9-11. PRIMARY SEX ORGAN--TESTIS
The testis is the primary sex organ (gonad) of the male
a. Location. Each male has a pair of testes located within the scrotum. The
scrotum is a sac suspended from the inferior end of the trunk, between the thighs. Each
testis is within a separate serous cavity within the scrotum.
(1) Migration. Originally, testes develop within the posterior abdominal
region of the body. However, during development, they "migrate" out of the body cavity,
through the inguinal canal of the abdominal wall, and into the scrotum.
(2) Temperature control. For the production of mature sperm (spermatozoa),
the testes must be at a temperature that is a few degrees lower than that of the body
cavity. For this reason, the testes are located outside of the body cavity.
(a) Under cold conditions, each testis is pulled up toward the body by the
cremaster muscle. At the same time, the dartos muscle of the scrotal wall contracts and
thus reduces the exposed surface area and thickens the wall.
(b) Under warm conditions, these structures are "relaxed." This allows
the scrotum with the testes to hang free.
(c) If a boy baby is born with undescended testes (either in the
abdominal cavity or inguinal canal) and if nothing is done to bring the testes into the
scrotum, he will be sterile.
b. Production of Spermatozoa. Millions of spermatozoa (male gametes) are
produced by the seminiferous tubules of the testis.
SEMEN = seed
FER = to carry
The male sex hormones (androgens) are also produced by cells of the testes.
9-12. SECONDARY SEX ORGANS
In general, the secondary sex organs of the male are responsible for the
transport and care of the spermatozoa.
a. Epididymis. The spermatozoa pass from the seminiferous tubules into the
tubular structure known as the epididymis. The epididymis is a very long tube, but it is
coiled and attached to the surface of the testis in the scrotum. As the spermatozoa
pass along the length of the epididymis, they are nurtured by the secretions of the