The testis is the primary sex organ (gonad) of the male.
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.
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.
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.
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.
Under warm conditions, these structures are "relaxed." This allows the scrotum with the testes to hang free.
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.
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.