GEOGRAPHICAL DISTRIBUTION OF ANIMALS 1539 



the most part, from those of other regions. The ani- 

 mal life of the Old World is markedly different from 

 that of the New World in correspondent parallels, 

 and under conditions of climate which are in all im- 

 portant regards analogous. Even when the genera, or 

 families, are the same, the species are in nearly all 

 cases distinct. In yet higher measure, the animal 

 life of Australia differs from that of other divisions 

 of the globe. Whole orders of the animal world are 

 wanting in Australian zoology, while the vast major- 

 ity of its animals belong to a division which is alto- 

 gether unrepresented in the continents of the Old 

 World that is, the marsupial tribe. The difference 

 is less strongly marked in the case of the adjacent con- 

 tinents of the Northern Hemisphere than in the in- 

 stances of the lands lying south of the equator. 



The natural distribution of animals has been im- 

 portantly modified by human agency. This is espe- 

 cially the case in regard to those divisions of the 

 mammalia which comprehend the domestic quadru- 

 peds the horse, dog, ox, sheep, and others. Man 

 has carried these animals with him in his migrations 

 from one region to another, and has thus introduced 

 new species (and even genera) into lands where they 

 were previously unknown. The horse, the ox, and 

 the common sheep, were unknown in the New World 

 prior to the Spanish discoveries of the Fifteenth and 

 Sixteenth Centuries, but speedily became naturalized 

 there, and, in the case of the two first-named, have 

 long since reverted to a condition of nature. Wild 

 horses roam by thousands over the savannas and 

 pampas of the western world. Within a much more 



