STRUCTURE OF THE TESTIS FOLLICLE IN RELATION TO EVOLUTION IN THE SCARABAEIDAE (COLEOPTERA)

Abstract

In the coleopterous family Scarabaeidae the external morphology of the testis follicle varies much between different species. Three form groups can be distinguished. In one group, containing representatives of the systematically low coprophagous scarabs, differences are chiefly in the length of the follicle. In another group, typical representatives of which are the aphodines, the follicles are always spherical, but the size varies between different species. In the third, the follicles differ also in relative breadth. The third group contains higher phytophagous scarabs. The author suggests that the follicles of group 1 are the most primitive, those of group 3 the most advanced in the Scarabaeidae. A tendency to shorten, round out, and, finally, broaden the follicle seems to characterize the process of differentiation of the higher scarabaeoids from the primitive ones. This differentiation is accompanied by development of certain histological features in the follicles. In coprophagous scarabs the follicles are non-septate, the oxygen supply deriving directly from the central network of tracheoles. In phytophagous scarabs, oxygen and certain other nourishing stuffs are conducted by the septum system, which develops by invagination of the surface membrane of the follicle.