird's egg), i. 138 
Laurentian period, ii. 9, 19 
Layers (Lamince), i. 273, 327 
Leather.plate, i. 327 

skin, ii. 200, 232 

Leenwenhoek, i. 37 
Leg, lower, ii. 278 

upper, ii. 278 

Leibnitz, i. 39 
Lemuria, ii. 183 
Lemurs, ii. 164 
Lens, ii, 251, 254 
Lepidosiren parcuioxa, ii. 119 
Leptocardia, ii. 120 
Limbs, ii. Ill, 306 

fore, ii. 302 

hind, ii. 306 

skeleton of, ii. 305 

theory of, ii. 305 

Linnaeus, Karl, i. 7S 
Lip-cartilage, ii. 245 

fissure, ii. 246 

Liver, ii. 330, 341 
Lizards, iL 120, 129 
LocomotoriMmf ii. 194, 274 
Lori, ii. 163 
Lyell, Charles, i. 77 
Lymph-cells, ii. 366 
T«ss«ls, ii. 278 



Macula ftrmmativa, i. 133 
Magosphwra pUvnula,, iL 60 
Male breast, ii. 204 
cells, i. 171 ; ii. 392 

copulatory organs, ii. 42.'^ 

excretory ducts, ii. 414, A^ 

germ-glands, ii. 398 

germ-layer, ii. 898 



498 



INDEX. 



Male milk-glandB, ii. 204 

phallus (Penis), ii. 423 

sexual organs, ii. 431 

sexual plate, ii. 401 

uterus, ii. 419 

Malpighi, i. 31 

Malthus, i. 98 

Mamilla, ii. 204 

Mammaf Ii. 204 - 

Mammalia, ii. 141, 187 

Mammals, egg-cleavage of, i. 210 

gastrula of, i. 213 

—  mental capacities of, ii. 

448 
Man.4kpes, ii. 178 
Mantle animals, ii. 83 
Marsupobranchii, ii. 104 
Mwrsupialia, ii. 149, 187 
Martins, Charles, ii. 304 
Materialism, ii. 456 
Maternal placenta, ii. 160 
Matter, ii. 457 
Mechanism in nature, i. 80 
Meckel's cartilaa^e, ii. 298 
Medulla, ii. 211,^^232 

capitis, ii. 211 

centralis, ii. 211 

— oblongata, ii. 211 

— — — — spinalis, ii. 211 
MedoUary furrow, i. 302 

membranes, ii. 228 

plate, i. 327 

swellings, i. 308 

tube, i. 305 

Mmingea, ii. 228, 232 

Meroblastic eggs, 216 

Merogastrula, i. 241 

Mesentery, ii. 320 

Mesoderma, i. 236, 278 

Meaolithio epoch, ii. 14, 19 

Mesozoic periods, ii. 12, 14 

Meta,carj>us, ii. 278, 304 

Metagaster, ii. 321 

Metagastrula, i. 199 

Metameray i. 346 

Metamerio structure, i. 347 

Metanephra, ii. 412 

Metatargus, ii. 278, 304 

MetoMa (intestinal animals), i. 248 { 

n.92 
ldicrol4*t4»t ii. 149 
Mid.brain, ii. 221, 282 



Middle germ-layer, i. 278 

intestine, ii. 330 

layers, i. 278 

'■ part of foot, ii. 278, 304 

hand, ii. 278, 304 

Migration, theory of, i. 114 
Milk, ii. 202 

glands, ii. 143, 202 

Mind, ii. 226, 447 

activity of, ii. 210 

cells of, i. 129 

development of, ii. 450 

heredity of, ii. 452 

Molliisca, ii. 92, 94 
Monads, i. 39 
Monera, i. 180 ; ii. 43 
Monerula, i. 179 

Monistic philosophy, i. 16 ; ii, 466 
Monocondyles, ii. 138 
Monodelphia, ii. 151, 187 
Monogeny, i. 160 
Monophyletio origin, ii. 277 
MoTwrhina, ii. 101, 120 
Monotrema, ii. 145, 187 
Monstrons evolution, i. 168 
Morphogeny, i. 21, 24 
Morphology, i. 21 
Morphophyly, i. 24 
Morula, i. 189 
Motor apparatus, ii. 194, 274 

germinative layer, i. 330 

Mouth, i. 338; ii. 315, 830 

cavity, ii. 315, 330 

groove, i. 338 

Mud.fishes, ii. 115, 120 
Mulberry -germ, i. 189 
Miiller, Fritz, i. 59, 408 

Hermann, i. 170 

Johannes, i. 59 ; ii. 96, 414 

Miillerian duct, ii. 414, 431 
Muscles, i. 259 ; ii. 364 
Muscle-plate, i. 353 

system, ii. 308 

Mymvnoideg, ii. 101, 12Q 



N 



Nails, ii. 204, 232 

Natural history of creation, L lOt 

philosophy, i. 82 

Navel, i. 815. 335 



INDEX. 



