(A) All of the stages of spermatogenesis shown take place while the developing gametes are in intimate association with Sertoli cells, which are large cells that extend from the basal lamina to the lumen of the seminiferous tubule; they are analogous to follicle cells in the ovary. Spermatogenesis depends on testosterone secreted by Leydig cells, located between the seminiferous tubules. (B) Dividing spermatogonia are found along the basal lamina. Some of these cells stop dividing and enter meiosis to become primary spermatocytes. Eventually sperm are released into the lumen. In man it takes about 24 days for a spermatocyte to complete meiosis to become a spermatid and another 5 weeks for a spermatid to develop into a sperm. Sperm undergo further maturation and become motile in the epididymis and are only then fully mature sperm.