Cobalt staining techniques were used to compare the amounts and sizes of ocellar L-neurons of the American cockroach Periplaneta americana at various stages of development. Molting was observed; the head width, brain size, and ocellar corneal diameter were measured to investigate their relationship to body growth. The results show that after the sixth instar (body length 12-15 mrn), the head width, brain width, and ocellar morphological changes are progressively related to body length. Individuals of body length shorter than 12 mm have no ocellar cornea. The ocellar cornea diameter in adults was double that of nymph instars. The results also showed that except for those individuals of less than 10 mm in body length, each ocellus contains three or four L-neurons at various stages. Their cell bodies are oval, and the diameter increases as the individual grows, about 10 µm in early stages and 30 µm in the adult stage. The cell bodies are distributed irregularly in the forebrain near the protocerebral bridge, some are strung together and some are dispersed.
Periplaneta americana, Ocellar L-neurons, Cobalt staining method
