Testicle

**Testis:** (testes, testi, testosterone)

Almost all mammals give birth to live young as small, helpless creatures and feed them with milk. But some species lay eggs with embryos that develop and leave the mother. This is the method of reproduction in reptiles, birds, reptiles (lizards and snakes), and many fish. In mammals, another way of producing offspring is viviparity, when a young animal is born already well developed.