Light microscopy of human testis from a sterile individual in which spermatogenesis is absent and sperm are not found in the ejaculate. The seminiferous tubules have lost their normal seminiferous epithelium (of germ cells) and retain only Sertoli cells. This condition can occur in cryptorchid testes (undescended), in some cases for which there are specific gene mutations but also where there is no known cause. Note the over-abundance of Leydig cells that may possibly arise in response to local intratesticular factors, or clustering due to tubule shrinkage. Magnification x100 when printed at 10 cm.