Figure 37.5: The Mammalian Testis (A) Seminiferous tubules fill the testis and continuously produce millions of sperm during the reproductive season. (B) This cross section of a testis shows both a seminiferous tubule and groups of interstitial (Leydig) cells in the spaces between this tubule and adjacent tubules. (C) As germ cells undergo gametogenesis, the cells move from the outer region of the seminiferous tubule toward its center (shown by arrows; compare with Figure 37.4A), where sperm are shed into the lumen of the tubule.