499 



t^ATel arteries, i. 400 

cord, i. 384 ; ii. 168 

mesentery arteries, i. 395 

veins, i. 399 

reins, i. 399 

vesicle, i. 337, 377 



Neok curvature, i. 369 

marrow, ii 211, 222 

rertebrae, ii. 281 

Nerre-oells, i. 126 

system, ii. 211, 232 

Neuro-muscular cells, ii. 232, 236 
Nictitating membrane, ii. 259 
Nipples of milk-glands, ii. 202 
Nipple-less animals, ii. 146, 204 
Nose, i. 374; iL 247 

of Ape, ii. 175 

cavities, ii. 245 

flaps, ii. 243 

furrow, ii. 244 

grooves, ii. 244 

processes, ii. 242 

roofs, ii. 242 

Notaspis, i. 297 
Nucleohis, i. 133 
Nucleus^ i. 125 
Nutrition, i. 158 
Nutritive yelk, i. 216 



CKkoloot, L 114 
Oken, Lorenz, i. 49 
Olfactory grooves, ii. 240 

nerve, ii. 239 

organ, ii. 239 

Ontogenesis (evolution of the germ), 

i. 12 
Ontogenetic fission of the layers, 
i. 238 

unity, i. 366 

Ontogeny, L 6 
Oophora, ii. 898, 429 
Optic nerve, ii. 250 
Orang-outang, ii. 178, 181 
Orchides, ii. 399, 429 
Organic history of the earth, ii. 7 
Organisms without organs, ii. 46 
Organogeny, i. 24 
Organology, ii. 192 
Oiganophjly, i. S4 



Organ-Bygtemt, age of, ii. 357, 367 

human, ii. 194 

Original cleavage, i. 198, 241 
Ornithodelphia, ii. 145, 187 
Omithorhynchus, ii. 147 
Omithostoma, ii. 147, 187 
Os ilmm, ii. 278, 304 
Os ischii, ii. 278, 304 
Os pubis, ii. 278, 304 
Outer skin, ii. 200, 232 
Ovary, ii. 398, 430 

plate, ii. 401 

Oviduct, ii. 403, 429 
OvococcuSf i. 183 
Ovojtlasma, i. 183 
Ovtda holohlasta, i. 215, 241 

merohlasta, i. 216, 241 

Ovulists, i. 37 
Ovulvm, L 171, 183 



Pachycardia, i. 120 
Palate, ii. 330 

roof, ii. 330 

soft, ii. 330 

Palaeolithic epoch, ii. 10, 19 
Palaeontology, i. 106 
Palaeozic periods, u. 12, 13 
Palingenesis, i. 10 
Palingenetic cleavage, L 211 
Palingeny, i. 11 
Pcmcreas, ii. 330, 343 
Pander, Christian, i. 51 
Paradise, ii. 183 
Parallelism in evolution, ii. 70 
Parent-cell, i. 176 

kernel, i. 176 

Parov(vrivMty ii. 417, 4.31 
Parthenogenesi*, i. iO, 170 
Partial clearage, i. 316, 240 

of bird's egg, I 22 1 

Pastrana, Julia, i. 374 
Pedigree, i. 112 

of animals, ii. 98 

Apes, ii. 189 

cells, i. 467 

Indo- Germanic Ian. 

guages, ii. 23 
-^— — ^— Mammals, ii. 188 
— ^— — — mas, ii. 23 



500 



INDEX. 



Pedigree of Vertebrates, ii. 121 
Pelvic girdle, ii. 278, 304 

intestinal cavity, i. 335 

Prnvit, ii. 423, 431 
Pentadaetylia, ii. 123, 802 
Perigcutrula, i. 230, 241 
Peripheric nerve- system, ii. 228 
Permian period, ii. 10 
P»tromyM<mte$, ii. 101, 120 
PhallM, ii. 422, 431 
Phalhuia, i. 454 
Pharyna, ii. 316, 830 
Philology, ii 20 

