birthplace and subsequent migrations of the more important genera and families; and thus obtain some conception of that grand series of co-ordinated changes in the earth and its inhabitants, whose final result is seen in the forms and the geographical distribution of existing animals. {50}CHAPTER IV. ON ZOOLOGICAL REGIONS. To the older school of Naturalists the native country of an animal was of little importance, except in as far as climates differed. Animals were supposed to be specially adapted to live in certain zones or under certain physical conditions, and it was hardly recognised that apart from these conditions there was any influence in locality which could materially affect them. It was believed that, while the animals of tropical, temperate, and arctic climates, essentially differed; those of the tropics were essentially alike all over the world. A group of animals was said to inhabit the "Indies;" and important differences of structure were often overlooked from the idea, that creatures equally adapted to live in hot countries and with certain general resemblances, would naturally be related to each other. Thus the Toucans and Hornbills, the Humming-Birds and Sun-Birds, and even the Tapirs and the Elephants, came to be popularly associated as slightly modified varieties of tropical forms of life; while to naturalists, who were acquainted with the essential differences of structure, it was a never-failing source of surprise, that under climates and conditions so apparently identical, such strangely divergent forms should be produced. To the modern naturalist, on the other hand, the native country (or "habitat" as it is technically termed) of an animal {51}or a group of animals, is a matter of the first importance; and, as regards the general history of life upon the globe, may be considered to be one of its essential characters. The structure, affinities, and habits of a species, now form only a part of its natural history. We require also to know its exact range at the present day and in prehistoric times, and to have some knowledge of its geological age, the place of its earliest appearance on the globe, and of the various extinct forms most nearly allied to it. To those who accept the theory of development as worked out by Mr. Darwin, and the views as to the general permanence and immense antiquity of the great continents and oceans so ably developed by Sir Charles Lyell, it ceases to be a matter of surprise that the tropics of Africa, Asia, and America should differ in their productions, but rather that they should have anything in common. Their similarity, not their diversity, is the fact that most frequently puzzles us.