STRUCTURE OF THE TESTES, SPERMATOZOA AND SPERMATOZEUGMATA OF MIMAGONIATES-BARBERI REGAN, 1907 (TELEOSTEI, CHARACIDAE), AND INTERNALLY FERTILIZING, OVIPAROUS FISH

The testis of Mimagoniates barberi is bipartite. Spermatogenic tissue is restricted to the anterior part. The posterior part of the testis i s devoid of spermatogenic tissue and contains numerous efferent ducts filled with mature sperm. Cells in germinal cysts develop synchronousl y, sperm nuclei and flagella become oriented parallel in the late stag es of spermiogenesis. In the caudal portion of the aspermatogenic part all sperms are arranged into unencapsulated sperm bundles -spermatoze ugmata. Two types of spermatozeugmata are found both in the caudal por tion of the testis and in milt. In the larger, spindle-shaped type, sp erm flagella form the spindle tips. In the smaller ones, which have ap proximately a length of spermatozoon, the sperm are parallel and appro ximately in register. In both types sperm heads are arranged parallel. A mature spermatozoon is flail-shaped. The sperm head is highly elong ated and situated alongside the flagellum, the tip of the head is dire cted backwards. Large mitochondria are situated on one side of the elo ngated nucleus only and form the tip of the head. Live spermatozoa mov e with the centriolar part ahead. Both testis and spermatozoon structu re as well as formation of spermatozeugmata in M. barberi are highly d erived features which perhaps evolved as adaptations to internal ferti lization.