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placentalia |
2 definitions found From Webster's Revised Unabridged Dictionary (1913) [web1913]: Placentalia \Plac`en*ta"li*a\, n. pl [NL.] (Zo["o]l.) A division of Mammalia including those that have a placenta, or all the orders above the marsupials. From Webster's Revised Unabridged Dictionary (1913) [web1913]: Mammalia \Mam*ma"li*a\, n. pl [NL., from L. mammalis. See {Mammal}.] (Zo["o]l.) The highest class of Vertebrata. The young are nourished for a time by milk, or an analogous fluid, secreted by the mammary glands of the mother. Note: Mammalia are divided into three subclasses; -- I. {Placentalia}. This subclass embraces all the higher orders including man. In these the fetus is attached to the uterus by a placenta. II {Marsupialia}. In these no placenta is formed, and the young, which are born at an early state of development, are carried for a time attached to the teats, and usually protected by a marsupial pouch. The opossum, kangaroo, wombat, and koala are examples. III. {Monotremata}. In this group which includes the genera {Echidna} and {Ornithorhynchus}, the female lays large eggs resembling those of a bird or lizard, and the young, which are hatched like those of birds, are nourished by a watery secretion from the imperfectly developed mamm[ae].
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