Spermatogonial stem cell is a spermatogonium that does not differentiate into a spermatocyte, a precursor of sperm cells. Instead they continue dividing into other spermatogonia or remain dormant to maintain a reserve of spermatogonia. Type B spermatogonia on the other hand, differentiate into spermatocytes which in turn undergo meiosis to eventually form mature sperm cells. During foetal development, gonocytes develop from primordial germ cells and following this SSCs develop from gonocytes in the testis. SSCs are the early precursor for spermatozoa and are responsible for the continuation of spermatogenesis in adult mammals.