What is the difference between a mammal and a marsupial?
In marsupials, the developing embryo is isolated from its mother’s body by the amniotic membrane. Following fertilization the embryo becomes a new organism, and the mother’s auto-immune system will attack it. The amniotic membrane isolates the embryo from all biological interaction with the parent, thus protecting it from attack. However, no nutrients cross the barrier either, and therefore its growth in the uterus is limited to the quantity of nutrients contained within the egg. The short gestation period in marsupials is due to this type of yolk-type reproduction. Marsupial embryos do not receive nutrients from their mother. Birth in marsupials occurs much earlier in comparison to placental mammals, and the almost helpless fetus journeys to the pouch and becomes attached to a teat for weeks or months depending on the species. Marsupials may spend as few as twelve days in the reproductive tract. A longer gestation period results in offspring that are born more fully developed. The ext
