There is a system of tiny tubes in the testicl*s. These tubes, called the seminiferous tubules, house the germ cells that hormones — including testosterone, the male sex hormone — cause to turn into sperm. The germ cells divide and change until they resemble tadpoles with a head and short tail.
The tails push the sperm into a tube behind the testes called the epididymis. For about five weeks, the sperm travel through the epididymis, completing their development. Once out of the epididymis, the sperm move to the vas deferens.
When a man is stimulated for sexual activity, the sperm are mixed with seminal fluid — a whitish liquid produced by the seminal vesicles and the prostate gland — to form sem*n. As a result of the stimulation, the sem*n, which contains up to 500 million sperm, is pushed out of the penis (ejacul*ted) through the urethra.
