RETINAL ULTRASTRUCTURE OF THE DORSAL EYE REGION OF PARARGE AEGERIA (LINNE) (LEPIDOPTERA, SATYRIDAE)

We examined the fine structure of dorsal rim ommatidia of the compound eye of Pararge aegeria (Lepidoptera: Satyridae) and compared them wit h ommatidia of the large dorsal region described by Riesenberg (1983 D iploma, University of Munich). 1. The ommatidia of the dorsal rim show morphological specializations known to be typical of the perception o f polarized light: (a) the dumb-bell-shaped rhabdoms contain linearly aligned rhabdomeres with only 2 orthogonally arranged microvilli orien tations. The rhabdoms are composed of the rhabdomeres of 9 receptor ce lls, 8 of which are radially arranged. The rhabdomeres of receptor cel ls V1 and V5, as well as D2, D4, D6 and D8 are dorsoventrally aligned, whereas the rhabdomeres of the cells H3 and H7 are perpendicular to t hem. The rhabdomere of the bilobed 9th retinula cell lies basally and is dorsoventrally aligned, where retinula cell V1 and V5 are already a xonal. (b) There is no rhabdomeric twist, and (c) the rhabdoms are rat her short. 2. However, in the ommatidia of the large dorsal region, on ly 2 retinula cells (H3 and H7) are suitable for perception of polariz ed light. 3. Lucifer yellow and horse radish peroxidase were used as t racers to visualize the projections of retinula cell axons of the dors al rim area and the large dorsal region into the optic neuropils (lami na and medulla). Two receptors (V1 and V5) from both the dorsal rim ar ea and the large dorsal region, have long visual fibres projecting int o the medulla. The 7 remaining retinula cells of both eye regions, inc luding those that meet the structural requirements for detection of po larized light in the large dorsal region, terminate in the lamina (sho rt visual fibres). These results provide a starting point for further studies to reveal the possible neuronal pathways by which polarized li ght may be processed. Copyright (C) 1996 Elsevier Science Ltd.