Spermatogonia and the cycle of the seminiferous epithelium in the nine-banded armadillo.

The cycle of the seminiferous epithelium of the nine-banded armadillo can be divided into ten stages. As in most mammals, only one stage is observed per tubular cross-section. The process of spermiogenesis can be divided into thirteen steps according to the development of the acrosomal system and the flagellum. Four generations of spermatogonia are abserved in the germinal epithelium: 1) stem cells, 2)type "A", 3) intermediate, and 4) type "B" spermatogonia. The stem cell is characterized by a highly irregular nucleus and the presence of glycogen in its cytoplasm. The type "A" spermatogonium contains an oblong nucleus with one or two shallow infoldings of the nuclear membrane. The intermediate spermatogonium contins an ovoid nucleus characterized by one or two nuclei and heterochromatin scattered in the nuceoplasm. The nucleus of the type "B" spermatogonium is more spherically shaped with a centrally placed nucleolus and heterochromatin associated with the nuclear envelope.