Three types of the A-neurosecretory cells (NSCs) were found in the pars intercerebralis (PI) of the adult brain of four species of tsetse flies (Glossina palpalis, G. pallidipes, G. austeni and G. morsitans). The typical formula of their composition is: 8 A1-, 14 A2- and 4 A3-cells. After permanganate oxidation, the neurosecretory materials (NSMs) of Al- and A3-cells are rich in strong acid groups. The A2-NSM contains both strong and weak acid groups after this treatment; besides, it retains a weak affinity to acid dyes. In addition to the A-cells, the PI of Glossina species seems to include a number of NSCs of the type B.
The data obtained indicate a great similarity of the NSC composition in the PI of Glossina and other related higher dipterans.
In addition to the NSCs, giant neurons and particular cells with large cytoplasmic inclusions were also found in the PI of Glossina. The cells with large cytoplasmic inclusions correspond apparently to vacuolated cells previously observed in the brain of some flies. It is suggested that the considerable complication in reproductive biology which took place in tsetse flies had no effect on the composition of the NSCs in their PI when compared to that in related species with more ordinary cycles of reproduction.