Sperm develop inside the testicles of males. The cell from which sperm develop is called a spermatogonium which divides into spermatocytes. Spermatids emerge from spermatocytes. Over time, spermatids grow a tail which can aid in mobility and eventually it will develop a mature spermatozoa. Spermatozoa can move through the ducts of the testicles and epididymis where it can be ejaculated through the semen.