comparative, ii. 21 

Philoiophy, i. 17 ; ii. 456 
Phylogene»i$ (evolution of the tribe), 
i. 12 

Phjlogenetio fission of the layers, 
i. 238 

hypotheses, i. 413 

Phylogeny, i. 5, 72 

Physiogeny, i. 21, 24 

Physiology, i. 20 

comparative, i. 20 

Physiophyly, L 24 

Pig, i. 362 

Pigment-membrane, ii. 252 

Pithecanthropi, ii. 181 

Pithecoid theory, ii. 441 

Placenta, i. 883 ; ii. 155, 168 

disc-shaped, ii. 162, 187 

©mbryonic, ii. 160 

fcetalis, ii. 160 

— — — — girdle-shaped, ii. 162, 187 

maternal, ii. 160 

uterina, ii. 160 

Placental animals, ii. 153, 187 

Placentalia, ii. 153, 187 

FUkfUM, ii. 61 

PbauMds, ii. 61 

Pbknt-animals, 

Planula, ii. 59 

Plasson, i. 130 ; ii. 43 

FlMtids, L 130 ; ii. 46 

Plastid ancestors, ii. 184 

FlMtid theory, i. 130 

Plastidoles, ii. 47 

Plates {lamella), i. 803 

PUOkehninthea, ii. 76 
PIntyrMno, ii. 175, 189 
Plonro-peritoneal cavity, L 26Q 
poriod, iL 11, 16 



Polydaetylia, ii. 123 
Poms genitalis, ii. 402 
Post-glacial period, ii. 11 
Pouch-bones, ii. 151 
Pouched animals, ii. 149, 187 
Praedelineation theory, i. 37 
PrBBformation, i. 34 

theory, i. 34 

Prmputium, ii. 423, 431 
Pressure, sense of, ii. 238 
Primary axial skeleton, iL 285 

age, ii. 10, 11 

germ -layers, i. 196 

Primates, ii. 169 

Primitive amnion animals, ii. 13t 

animal ancestors, ii. 184 

animals, or Protozoa, i. M# 

clavicula, ii. 278 

egg {Protovum), i. 134 

fins, ii. 303 

Fishes, ii. 112, 120 

furrow, i. 226 

germ-layers, i. 195 

groove, i. 335 

intestine, i. 444 ; ii. 318 

kidney, i. 306 ; ii. 410 

ducts, ii. 406 

Mammal, ii. 142, 187 , 

Man, ii. 182 

• mouth, i. 444 ; ii. 313 

skull, ii. 296 

slime, ii. 43 

streak, i. 299 

urine-bladder, ii. 411 

urine-sac, i. 379 ; ii. 41 1 

vertebrae, i. 346 

— '■ vertebral cords, i. 306 

vertebral plates, i. 346 

 — Vertebrate (ideal), L 256 

(real), iL 98 



Worm, ii. 74, 80 



Primordial cleavage, i. 198, 241 

kidneys, i. 307 ; ii. 410 

skull, ii. 297 

times, ii. 9, 11 

Prochorion, ii. 157 
Procoracoidevm,, ii. 278, 304 
Promammalia, ii. 142, 187 
ProsimicB, ii. 163, 187 
Protamosha, ii, 46 
Protamnionf ii. '83 
Prothelmitt ii. 76 



OTDEX. 



501 



FT<4oga$t€r, L 444 ; iL 314 
Frotorrvyza, ii. 46 
ProtoTiephra, ii. 410 
Protoplasma, i. 131 
Protopterua armecten*, ii. 119 
Protoioa, ii. 248 
Protureter, ii. 406 
Peeadopodia of Amoeb», i. 142 
Ptyche, ii. 225, 446 
Piychology, ii. 448 
Pttbio bone, ii. 278 
Pwnctum germinativumf L 186 
Pupil, ii. 252, 258 
'—— membrane, ii. 254 



SaeUiM, ii. 278, 304 

Rathke, Heinrich, i. 59 

Rathke's duct, ii. 415, 431 

Reason, ii. 453 

Reicbert, Bogulaus, i. 61 

Kemak, Robert, i. 62 

Re7ie$, ii. 412 

Reprodaction, i. 159 

Reproductive organs, ii. 392, 418 

Reptiles, ii. 120, 138 

Eespiratorj intestine, i. 262 ; ii. 330 

organs, i. 262 ; ii. 333 

Retina, ii 252, 258 
Bibs, ii. 285 
Rolle, Priedrich, i. 101 
Bound -month 8, ii. 101, 120 
Budimentary organs, i. 109 
Bmnp bone, ii. 282 

vertebrae, ii. 282 

SuBCOni, anus of, i. 206 
BwKKmi'a nutritive oavitj, L 907 



Salamakdei, ii. 127 
Salivary glands, 
Bwuropsida, ii. 138 
Scapula, ii. 278, 303 
Schleidon, M. J., i. 60, 128 
8<diwaim, Theodor, i, 60 
aeUrvtiem, i Ul, 268 



