The organ of sperm production. In addition, the testis (testicle) is an organ of endocrine secretion in which male hormones (androgens) are elaborated. In the higher vertebrates (reptiles, birds, and mammals), the testes are paired and either ovoid or elongated in shape. In mammals, the testes are usually ovoid or round. In many species (for example, humans) they are suspended in a pouch (scrotum) outside the main body cavity; in other species they are found in such a pouch only at the reproductive season; in still others the testicles are permanently located in the abdomen (for example, in whales and bats).