ve and to evolve slowly along
their own lines in their own restricted southern world, their
collateral descendants in Europe and Asia and America or elsewhere went
on progressing into far higher, stronger, and better adapted forms--the
great central mammalian fauna. In place of the petty phalangers and
pouched ant-eaters of the oolitic period, our tertiary strata in the
larger continents show us a rapid and extraordinary development of the
mammalian race into monstrous creatures, some of them now quite extinct,
and some still holding their own undisturbed in India, Africa, and the
American prairies. The palaeotherium and the deinoceras, the mastodon and
the mammoth, the huge giraffes and antelopes of sunnier times, succeed
to the ancestral kangaroos and wombats of the secondary strata. Slowly
the horses grow more horse-like, the shadowy camel begins to camelise
himself, the buffaloes acquire the rudiments of horns, the deer branch
out by tentative steps into still more complicated and more complicated
antlers. Side by side with this wonderful outgrowth of the mammalian
type, in the first plasticity of its vigorous youth, the older
marsupials die away one by one in the geological record before the faces
of their more successful competitors; the new carnivores devour them
wholesale, the new ruminants eat up their pastures, the new rodents
outwit them in the modernised forests. At last the pouched creatures all
disappear utterly from all the world, save only Australia, with the
solitary exception of a single advanced marsupial family, the familiar
opossum of plantation melodies. And the history of the opossum himself
is so very singular that it almost deserves to receive the polite
attention of a separate paragraph for its own proper elucidation.

For the opossums form the only members of the marsupial class now living
outside Australia; and yet, what is at least equally remarkable, none of
the opossums are found _per contra_ in Australia itself. They are, in
fact, the highest and best product of the old dying marsupial stock,
specially evolved in the great continents through the fierce competition
of the higher mammals then being developed on every side of them.
Therefore, being later in point of time than the separation, they could
no more get over to Australia than the elephants and tigers and
rhinoceroses could. They are the last bid for life of the marsupial race
in its hopeless struggle against its more developed mamm