Definition of the stages of the cycle of the seminiferous epithelium of the opossum (Didelphis azarae, Temminck, 1825).

Spermatogenesis of the opossum (Didelphis azarae, Temminck, 1825) as revealed by the ferric hematoxylin technique is described. The spermiogenesis is subdivided in 15 steps characterized by changes observed in the nucleus and in the acrosomic structure of the spermatids. Using the morphological changes during the spermatids' maturation, a classification into 10 stages is proposed for the various cellular associations during the cycle of the seminiferous epithelium of the opossum.