A spermatogonium is a male germ cell along the basement membrane of the seminiferous tubule in the testis that divides by mitosis. When spermatogonia stop dividing mitotically and enter meiosis, they become spermatocytes. There are different types of spermatogonia at different stages of differentiation, and some undifferentiated spermatogonia are the stem cells of the male germ line.