Definition of testis. : a typically paired male reproductive gland that produces sperm and secretes testosterone and that in most mammals is contained within the scrotum at sexual maturity.
Failure of a testis to descend into the scrotum is called cryptorchidism. The testis is divided internally into about 250 compartments or lobules, each of which contains one to three small convoluted tubules, within which spermatozoa are produced.
One of the two male gonads, suspended in the scrotum by the spermatic cord. The testis, or testicle, contains the long, coiled seminiferous tubules in which the SPERMATOZOA are formed. Between the tubules are cells that secrete testosterone and other masculinizing steroid hormones and oestrogens.