Seminiferous tubule. Light micrograph of a cross section through a seminiferous tubule in a testis. The tubule (oval) is lined by a complex, stratified layer of seminiferous epithelium. The process of sperm production occurs in waves along the length of the tubule. The germ cells, the spermatogonia, are found in the basal layer of the epithelium (black dots). These cells undergo a series of divisions to become sperm with tails (at centre of tubule). Leydig cells (brown, outside the tubule) produce the hormone testosterone. Magnification: x100 at 35mm size.