Spermiogenesis And the Cycle of The Seminiferous Epithelium in The Platypus, Ornithorhynchus Anatinus.

Abstract

Department of Biological Sciences, University of Newcastle, New South Wales 2308. Ultrastructural studies of spermiogenesis in platypuses indicate that they display some unique features. The origin and morphology of the perforatorium are different than in sperm from birds and therian mammals, and development of the fibrous sheath of the principal piece starts much later in the platypus. However, some features of spermiogenesis in the platypus are similar to birds, but different from therian mammals. For example, the dense granules in the developing acrosome of therian mammals are absent in platypus spermatids. Other features of spermiogenesis in the platypus are similar to processes described in therian mammals, but not birds. For example, the acrosome of platypus sperm is not confined to the rostral surface of the nucleus as in avian sperm, but extends laterally over the nucleus as in sperm from therian mammals. Further, during spermiation the tubulobulbar complexes were also observed in the platypus. Sixteen steps of spermatid development were identified and used to classify the cycle of the seminiferous epithelium into 12 stages. The area of the wall of a seminiferous tubule, which is occupied by a stage of the cycle of the seminiferous epithelium in the platypus (about 6-8 stages of the cycle per tubular cross-section), is between that of therian mammals (1-4 stages) and birds (up to 12 stages). The cycle ofseminiferous epithelium will provide a basis to determine the rate of sperm production in the platypus.