The gonad is the primary reproductive organ of male and female animals, in which develop the gametes or sex cells. Gonads are usually paired organs. In the male the gonad is a testis, which produces sperm. In the female the gonad is the ovary, which produces ova (eggs). A hermaphrodite animal possesses both types.

The activities of the gonads – both male and female – are regulated by gonadotrophin-releasing hormones released by the pituitary gland.