CHAPTER XIV 

 ZOOGEOGRAPHY 



Zoogeography is the phase of zoology which deals with the distribu- 

 tion of animals on the earth. It is sometimes spoken of as the geograph- 

 ical distribution of animals or as animal geography. Some of the more 

 striking general facts regarding this distribution, and the agencies to 

 which it must be attributed, are discussed in this chapter. 



FACTS OF DISTRIBUTION 



The general fact of zoogeography, that there are great differences in 

 the distribution of animals, is obvious even to those who have not 

 studied the subject and whose acquaintance with animals is very Hmited. 

 Even to the uninitiated it is known that certain animals have a rather 

 definite range, or region in which they are characteristically found, and 

 that they are absent from other places. North America does not support 

 elephants, except in captivity; the lion-hunter goes to Africa; polar 

 bears are much more common sights to the Eskimos than to men farther 

 south; and the jungles of India maintain an animal population unlike 

 that of the wildest regions of the new world. With the diversified data 

 which wider experience affords, these differences of range are greatly 

 multiplied, and may be of a wholly different nature. However, the 

 facts of distribution are not in chaos, but may be arranged in a somewhat 

 orderly fashion. Many of the differences in distribution may be grouped 

 into five categories: (1) differences in the geographic position of the 

 ranges, (2) differences in their size, (3) differences in their continuity, (4) 

 differences in the physical conditions prevailing in them, and (5) differ- 

 ences in the proximity of the ranges of apparently related forms. 



Differences in Geographical Position. — It is probable that with the 

 exception of species related as closely as parasite and host no two kinds of 

 animal have exactly the same range. At any rate there are great differ- 

 ences in geographical position. The musk-ox, for example, is an arctic 

 species; the nine-banded armadillo occurs in South America and Middle 

 America and southern Texas; and the North American alligator is con- 

 fined to the extreme southeastern part of the United States. These 

 examples are from widely different groups. Such differences, however, 

 are also to be found within the same group, even in groups of as low 

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