Studying marsupial immune function

There are three groups of living modern day mammals - the Eutherians, commonly called the placentals; the Metatherians or marsupials and the Prototherians or monotremes. These three groups differ primarily in their reproductive strategies. Eutherian mammals give birth to well-developed young that are nourished in-utero by a placenta throughout gestation whilst, in general, Metatherians have a comparatively short gestation time that results in the birth of immature young. These young typically develop in an external pouch during a long lactation period that may last for up to 300 days in some species. The evolutionary separation of Eutheria and Meta theria is believed to have occurred between 75 and 150 million years ago. Prototherian mammals, represented by the echidna (family Tachyglossidae) and the platypus (family Omithorhynchidae ), are clearly distinguished from the other mammalian groups by their characteristic egg- laying ability.