The mammalia or milk-secreting animals present some of the most distinctive features of the fauna, seen as well in the absence of the huge and striking forms found chiefly in the Old World, as in the presence of a large proportion of peculiar types, not represented elsewhere than in tropical America. Whole groups or families are conspicuous by their absence, such as the man-like apes, baboons and lemurs, the fox-bats, the elephants, the hippopotamus, the rhinoceros, the horses, the giraffe, the camels, the oxen, the sheep, the goats, the antelopes, the bears, the hyaenas, the civet cats, the hedgehogs, and the moles and shrews ; while the families represented by the ring-tail monkeys and the marmosets, the simple leaf-nosed bats, the cavies or guinea-pigs, the sloths, armadillos and ant- eaters, are strictly confined to this tropical region. The families, too, of the racoons and the opossums are almost as characteristic, a single species in each case ranging to the North American region.
The fossil remains of Brazil and La Plata show that formerly the South American Continent was occupied by huge armadillos, sloths and ant-eaters, together with repre- sentatives of the elephants, the horse, the antelope, and many other forms which have become extinct, while representatives of the camels still exist in the Southern temperate regions. With the exception of the three orders of the egg- laying mammals, the elephants, and the hedge-hog and its allies, the mammalia are well represented, and we will briefly consider them according to their orders.