How the Body Works Immature Male Sex Cells Immature sex cells, or spermatogonia, in the testes divide by mitosis and become primary spermatocytes. Each one then divides by meiosis, a cell division peculiar to the reproductive organs, to form two secondary spermatocytes, each containing half the full number of chromosomes. A second meiotic division splits each spermatocyte into two spermatids, which then mature into sperm.