Seoleeidoi ii 88 
Scrotum, ii. 423, 431 
Sea-Lettlea, ii. 73, 92 
Secondary age, ii. 11, 14 

axial skeleton, ii 291 

germ -layers, i 235, 3fTh 

kidneys, ii. 412 

; sexual chanicter, ii. 3i^ 

— strata of earth, ii. 12 



Seed (male), i. 36 

animalcules, i. 173 

cells, i. 173 

duct, ii. 403, 429 

Segmental canals, ii 406 
Segmentation, i. 186 
Segmentella, i. 186 
Selachii, ii 112, 121 
Selection, theory of, i 96 
Semi-apes, ii. 164, 187 
Semicircular canals -of ear, ii. 26r? 

268 
Semper, Karl, i 91, 426 
Sense oiP pressure, ii. 238 

of warmth, ii. 238 

Sense-organs, ii. 238 
Sensorium, ii. 194 
Sensory a]'paratus, ii. 194 

functions, ii. 238 

layer, i. 236, 229 

nerves, ii. 238 

Sexes, separation of, ii. 69, 896 
Sexual cells, origin of, 

cord, ii. 418 

ducts, ii. 402, 429 

folds, ii. 422, 431 

furrow, ii. 422 431 

glands, ii. 398 

 nerves, ii. 238 

organs, i 266 

plates, ii. 399 

selection, i 103 ; ii. 894 

sense, ii. 238 

Sheath {Va<fina), ii. 417, 481 

of amnion, i 387 

Shin-bone, ii. 278, 304 
Shoulder-blade, ii. 278, 804 

 girdle, ii. 278, 304 

Side-layers, i. 303 

plates, i. 303 

sheath, i. 308 

Silurian period, ii. 9, 19 
Shuniatt ii. 165 



50J 



INDEX. 



Sing^*-noetnl8, ii. 101, 120 
SmtLS urogenitalis, ii. 419, 421 
Siredon, ii. 129 
Skeleton, ii. 278 

Skeleton-forming cell-layer, ii. 287 
Skeleton, muscles of, ii. 194 

plate, ii. 287 

Skin, ii. 195, 229 

corering, ii. 195, 232 

fibrous layer, i. 236 

■- — glands, ii. 201, 232 

layer, i. 236 

muscle layer, i. 236 

moBcles, ii. 194 

— .— narel, i. 317 

iMrres, ii 238 

sensory layer, i. 236 

stratum, i. 236 

SkHll, ii. 292 

floor, ii. 292 

roof, ii. 292 

vertebrae, ii. 294 

theory of, iL 295 * 

Skulled Animals, ii. 100 
Skull-less Animals, i. 416 ; ii. 99 
Small brain, ii. 213, 232 
Soft-bodied Animals, ii. 92, 94 
Soft worms (Scolecida), ii. 86 
Sozohranchia, ii. 129 
Sozura, ii. 129 
Species (idea of), i. 73, 116 
Sperma, i. 171 
8permaduetu$, ii. 403, 429 
Spermalists, i. 37 
Spermatasoa, i. 172 
Sp^rm-cells, i. 172 
Sperm^coccxis, i. 7 S3 
3p«rmopla*ma, i. 188 
3p«rmviwnf L 183 
Spine, ii. 280 
SpiritualijBii, ii. 456 
Spoke-bone (Radiiut), ii. 278, 304 
Sponges, ii. 73, 92 
Spontaneous generation, ii. 80 
Star.animals, i. 435 
Stenops, iL 164 
SUrnun^ ii. 278 
Stomach, ii. 330 

intestine, ii. 830 

8trT!ggle for existence, i. 96 
S^theuHs, iL 232 

ii*7V 



Superficial clerwage, i. 229 
Sweat-glands, ii. 202 
Swimming-bladder, ii. Ill, 336 
Sylvian aqueduct, ii. 221 
Synairuebinm, ii. 56 
System of animals, ii. 92 
germ-layerH, i. 273, 327 

mammals, ii. 188 

organs, ii. 194 

tissues, ii. 366 

vertebrates, ii. 120 



Tadpolks, ii. 128 

Tail, human, i. 372 ; iL 28S 

Tail-cap, i. 387 

curvature, L 369 

sheath, i. 387 

vertebrae, ii. 283 

Tailed apes, ii. 180 

Batrachia, ii. 129 

Tarsus, ii. 278 

Taste, nerve of, ii. 238 
— sense of, ii. 238 
Teeth, ii. 173, 331 
Tegumentum, ii. 199 
Teleology, i. 16, 109 
Teleostei, ii. 115, 120 
Terminal budding, i. 349 
Tertiary age, ii. 11, 15 
Testes, ii. 399, 429 
— — ^^ change of place of, iL 419 

