最終更新日：2022/12/24
Placental mammals that gestate their young internally, as do we and most of the pelts we know, account for 95 percent of the world’s 5,600 species of mammals, and marsupials like the kangaroo, koala and our very own opossum, whose young are born at a grublike stage and do most of their developing externally, often in a pouch, constitute nearly all the rest.
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Placental
mammals
that
gestate
their
young
internally,
as
do
we
and
most
of
the
pelts
we
know,
account
for
95
percent
of
the
world’s
5,600
species
of
mammals,
and
marsupials
like
the
kangaroo,
koala
and
our
very
own
opossum,
whose
young
are
born
at
a
grublike
stage
and
do
most
of
their
developing
externally,
often
in
a
pouch,
constitute
nearly
all
the
rest.
