Marsupials
Marsupials have pouches on their abdomen into which their youngs, in immature condition, grow up. These young mammals develop in the pouch and feed on the milk from the mammary glands of their mothers on a first-come-first-served basis. Kangaroos and koalas are marsupials.
Placental Mammals
Mammals such as monkeys, dogs, and cats have placenta in their bodies, hence they are called placental mammals. The placenta is an organ that supplies the young with nutrients from the mother's blood while inside the womb.
