1. The layer of epithelial cells lining the seminiferous tubules of the testis, which gives rise to spermatogonia (see spermatogenesis).

2. A misnomer for the ovarian surface epithelium—a layer of epithelial cells on the surface of the ovary that is continuous with the mesothelium. These cells are involved in repairing defects in the surface of the ovary following ovulation and also are thought to be the source of the granulosa cells of the ovarian follicles. They do not give rise to the ova as was formerly believed.