Marsupial gestation is extremely short — typically 8–30 days — because marsupials lack a true chorioallantoic placenta. The young (joey) is born at a very early developmental stage and crawls to the mother's pouch (marsupium) where it attaches to a nipple and completes development. For example, Virginia opossum: ~12 days; kangaroos: ~30–36 days. Compare to placental mammals, whose much longer gestation allows more complete foetal development.