The testes are the primary sex organs, or gonads, of a male. The gonads of both males and females produce the sex cells, known as gametes, and produce sex hormones. In a male, the gametes are spermatozoa, commonly called sperm cells or sperm. The primary male sex hormone is testosterone.


The testes are housed outside of the pelvic cavity in the scrotum, a sac of skin posterior to the penis. Optimum sperm production occurs below core body temperature, so the scrotum provides a lower temperature environment for the testes.

Each testis is surrounded by two membranes. An outer membranous coating called the tunica vaginalis covers the anterolateral surface. Deep to the tunica vaginalis, the tunica albuginea is a tough, fibrous encasement that forms the outer layer of the testis. Extensions of the tunica albuginea called septa penetrate into the testis and divide the organ into about 250 segments called lobules.

Each lobule contains at least one seminiferous tubule. A seminiferous tubule is a hollow, highly twisted tube that produces sperm cells through a process called spermatogenesis. Sperm produced within the seminiferous tubules are delivered to the rete testis.

Interstitial cells fill in the space outside of the seminiferous tubules. Although these cells do not directly contribute to sperm cell production, they are vital to the male reproductive system because they produce the hormone testosterone.

Figure 1: A sagittal view of an illustration of the testis. The ducts of the testis are continuous with the epididymis and ductus deferens. The ductus deferens as well as blood vessels and nerves are connected to the testis via the spermatoic cord.