Spermatogenesis in the immature mouse proceeds faster than in the adult.

The first appearance of spermatogenic cell types related to the age of the animal was studied in sections and tubular whole mounts of testes of normal mice (Cpb-N strain) up to 34 days pp. The first intermediate spermatogonia and leptotene spermatocytes were seen at days 4 and 7 p.p., respectively. It was found that the subsequent types of spermatogenic cells appear earlier than could be expected if spermatogenesis was to proceed at adult speed. [3H]thymidine labelling studies revealed that within a given interval of time, spermatocytes and spermatids in immature mice develop into more advanced cell types than in adults. The labelling studies and the observation that the cellular associations are always identical to those in the adult, indicate that the rate of acceleration in young mice is the same for spermatogonia, spermatocytes and spermatids. The mean duration of the cycle of the seminiferous epithelium during the age interval of 10 to 30 days p.p. is 7.51 +/- 0.10 days, compared to 8.61 +/- 0.08 in the adult. It increases gradually towards the adult level, reaching the value of 8.45 +/- 0.17 days between days 33 and 56 p.p.