The scrotum is a sac that hangs under the penis and holds the
testes. It is divided internally into two halves by a membrane; each half
containing a testis. It has an outer layer of thin, wrinkled skin over a layer
of tissue which contains muscle. The testicle lies inside the scrotum and
produces as many as 12 trillion sperm in a male's lifetime, about 400 million of
which are ejaculated in one average intercourse.
Each sperm takes about
seventy-two days to mature and its maturity is overseen by a complex interaction
of hormones. The scrotum has a built-in thermostat, which keeps the sperm at the
correct temperature. It may be surprising that the testicles should lie in such
a vulnerable place, outside the body, but it is too hot inside. The sperm
production needs a temperature which is three to five degrees below body
temperature. If it becomes too cool on the outside, the scrotum will contract to
bring the testes closer the body for warmth.