Spermatogenesis in the Watase's shrew, Crocidura watasei--a light electron microscopic study

Spermatogenesis in the Watase's shrew, Crocidura watasei, was investigated by light and transmission electron microscopy. The cycle of the seminiferous epithelium was divided into 12 stages using the development of spermatids as a main criterion. The steps of spermatids were characterized by morphological changes of the nucleus and acrosomal structure. The relative frequencies of the stages 1 to x 11 were 11.0, 10.3, 6.8, 10.6, 24.0, 6.4, 4.4, 7.9, 6.4, 4.9, 3.7 and 3.6%, respectively. Four types of spermatogonia (A1, A2, In and B) could be discerned by the observation of whole mount samples. The development of spermatids was divided into four phases (Golgi, cap, acrosome and maturation phases), as in other mammals. In Golgi phase of the spermatid, several acrosomal granules were encountered. In cap phase, the acrosome gradually spread over the nuclear surface. In early acrosome phase, the acrosome began to elongate and reached the maximal length in step 8 spermatids. The acrosome of step 8 spermatids was twice as long as that of spermatozoa. In late acrosome phase, the acrosome was on the way of shrinkage. Finally, the fan-shaped acrosome was formed in maturation phase. These findings suggested that the process of acrosomal formation was quite characteristic in the Watase's shrew in that the spermatid acrosome elongated most prominently in the mammals hitherto examined.