The Ultrastructure of the Photosensible Elements in the Eyes of Collembola and Their Orientation (Insecta)

Abstract

Collembola maximally have eight ommatidia on each side of the head, forming a so-called “atypical complex eye”. Their constructions are remarkably different within the order. In respect to their symmetries the rhabdoms of the known species can be distinguished in (1) completely irregular rhabdoms (Orchesella), (2) radial symmetrical rhabdoms (Tomocerus, Sminthurides), (3) bilateral symmetrical rhabdoms (Podura, Neanura, Entomobrya, Allacma (Sminthurus). All rhabdoms consist of eight retinula cells (except in Sminthurides) which form a photosensible part in a very different manner. In Orchesella, Allacma and Entomobrya you may find eight, in Tomocerus seven, in Podura four or six (double eye!), and in Neanura six rhabdomeres. In the compound eye of Podura all rhabdoms considered as cross-sections (fig. 3) lie parallel to one another (disregarding the curvature of the complex). In that of Entomobrya they lie in distinct angles of 30°, 60°, 90°, and 120° to one another (fig. 4).