They are warm-blooded, but their temperature
is much lower than that of other mammals, and varies appreciably
with the temperature of their surroundings.* Their apparatus for
suckling the young is primitive. There are no teats, and the milk
is forced by the mother through simple channels upon the breast,
from which it is licked by the young. The Anteater develops her
eggs in a pouch. They illustrate a very early stage in the
development of a mammal from a reptile; and one is almost tempted
to see in their timorous burrowing habits a reminiscence of the
impotence of the early mammals after their premature appearance
in the Triassic.
* See Lucas and Le Soulf's Animals of Australia, 1909.
The next level of mammal life, the highest level that it attains
in Australia (apart from recent invasions), is the Marsupial. The
pouched animals (kangaroo, wallaby, etc.) are the princes of
pre-human life in Australia, and represent the highest point that
life had reached when that continent was cut off from the rest of
the world. A few words on the real significance of the pouch,
from which they derive their name, will suffice to explain their
position in the story of evolution.
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