Men can continue to produce new sperm by the vas deferens from puberty to death. Once the sperm leave the testes they enter the parietal testes. Each parotoid contains a long series of highly twisted tubes that, as they pass, undergo a maturation process that gives the sperm the ability to move forward. The sperm then enter the vas deferens, each of which, rising along the posterior edge of the testes, crosses the inguinal canal into the pelvic cavity, where they bypass the sides of the bladder and stop behind the bladder, connecting the ejaculatory ducts to the urethra. The sperm pool in the vas deferens and wait for ejaculation to push the sperm into the urethra. Behind the bladder is a pair of ejaculatory ducts, which are formed by the convergence of the ducts of the seminal vesicles and the vas deferens. The seminal vesicles secrete an alkaline, viscous fluid in the seminal fluid that is rich in fructose. Just below the bladder, wrapped around the upper part of the urethra, is the prostate gland, shaped like a chestnut. The prostate gland secretes an acidic fluid that flows to the urethra from a tube near the ejaculatory duct. Below the prostate, on either side of the urethra, are paired urethral glands, about the size of a pea, which secrete mucus. Sperm move from the testes by ciliary oscillation and contraction of the ducts, and sperm do not swim on their own until ejaculation. It takes about seventy-four days for the sperm to be conceived in the testes, mature in the epididymis, and pass through the vas deferens. When a man is sexually aroused, the urogenital glands secrete mucus to lubricate the urethra, and at the same time, ejaculation may occur. Therefore, it is possible for sperm to appear in the fluid prior to ejaculation. At the time of ejaculation, the opening between the bladder and urethra is closed. At this time, sperm mixed with fluid secreted by the seminal vesicles and prostate gland is called semen, and is discharged from the urethra during orgasm and penile muscle spasms. The amount of semen is about a small tablespoon, containing 120 to 600 million spermatozoa. But even with this amount of sperm, it is smaller than a drop of semen. About one-third of semen comes from the prostate gland, and about two-thirds from the seminal storage vesicles, as well as secretions from endocrine glands. The color of semen varies from person to person and is usually either white, yellow or gray milky and slightly viscous. Once ejaculated, semen that is in a liquid state will quickly turn into a jelly-like consistency when exposed to air. It then liquefies in about 5 to 30 minutes.