ULTRASTRUCTURAL-STUDY OF THE EUPYRENE SPERMATOZOON IN AMPULLARIA-CANALICULATA (GASTROPODA, PROSOBRANCHIA)

The fine structure of eupyrene spermatozoon, a terminal element of the typical spermatogenetic line, has been studied with electron microsco py. The cytodifferentiation process starts in isogenic groups of round ed spermatids. At nuclear level this process implies morphological cha nges and a progressive condensation of chromatin which forms an elonga ted nucleus, helicoidally folded and greatly electrondense. In the spe rmatic cytoplasm, the Golgi complex participates in acrosome formation . Flagellum is organized in a 2 + 9 microtubular pattern. This axoneme appears surrounded by mitochondria at the midpiece and glycogen granu les at the principal piece. A manchette surrounds the nucleus and the medium flagellar piece. Towards the end of eupyrene spermiogenesis, th e manchette is disorganized, the exceeding cytoplasm is eliminated and the gamete acquires its final morphology in relation to its reproduct ive function.