Synopses & Reviews
Synopsis
Excerpt from A Critical Period: In the Development of the Horse
In the opossum, and the vast-majority of the marsupials, the young are born in a very immature condition - as soon as they are able to seize and hang on to the teats. These ancient forms have not discovered that, by utilising the allantois (originally a breathing organ), they might considerably prolong the protection afforded by the uterus 1 that when the yolk sac fails, by throwing out root-like processes from the allantois, they might tap an almost inexhaustible food supply. But all the higher forms (the Eutheria) utilise the allantois, and some of them are already so perfect at birth that the time may come when the milk glands (very old-fashioned organs), so essential to the marsupials, may in some cases be entirely, or almost entirely, dispensed with.
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