Figure 20. Arrangement of receptors in the tiered retina of the AME. 1, Anterior view of an adult female Colonus sylvanus (Hentz 1846), depicting the boomerang shape of the AME retinae (in green), and the alignment of respective fields of vision (outlined in yellow). White arrows depict the six directions in which each AME can be moved, to include left-right, up-down, and clockwise-counterclockwise rotation. Each of these directions corresponds to the contraction of a set of oculomotor muscles that position the long AME eye tube within the prosoma. After Hill 2018a. 2, Parasagittal diagram of the respective alignment of receptors in the four layers of the AME of Servaea vestita, near the center of the retina. The identity of the receptors shown in orange was not known. Red rectangles show the position of columns connecting layers I and 2. After Blest et al. 1981. 3-6, Diagrams of serial (proximal to distal) transverse sections through the retina of S. vestita, showing a cross section of individual receptors by layer (after Blest et al. 1981; Blest 1988). Lateral receptors of layers III-IV include groups 3a, 4a and 4c. Medial receptors of these layers include group 3b and 4b. Based on the findings of Nagata, Arikawa & Kinoshita (2019; see Figure 22:5), the separation of layer III and IV receptors into these lateral and medial groups may have more anatomic or functional significance than their relative position (or layer) along the axis of the eye.