Testicles

Testicles. The two testicles are normally carried in the scrotum—a double sac divided by a membrane. Each testicle is about the size and shape of the female ovary. Its main structure is a mass of tiny, coiled tubes in which the male reproductive cells, called sperm cells, are produced. The new sperm move off into [...]

Fertilization of the Egg

Millions of sperm begin the journey, but a comparative few reach the tiny egg in the oviduct. Some sperm attach to the membrane, which covers the egg, and activate it, so that finally one sperm may enter and fertilize. The one sperm that enters the egg loses its tail, which is absorbed, and its head [...]