THE OCELLI OF ARCTIID MOTHS - ULTRASTRUCTURE OF THE RETINA DURING LIGHT AND DARK-ADAPTATION

The ultrastructure of the dorsal ocelli of two arctiid moths (Arctia c aja (A, caja) and Creatonotos transiens (C. transiens) was investigate d, The two ocelli are positioned laterally on the vertex of the head p osterior to the antennae, close to the dorsal margin of the compound e yes, The biconvex corneal lens is located at the apex of a cone-shaped cuticular elevation, which encapsulates the retina, The corneagenous cell layer and the cup-like retina with about 100-130 receptor cells i n A, caja (70-90 receptor cells in C. transiens) are adjoined proximal ly, The retina is completely enclosed by the perineurium and thus sepa rated from the corneagenous cells and the surrounding hemolymph, Irreg ularly shaped rhabdomeres, consisting of densely packed microvilli, ar e present in the distal region of the receptor cells, Up to three cell s may form a rhabdom, Thus a loose network of photoreceptive structure s over the whole retina results, A unique feature of these arctiid oce lli are photoreceptor vacuoles containing microvilli, The function of these organelles is unknown, The rhabdomeric arrangement within the li ght and dark adapted retina differs considerably. The ultra-structure of the rhabdomeres indicates an intense membrane turnover, However, ch anges in adaptation state are not accompanied by dramatic changes in t he photoreceptive area of an ocellus.