The cycle of the seminiferous epithelium in the greater Japanese shrew mole, Urotrichus talpoides

Spermatogenesis and acrosomal formation in the greater Japanese shrew mole, Urotrichus talpoides, were studied by light microscopy. On the basis of ac rosomal changes, morphology of spermatid head, nuclear shape, appearance of meiotic figures, location of spermatid and period of spermiation, the cycl e of the seminiferous epithelium was classified into 12 stages, and develop ing spermatids could be divided into 15 steps. The mean relative frequencie s of stages from I to XII were 10.9, 8.7, 9.8, 7.3, 8.5, 10.3, 12.5, 8.7, 5 .8, 5.4, 5.1 and 7.1%, respectively. Similar to the case in the musk shrew, the spermatid nucleus of the greater Japanese shrew mole remained in the m iddle region of the seminiferous epithelium and only the acrosome extended towards the basement membrane. The elongation of the acrosome, however, was not prominent. The proacrosomal vesicle first appeared in stage II and the n one large and round granule was seen in stage III. The acrosomal vesicle became flattened on the surface of the nucleus in stage IV. Spreading of th e acrosomic system has been recognized from stage VII. In stage VII, spermi ation occurred. In stage IX, the spermatid nucleus began to elongate. Elong ation and condensation of the nucleus were clearly observed in stage X. In stage XII pachytene spermatocytes divided into diplotene spermatocytes. In stage XII, meiotic figures and secondary spermatocytes were observed.