This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubules. These cells are called spermatogonial stem cells. The mitotic division of these produces two types of cells. Type A cells replenish the stem cells, and type B cells differentiate into spermatocytes. The primary spermatocyte divides meiotically Meiosis I into two secondary spermatocytes; each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II.