有袋目

[ noun ]
coextensive with the subclass Metatheria
<noun.animal>

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].


Marsupialia \Mar*su`pi*a"li*a\
(m[aum]r*s[=u]`p[i^]*[=a]"l[i^]*[.a]), prop. n. pl. [NL., fr.
L. marsupium a pouch, bag, purse, Gr. marsy`pion, dim. of
ma`rsypos, ma`rsipos.] (Zo["o]l.)
A subclass of Mammalia, including nearly all the mammals of
Australia and the adjacent islands, together with the
opossums of America. They differ from ordinary mammals in
having the corpus callosum very small, in being implacental,
and in having their young born while very immature. The
female generally carries the young for some time after birth
in an external pouch, or marsupium. Called also {Marsupiata}.