Spermatogenesis in the grasscutter, Thryonomis swinderianus (Rodentia).

Spermatogenesis in the grasscutter, Thryonomis swinderianus, is characterized by remarkable diversification of the endoplasmic reticulum. In spermatocytes, besides the usual form with flat cisternae and vesicles, this membrane system forms unusually wide cisternae and vacuoles containing moderately electron dense material near the Golgi apparatus and the cell membrane. In spermatids a whorl of smooth cisternae enclosing aggregates of granular electron dense material appears as another specialization. Although all parts of the endoplasmic reticulum are in connection with each other, their distinct structural differences suggest functionally different subcompartments. Once established, the structures persist even after cytoplasm has been discarded from the nearly mature sperm. In the elongating spermatid a thin plica of the Sertoli cell begins to separate the developing structures from the remainder of the cytoplasm containing the endomembrane systems, part of which is further ensheathed when this fold enroles to form an incomplete tube. Occasionally, in late spermatids a spindle-shaped body of paracrystalline structure occurs temporarily around the flagellum at the beginning of the main piece.