COMPOUND EYE ULTRASTRUCTURES IN 6 SPECIES OF ECOLOGICALLY DIVERSE STAG-BEETLES (COLEOPTERA, SCARABAEOIDEA, LUCANIDAE)

The structural organizations of the compound eyes of six Japanese stag -beetles, i.e. Aesalus asiaticus (abbr. Aa) and Platycerus acuticollis (Pa) of the subfamily Aesalinae, Figulus boninensis (Fb) of the Figul inae, Nipponodorcus rubrofemoratus (Nr) of the Dorcinae, Lucanus macul ifemoratus (Lm) and L. gamunus (Lg), both of Lucanidae, were examined by light and electron microscopy. The results of this study formed the basis for a comparison between eye structures on the one hand and bee tle ecology, activity, and phylogeny on the other. In Pa, instead of a true cone, some electron dense material was seen in each cone cell; t his suggests that the typical ''eucone condition'' had been replaced b y an acone type of eye or a transitional condition between the eucone and acone types. The eyes of all other species were of the eucone type . The retinae of both Aa and Pa exhibited typically photopic organizat ion, but those of Nr and Lm were clearly representatives of the scotop ic type. The retinae of Fb and Lg were intermediate in nature. The ret inula cells numbered eight in Aa, Pa, and most of the ommatidia of Fb; in the other species they varied in number from eight to 11. Conseque ntly, the rhabdom itself exhibited variations depending on the number of the retinula cells. With 88%, the ratio of rhabdom to cytoplasmic a rea in transverse sections of the retinula cells, was largest in Lm an d Nr, while in Aa and Pa it measured a mere 5-6%. The differences appe ar to parallel the degree to which the species are active in day or at night.