testis

testis or testicle , one of a pair of glands that produce the male reproductive cells, or sperm . In fetal life the testes develop in the abdomen, then descend into an external sac, the scrotum. A testis is composed of about 800 coiled seminiferous tubules whose linings contain cells that develop into sperm. These tubules merge into a larger tube called the epididymis that leads out of the testis into the vas deferens. Between the seminiferous tubules there is interstitial tissue that secretes the male sex hormone testosterone , which stimulates the development of the male reproductive system and secondary sex characteristics. Sometimes the testes do not descend normally before or shortly after birth and remain in the abdomen or groin. Such a condition requires medical attention or the gland will eventually become sterile. See also reproductive system .

testis (pl. testes) Male sex gland, found as a pair located in a pouch, the scrotum, external to the body. The testes are made up of seminiferous tubules in which sperm are formed and mature, after which they drain into ducts and are stored in the epididymis prior to being discharged.

testis (testicle) The reproductive organ in male animals in which spermatozoa are produced. In vertebrates there are two testes; as well as sperm, they produce steroid hormones (see androgen). In most animals the testes are within the body cavity but in mammals, although they develop within the body near the kidneys, they come to hang outside the body cavity in a scrotum. Most of the vertebrate testis is made up of a mass of seminiferous tubules, lined with Sertoli cells, in which the sperms develop (see spermatogenesis). It is connected to the outside by means of the vas deferens. See reproductive system.