Distribution and structure of ocelli in Lepidoptera previously reported to be anocellate and morphology of a nerve complex associated with the ocelli

Abstract

The distribution of internal ocelli has been extended to include not only additional anocellate moths but also two species of butterflies. The possible presence of internal ocelli of a different external structure in other Ropalocera is also examined.

The structure of internal ocelli is examined by light and electron microscopy. A unique circular rhabdom apparently composed of a single retinular cell was observed in the internal ocelli of sphingids. Pigment cells were found to be absent. Observations were also made on the synapse between first and second order neurons where an apparent axosomatic synapse was found.

A nerve complex was found to be associated with the internal ocelli of moths. Nerve branches were found to connect the ocelli to the antenna! nerve, optic lobe, corpus cardiacum and sometimes the tegumentary nerve as well as the external ocellus.

Adult moths and butterflies reported to lack external ocelli were found to possess a pair of small external ocelli located on the vertex posterior to the antennae and dorso-medial to the compound eyes. Scanning electron microscopy and histological studies showed the external ocellus to consist of a corneal lens about 26 µ in diameter with cells beneath it. A nerve branch was found to extend from these cells to the internal ocellus in moths. Thus the possibility of a two-part ocellus exists.