If you’ve ever watched a television courtroom drama, you know that defendants on the stand swear on the Bible before testifying. But in ancient Rome, men placed their right hands somewhere else—over their testes, according to some classical scholars. This may explain why the male gonads are named for the Latin word testis, or “witness.” Truth-telling abilities aside, this set of plumshaped organs’ role in the body is to produce sperm and male hormones, called androgens.

Because sperm need a temperature of 97°F (2° lower than the normal body temperature) in order to grow, the testes reside in a scrotal sac that hangs from the body. Located behind the penis and in front of the anus, the scrotum has a built-in thermostat. If the body becomes too cold—from jumping in a chilly pool, for example—the cremasteric muscles in the scrotum pull the testes closer to the body for more warmth.

Also known as a testicle, each testis weighs less than an ounce and measures about an inch in diameter. Inside the scrotum, a thin, blue white membrane called the tunica albuginea surrounds each testis. Within this membrane, fibrous tissue partitions the interior into 200 to 400 wedge-shaped sections, or lobes. Each individual lobe contains up to 10 tubules, where the sperm develop; these tubules make up about 90 percent of a testicle’s mass. Growing between the tubules are cells that secrete the all-important androgens, including testosterone. These hormones are responsible for driving the male reproductive system.

ADDITIONAL FACTS

  1. In animals that mate only during certain times of the year, such as sheep and goats, the testes descend from the body during breeding season; this process is called recrudescence.
  2. Men who frequently perch laptop computers on their laps may have reduced fertility, because the heat from the computer can raise the scrotum’s temperature.
  3. Each year in Throckmorton, Texas, there is a World Championship Rocky Mountain Oyster Festival, at which people cook—and eat—bull testicles. One of the contests is a “tastes like chicken” event.