ralia and Tasmania--with one
representative of the latter in New Guinea, which seems to have been
still connected--are semi-reptilian survivors of the first animals to
suckle their young. Like the reptiles they lay tough-coated eggs
and have a single outlet for the excreta, and they have a reptilian
arrangement of the bones of the shoulder-girdle; like the mammals, they
have a coat of hair and a four-chambered heart, and they suckle the
young. Even in their mammalian features they are, as the careful
research of Australian zoologists has shown, of a transitional type.
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.

Among the reptiles the task of the mother ends, as a rule, with the
laying of the egg. One or two modern reptiles hatch the eggs, or show
some concern for them, but the characteristic of the reptile is to
discharge its eggs upon the warm earth and trouble no further about its
young. It is a reminiscence of the warm primitive earth. The bird and
mammal, born of the cooling of the earth, exhibit the beginning of
that link between mother and offspring which will prove so important an
element in the higher and later life of the globe. The bird assists the
development of the eggs with the heat of her own body, and feeds the
young. The mammal develops the young within the body, and then f