TROPICAL FAUNAS are distinguished in all the continents by the immense variety of animals which they contain, and in many cases by the brilliancy of their color. Not only are all the principal types of animals represented, bat genera, species, and indi viduals occur in abundant profusion. The tropical is the region of the apes and mon keys (which seem to be naturally associated with the distribution of the palms, whiclk furnish to a great extent the food of the monkeys on both continents), of herbivorous bats, of the great pachyderms, such as the elephant, the hippopotamus, and the tapir, and of the whole family of edentata. Here, too, are the largest of the cats, the lion and the tiger. Among birds, the parrots and toucans are essentially tropical; amongst the reptiles, the largest serpents, crocodiles, and tortoises belong to this zone, as also do the most gorgeous insects. The marine fauna is also superior in beauty, size, and num ber to those of other regions. The tropical fauna of each continent furnishes new and peculiar forms. Sometimes whole types are restricted to one continent, as the sloths, the toucans, and the humming-birds to America; the gibbons, the red orang, the royal tiger, and numerous peculiar birds to Asia; and the giraffe and hippopotamus to Africa; while sometimes animals of the same group present different characteristics on differ ent continents. Thus, for example, the American monkeys have flat and widely sepa rated nostrils, 36 teeth, and generally a long prehensile tail; while the monkeys of the old world have their nostrils close together, only 32 teeth, and non-prehensile tails.
The island of Madagascar has its peculiar fauna. A large number of species of quadrumana, cheiroptera, inseetivora, etc., are found only in this island; and of 112, species of birds that have been described, 65, or more than half, are found nowhere else. We have already referred to the still more exclusive fauna of the Galapagos islands, which has been specially studied by Darwin.
The multiplicity of facts in zoological distribution, which cannot be accounted for by climate, or any other external existing cause, has given rise to various explanations. Until recently, the received theory was that the several species of animals had been originally created in certain spots named specific centers, whence they migrated more or less widely, and that they had existed unchanged throughout the longest succession of generations. This theory was felt from the first to be unscientific; and knowledge of the facts rendered it less and less satisfactory. Other schemes of distri bution, into which the consideration of the Distribution of Life in Past Ages and the Doctrine of 'Evolution largely enter, are accordingly now in favor. Mr. Sclater, followed by Mr. Wallace, divides the earth into six main zoological regions. In one of these, the Palwarctic, consisting of 'the northern portion of the old world, it is held that animal life originated—at least in its higher forms. Each of the other regions, it is argued, i has been at one time or another in connection with this original seat of life, and has received its supply of animals from it by migration. Geological revolutions have gradu ally produced the present state of the earth's surface, and the new conditions of life met by the migrated animals have, in accordance with the theory of evolution, so modified them as to produce the varying fauna of the globe. In those countries which have been longest and most completely separated from each other the difference of animal life will be found greatest.
See the various works of Agassiz; Vogt's Zoologische Briefs, vol. ii.; Mrs. Somer ville's Physical Geography, vol. ii.; Maury's La Terre et l'Homme; linden's Ilancibuciz der Physischen Geographic; Schmarda's great work, Die Geographische Verbreitung der lhiere; and especially The Geographical Distribution of Animals, by A. R. Wallace (1876).