Mature sperm cells are stores in the tail of the epididymis.The epididymis should be visible at the base of the testicles, and is an Indication of optimal semen production.The idea size of a walnut (Fry,2003)
Where there is no epididymis visible on either testicle, this is an indication of subfertility.Overly large epididymis,however, may be a sign of in jury or infection