CHAP. IV.] ZOOLOGICAL REGIONS. 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 appear- 
ance 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 incommon. Their similarity, not their diversity, 
is the fact that most frequently puzzles us. 
The more accurate knowledge we have of late years obtained 
of the productions of many remote regions, combined with the 
greater approaches that have been made to a natural classifica- 
tion of the higher animals, has shown, that every continent or 
well-marked division of a continent, every archipelago and 
even every island, presents problems of more or less complexity 
to the student of the geographical distribution of animals. If 
we take up the subject from the zoological side, and study any 
family, order, or even extensive genus, we are almost sure to 
meet with some anomalies either in the present or past distri- 
bution of the various forms. Let us adduce a few examples of 
these problems. 
Deer have a wonderfully wide range, over the whole of Europe, 
Asia, and North and South America; yet in Africa south of 
the great desert there are none. Bears range over the whole of 
Europe, Asia, and North America, and true pigs of the genus 
Sus, over all Europe and Asia and as far as New Guinea; yet 
both bears and pigs, like deer, are absent from Tropical and 
South Africa. 
Again, the West Indian islands possess very few Mammalia, 
all of small size and allied to those of America, except one 
