, they seemed destined to
attain at once the domination of the earth. Then, as we saw, the
land was revelled once more until its surface broke into a fresh
semi-tropical luxuriance, and the Deinosaurs advanced to their triumph.
The mammals shrank into a meagre and insignificant population, a
scattered tribe of small insect-eating animals, awaiting a fresh
refrigeration of the globe.

The remains of these interesting early mammals, restricted, as they
generally are, to jaws and teeth and a few other bones that cannot
in themselves be too confidently distinguished from those of certain
reptiles, may seem insufficient to enable us to form a picture of their
living forms. In this, however, we receive a singular and fortunate
assistance. Some of them are found living in nature to-day, and their
distinctly reptilian features would, even if no fossil remains were in
existence, convince us of the evolution of the mammals.

The southern continent on which we suppose the mammals to have
originated had its eastern termination in Australia. New Zealand seems
to have been detached early in the Mesozoic, and was never reached by
the mammals. Tasmania was still part of the Australian continent. To
this extreme east of the southern continent the early mammals spread,
and then, during either the Jurassic or the Cretaceous, the sea
completed its inroad, and severed Australia permanently from the rest of
the earth. The obvious result of this was to shelter the primitive life
of Australia from invasion by higher types, especially from the great
carnivorous mammals which would presently develop. Australia became, in
other words, a "protected area," in which primitive types of life were
preserved from destruction, and were at the same time sheltered from
those stimulating agencies which compelled the rest of the world to
advance. "Advance Australia" is the fitting motto of the present human
inhabitants of that promising country; but the standard of progress has
been set up in a land which had remained during millions of years the
Chinese Empire of the living world. Australia is a fragment of the
Middle Ages of the earth, a province fenced round by nature at least
three million years ago and preserving, amongst its many invaluable
types of life, representatives of that primitive mammal population which
we are seeking to understand.

It is now well known that the Duckbill or Platypus (Ornithorhyncus)
and the Spiny Anteater (Echidna) of Aust