The irregular-shaped spermatogonia form a peripheral layer, and show a prominent nucleus. Spermatocytes are larger than spermatogonia, and in the early stage present synaptonemal complex.
Spermatids show nuclei smaller than the spermatocytes.
Spermiogenesis is characterized by outgrowth of the zone of differentiation, presenting basal bodies, separated by an intercentriolar body. At the end of this process, the spermatozoa are released into the residual cytoplasmic mass. The peripheral cortical microtubules on the dorsal and ventral faces are laterally interrupted. The present study describes the ultrastructure of spermatogenesis and the fine structure of the mature spermatozoon in a digenean species, Sacco-coelioides godoyi , parasite of the freshwater fish, Leporinus friderici . To the Superintend ncia do Meio Ambiente Aqu tico, Centro de Pesquisas and Dr Carla Canzi from Itaipu Binacional, for the facilities offered to examine the fish from the Paran River.