sac, ii. 423, 431 

TesticuU, ii. 399, 429 
Theoria Oenerationis, L 41 
Thorax, ii. 282 
Thyroid gland, ii. 336 
Tibia, ii. 278, 304 
Tissues, ii. 362, 366 

age of, ii. 361, 366 

connective, ii. 363 

— — — covering, ii. 361, 368 

vascular, ii. 361, 366 

Total cleavage, i. 217, 242 
Tongue, ii. 331 

arch, ii. 296 

bone, ii. 298 

Tortoise, ii. 120 
ToMk bodies, ii. 220 



INDEX. 



S03 



Toneh, organ of, ii. 199, 238 
Transition forms, i. 117 
Tread, i. 138 
Triasaio period, ii. 14, 19 
Tribal history, i. 7, 24 
Trophic germ-la jer, i. 239 
TubcB FalUypicB, iL 431 
Tube-hearta, ii. 120 
TvinietUa, ii. 83, 92 
Twhellaria, ii. 79 
Twixt-brain, ii. 220, 282 

jaw, ii. 246 

Tjmpasie oarity, ii. 261, 268 

membrane, ii. 261, 2fJ8 

Tympanum, ii. 261, 268 
Types in animal kingdom, i. 56, 246 
of , L 66, 246 



Ulna, ii. 278, 304 

UnguUita, ii. 160, 188 

CTnitary conception of the world, i. 

17 ; ii. 456 
Urachus, ii. 413 
Ureter, ii. 413 
Urethra, ii. 423, 431 
Urinary bladder, ii. 418 

ducts, ii. 406 

organs, ii. 403 

sac, i. 379 

sexnal cavity, ii. 419 

sexnal duct, ii. 403 

system, ii. 403 

Ulenis, ii. 417, 431 

bicornis, ii. 418 ' 

masculirvus, ii. 419 

{Timlo, ii. 430 



Vchgina, ii. 417, 481 

Vamjyyrella, ii. 48 

Van Beneden, Eduard, i. 60, 209; 

ii. 398 
7m« deferentia, ii. 403, 429 

wnbiUcalia i. 399 

Vawrnlar syitem, ii. 384 



Vegetatire germ-layer, i, 196, 327 

organs, ii. 193, 194 

Veins, i. 393 
Ventral cavity, i. 316 

plates, i. 316 

vessel, i. 423 

— wall, i. 316 

Ventricle of heart, ii. 374 

Vermal appendage of coeoum, ii. 34 

Vertebraa, ii. 280 

number of, ii. 288 

Vertebral arches, ii. 284 

bodies, ii. 284 

canal, ii. 284 

column, ii. 280 

Vertehrarium, ii. 278 

Vertebrat-es, ii. 92 

Vertebrates, ancestoni o^ ii. 186 

mental capacities o! 

ii. 446 

pedigree of, ii. 93 

system of, ii. 97 

Vesicula hlastodermica, i. 290 

germinativa, i. 133 

prostatica, n. 419 

umhilicalii, i. 377 

VesUhulum vagirux, ii. 431 
Virginal generation, i. 170 
Vitellus, i. 135 



Wagwer, Moritz, i. 114 
Wallace, Alfred, i. 98, 99 
Water, amount of in body, ii. 7 
Whale.like Animals, ii. 160, 189 
Whales, ii. 160 
Wolff, Caspar Friedrioh, I 40 

his life, i. 41 

his Natural Philosophy, i. 47 

on formation of intestine, i. 44 

on germ-layers, i. 45 

Theoria QeneratiorUg, L 41 

Wolffian bodies, ii. 411 

duct, ii. 414, 431 

Wolff's primitive kidneys, ii. 411, 4;'« ' 
Woolly hair of embryo, ii. 206 
Worms, i. 246 ; ii. 74 

ancestors of, ii. 78 



- tribe of, ii. 73 



Wrist, ii. 278 



^04 



iKDBt. 



Vklk, i. ISft 

arteries, L 396 

cavity, i. 138 

duct, i. 388; ii. 168 

fonnativa, i. 216 

membrane, i. 138 

— mxtritire, i. 216 
— no, L 887 



T«lk T«ma, L 895 

TeseelB, i, 396 



Zona pMueida, i. 135 
ZofUiplaeentaUa, iL 162, 187 
Zcophyta, i. 2^ ; iL 78 



(15) 



THE END. 



