http://en.wikipedia.org/wiki/Anatomy
Mammals are amniotes, and most are viviparous, giving birth to live young. The exception to this are the egg-layingmonotremes, the platypus and the echidnas of Australia. Most other mammals have a placenta through which the developing foetus obtains nourishment, but in marsupials, the foetal stage is very short and the immature young is born and finds its way to its mother's pouch where it latches on to a nipple and completes its development.
Mammals are amniotes, and most are viviparous, giving birth to live young. The exception to this are the egg-layingmonotremes, the platypus and the echidnas of Australia. Most other mammals have a placenta through which the developing foetus obtains nourishment, but in marsupials, the foetal stage is very short and the immature young is born and finds its way to its mother's pouch where it latches on to a nipple and completes its development.
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