Most mammals nourish their developing babies in the womb through an organ called the placenta. Marsupials do not have this organ.
In marsupials, the baby is born at a very early stage of its development, and is usually only a few millimetres long. The baby makes its way slowly up the mother’s stomach and crawls into a protective pouch. The baby attaches itself to a teat through which it receives milk while it develops. As the baby grows larger it is able to leave the pouch, returning to feed. Marsupials are said to be more primitive than most other mammals. However, they are highly successful in Australia where they have been isolated from invasion by other animals and have survived for millions of years.
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