Individual testicle, responsible for some endocrine activity, and responsible for generating spermatozoa. Analogous to the ovary in the female, there are two of these in the adult human male, suspended outside the body in a wrinkled sac of skin, the scrotum, which can contract to bring the testes closer to the body in cold or dangerous conditions. Plural testes.

A testis requires a lower temperature than normal body temperature in order to produce healthy sperm; thus, it is suspended outside the body in the scrotum. During embryonic development, the testes are found inside the abdominal cavity of the embryo, later descending into the scrotum before birth. In some males, one or both testes may fail to descend; a condition known as cryptorchidism or ectopic testis. Such undescended testes become sterile if not artificially placed in the scrotum; they also tend to become cancerous.

In certain individuals, one or both testes may be capable of ascending into the abdominal cavity under pressure or in times of stress.

Mainly composed of about 250 compartments (the lobuli testes), each containing from 1 to 3 seminiferous tubules. While mostly separate, the tubules in adjacent lobules may occasionally intercommunicate. The lobules converge on the mediastinum, where they each produce a small tubule, the caniculari recti which then terminate in the rete testis. The testes are suspended in the scrotum by the spermatic cords.

The testis is enclosed by a thick, firm, white membrane, the albuginea testis, which projects into the testis to form the mediastinum testis. There is an additional membrane covering the albuginea testis, termed the tunica vaginalis propria; these two membranes are separated by a thin cavity, termed the cavitas serosa. Covering the whole of the testis and the epididymis is the tunica vaginalis communis.