rsupials. At a much later period--probably in late Tertiary
times--the ancestors of the various species of rats and mice which now
abound in Australia, and which, with the aerial bats, constitute its
only forms of placental mammals, entered the country from some of the
adjacent islands. For this purpose a land connection was not necessary,
as these small creatures might easily be conveyed among the branches or
in the crevices of trees uprooted by floods and carried down to the sea,
and then floated to a shore many miles distant. That no actual land
connection with, or very close approximation to, an Asiatic island has
occurred in recent times, is sufficiently proved by the fact that no
squirrel, pig, civet, or other widespread mammal of the Eastern
hemisphere has been able to reach the Australian continent.

_The Distribution of Tapirs._

These curious animals form one of the puzzles of geographical
distribution, being now confined to two very remote regions of the
globe--the Malay Peninsula and adjacent islands of Sumatra and Borneo,
inhabited by one species, and tropical America, where there are three or
four species, ranging from Brazil to Ecuador and Guatemala. If we
considered these living forms only, we should be obliged to speculate on
enormous changes of land and sea in order that these tropical animals
might have passed from one country to the other. But geological
discoveries have rendered all such hypothetical changes unnecessary.
During Miocene and Pliocene times tapirs abounded over the whole of
Europe and Asia, their remains having been found in the tertiary
deposits of France, India, Burmah, and China. In both North and South
America fossil remains of tapirs occur only in caves and deposits of
Post-Pliocene age, showing that they are comparatively recent immigrants
into that continent. They perhaps entered by the route of Kamchatka and
Alaska, where the climate, even now so much milder and more equable than
on the north-east of America, might have been warm enough in late
Pliocene times to have allowed the migration of these animals. In Asia
they were driven southwards by the competition of numerous higher and
more powerful forms, but have found a last resting-place in the swampy
forests of the Malay region.

_What these Facts Prove._

Now these two cases, of the marsupials and the tapirs, are in the
highest degree instructive, because they show us that, without any
hypothetical bridging of deep o