The formation and development of spermatozoa. Spermatogenesis in humans begins with the spermatogonium, the diploid cell that undergoes mitosis to form new spermatogonia as well as cells called primary spermatocytes. Each primary spermatocyte then undergoes the first meiotic division to produce two secondary spermatocytes. Each secondary spermatocyte undergoes the second meiotic division to produce two nonmotile cells called spermatids. The four spermatids then develop flagella and become sperm. Since some of the original spermatogonia replace themselves, the males are able to produce large numbers of sperm continuously after sexual maturity.
