The spermatogenic cycle in the silver fox (Vulpes vulpes): frequency of the different stages prior to and during the breeding season.

In the silver fox the cycle of the seminiferous epithelium could be classified into eight characteristic stages defined on the basis of different, well-defined cell associations. The main criteria for the staging were the type of spermatogonia, the appearance of primary spermatocytes, the occurrence of meiotic figures and secondary spermatocytes and the shape and location of spermatids. In some cases more than one stage could be found within the same transverse tubular section. The average frequency of stages I to VIII was 25.2, 8.2, 9.0, 4.9, 16.2, 8.3, 10.7 and 17.5%, respectively. No significant difference was found between individuals sampled before and at the beginning and end of the breeding season. However, late in the season the migration of old spermatids and release of spermatozoa tended to be somewhat retarded, causing a slight increase in the duration and frequency of the last two stages of the cycle.