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 remained almost completely isolated; and, being free from the competition of higher forms, they have developed into the great variety of types we now behold there. These occupy the place, and have to some extent acquired the form and structure of distinct orders of the higher mammals—the rodents, the insectivora, and the carnivora,—while still preserving the essential characteristics and lowly organisation of the marsupials. 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.

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