The testes (singular: testis) are a pair of male reproductive organs located within the scrotum, a pouch of skin and muscle that hangs outside the male body. The primary function of the testes is to produce sperm (spermatogenesis) and secrete the male sex hormone testosterone. Here are the key features and functions of the testes:

1. Sperm Production (Spermatogenesis): The testes are responsible for producing sperm cells, which are the male gametes (reproductive cells). Spermatogenesis is a complex process in which diploid germ cells (spermatogonia) undergo a series of divisions and transformations to become mature haploid sperm cells (spermatozoa).
2. Hormone Production: The testes secrete the male sex hormone testosterone. Testosterone plays a crucial role in the development of secondary sexual characteristics in males, such as facial and body hair, deepening of the voice, and increased muscle mass. It also influences libido (sex drive) and contributes to the overall maintenance of male reproductive health.
3. Temperature Regulation: The testes are located outside the body in the scrotum because sperm production is temperature-sensitive. The slightly lower temperature in the scrotum compared to the body’s core temperature is essential for the proper maturation and storage of sperm. When it’s too hot, the scrotum relaxes and moves the testes away from the body; when it’s too cold, the scrotum contracts and brings the testes closer to the body to maintain the ideal temperature for sperm production.
4. Semen Production: Although the testes themselves do not produce semen, the sperm they produce, when mixed with other fluids from the seminal vesicles, prostate gland, and bulbourethral gland, form semen. Semen is ejaculated from the male reproductive system during sexual intercourse and serves as a vehicle for sperm delivery.

The testes are vital for male reproduction and the maintenance of male sexual characteristics and function. Issues or diseases affecting the testes can have significant consequences for male fertility and overall health. Common conditions that can affect the testes include testicular cancer, infections, and hormonal disorders. Regular self-examinations and medical check-ups can help in the early detection of potential problems related to the testes.