The seminiferous tubules are the site of the germination, maturation, and transportation of the sperm cells within the male testes. Seminiferous tubules are made up of columnar Sertoli cells surrounded by spermatogenic cells on the epithelial interior and stem cells exteriorly. Spermatogenesis through the process of meiosis takes place within the thin seminiferous tubules, which loop tightly throughout the testes to a tremendous length (perhaps as much as a mile between the two testes) within more than 200 compartments divided by fibrous septa of the tunica albuginea. Stem cells on the exterior of the tubules divide through mitosis then proceed inward and transform on the interior walls of the seminiferous tubules, giving rise to the germinal sperm cells (spermatogonia), which slowly flow through the seminiferous tubes for up to 60 days or more toward the central tubule on the way to the web-like rete testes at the upper back of the testes and then through the efferent ductules to the epididymis for storage on the exterior of the testes. Along the way, the maturing sperm cells receive nutrients and raw materials from the vascular Sertoli cells located in the tubule walls until they become mature primary sperm cells (spermatozoa). Spermatozoa are not entirely complete in their maturation upon leaving the seminiferous tubules, having still to develop the tails that give them their motility.