[Development of male germ cells in the fur seal (Callorhinus ursinus)]

Three types of spermatogonia have been distinguished in the fur seal: type A, intermediate, type B. The type A spermatogonia are presented by means of five varieties: stem A, A1, A2, A3, A4. The spermatogonia of the stem A type is characterized with presence of equally distributed chromatin in the nucleus. The spermatogonia of the A1-A4 types are characterized with a gradual condensation of chromatin. The intermediate spermatogonia possesses a light nucleus, chromatin as small and large granules is situated near the nuclear membrane. The spermatogonia of B1-B3 types have a round nucleus, their chromatin is granular. Spermatocytes both at the leptotene stage and at the zygotene stage are presented by means of three cellular forms. At the pachytene stage four cellular forms are distinguished. Basing on formation of the acrosomic apparatus, 18 stages of spermatids development are distinguished.