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Webster 1913 Edition
Mammalia
‖
Mam-ma′li-a
,Noun.
pl.
[NL., from L.
mammalis
. See Mammal
.] (Zool.)
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.
☞ 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 mammae.