The pouch is a distinguishing feature of female marsupials (and rarely in the males as in the water opossum and the extinct thylacine); the name marsupial is derived from the Latin marsupium, meaning "pouch". Marsupials give birth to a live but relatively undeveloped fetus called a joey. When the joey is born it crawls from inside the mother to the pouch. The pouch is a fold of skin with a single opening that covers the nipples. Inside the pouch, the blind offspring attaches itself to one of the mother’s nipples and remains attached for as long as it takes to grow and develop to a juvenile stage.