Sertoli cell-spermatid tubulobulbar complexes in the ram.

The fine structure of the tubulobulbar complex (TBC) of the ram seminiferous epithelium was studied in immersion-fixed testicular samples obtained in autumn (sheep's mating period). The TBC was visible during the last two stages of the seminiferous epithelium cycle. It originated as a tubular invagination of the Sertoli cytoplasm harbouring a complementary evagination for the spermatid head. Later, it expanded into a bulbous structure, finally becoming detached from the spermatid and apparently phagocytosed by the Sertoli cell. The significance of this transient structure is discussed and compared with previous reports for other eutherian mammals.