Histological changes in the brain of Hypsa alciforon (Lepidoptera:Hypsidae) during metamorphosis.

The histology of the larval and adult brain and changes in the former during pupal period is described. The bilobed larval brain consists of the three neuromeres- proto-, deuto-, and tritocerebrum. The protocerebrum has corpora pedunculata, ponscerebralis, parsintercerebralis, central body, corpora ventralia and three optic lobe anlagen. The lamina and medulla interna are joined with their counterparts of the opposite sides by anterior and posterior optic commissures respectively. Deuto- and tritocerebrum are not well marked. The cortex of the brain consists of four types of glial cells, association neurons and large and medium sized motor neurons. Besides an increase in the size of the larval brain certain new structures differentiate from the larval centres. These are ellipsoid body, three optic ganglia, differentiation of the deutocerebrum into an outer nodular and inner fibrous region. Degeneration and reformation of the neural lamella is also observed during pupal period. Fibrous chiasm between the optic centres are also formed in this period. A pair of small rounded ventral tubercles get differentiated. The medulla interna of the larva divides into a "lobula" and "lobula plate". A fibrous connection is established between the stalks of the opposite sides. The optic centres of opposite sides get connected with each other by three optic commissures. The three neuromeres become externally visible and with these changes the larval brain gets converted into the adults.