The eye of Dytiscus (Coleoptera)

Abstract

The eye of Dytiscus (Coleoptera) has rhabdomeres at three different levels. The crystalline threads stretch from the ends of the crystalline cones only as far as the distal layer of rhabdomeres. There is one distal rhabdo-mere per ommatidium, and in this system the ommatidia are anatomically separate. Between the distal rhabdomere and the rhabdomeres of the next six retinula cells is a wide clear zone in which light entering by one facet could possibly reach deep rhabdomeres of a different ommatidium. Of the six proximal rhabdomeres, four have rhabdomere tubules which lie horizontal with reference to the normal posture, the other two having vertically oriented tubules. The eighth cell, with nucleus near the basement membrane, has a small rhabdomere. All eight retinula cells have axons and there is no other class of axons in the eye.