seminiferous tubules, and secretion of male sex hormone, produced in the interstitial cells. Sperm cell production in the seminiferous tubules is dependent on the normal descent of the testes into the scrotum. In the scrotal sac, the temperature is generally around 2¬°C cooler than in the abdominal cavity. Only at this lower temperature can the germinal epithelium of the seminiferous tubules generate sperm, beginning at puberty.
If the testes do not descend, the germinal epithelium will gradually degenerate. Tiny ducts carry the mature sperm from the tubules to the epididymus, a very coiled tube located on the surface of each testis. The epididymus stores the mature but, as yet, non-motile sperm. During sexual arousal, the epididymes produce secretions that carry the sperm into the two vasa deferentia or sperm ducts. Each vas deferens passes from its epididymus, through its inguinal canal, and over the bladder to join with the urethra immediately after the urethra arises from the bladder. Three sets of glands secrete fluids which combine with the sperm to form semen. The seminal vesicles meet the vasa deferentia just before their junction with the urethra. The prostate gland secretes into the urethra just after its junction with the sperm ducts. The Cowper's glands empty into the urethra as it reaches the base of the penis. The urethra passes through the penis and carries the semen to the outside. In vertebrate males, then, the urethra is used during both the excretory and reproductive processes. Only in vertebrate females are the two processes carried out
