THE COMPOUND EYE OF THE DUNG BEETLE, BOLBOCEROSOMA-NIGROPLAGIATUM (COLEOPTERA, SCARABAEIDAE)

The compound eye of a nocturnal dung beetle, Bolbocerosoma nigroplagia tum, was observed by light and electron microscopy and compared with t hat of other scarabaeid beetles. The eye is completely divided into tw o parts by a well developed canthus into relatively narrow dorsal and comparatively wide ventral eyes. The inner surface of the cornea protr udes inwards and forms an exocone, while at the same time the crystall ine cone is much reduced Such a condition of a ''duocone'' dioptric ap paratus seems to have been found so far only in Omorgus of the Trogida e. The retina is of the scotopic type, and the configuration of the rh abdom is different in dorsal and ventral eyes. The rhabdoms of several rows of the dorsalmost region in the dorsal eye are composed of three rhabdomeres in which parallel and long microvilli are orientated in t hree directions, and four V-shaped rhabdomeres in transverse section. In the remaining part of the dorsal eye as well as in the entire ventr al eye, the rhabdoms exhibit a seven-lobed pattern. One of the rhabdom eres is formed by parallel and linear microvilli which are less electr on-dense. A microvillar arrangement such as this suggests a special fu nction e.g. polarization vision.