Sperm develop in the testes in coiled tubes called seminiferous tubules. Diploid cells that begin the process are located near the outer wall of the tubules (at the top of the enlarged wedge of tissue in figure 27.4A). These cells multiply constantly by mitosis, and each day about 3 million of them develop into primary spermatocytes, the cells that undergo meiosis. Meiosis I of a primary spermatocyte produces two secondary spermatocytes, each with the haploid number of chromosomes (n).The chromosomes are still in their duplicated state, each consisting of two identical chromatids. Meiosis II then forms four cells, each with the haploid number of single-chromatid chromosomes. A sperm cell develops from each of these haploid cells and is gradually pushed toward the center of the seminiferous tubule. From there it passes into the epididymis, where it matures and becomes motile. Sperm are stored in the epididymis until ejaculation