684 COLLEGE ZOOLOGY 



Sweden, where ordinarily none live, and in a year or two multiply 

 into hordes which go traveling straight west toward the Atlantic, 

 or east toward the Gulf of Bothnia, as the case may be, regard- 

 less of how the valleys trend, climbing a mountain instead of 

 going around it, and, undeterred by any river or lake, keep per- 

 sistently onward until finally some survivors reach the sea, into 

 which they plunge and perish." They are said to march in 

 " parallel lines three feet apart " and " gnaw through hay and 

 corn stacks rather than go round." (Pennant.) 



/. Domesticated Mammals 



The most common domesticated mammals are the dog, horse, 

 ass, ox, sheep, goat, pig, and cat. The dog was probably the 

 first mammal to be domesticated. Dogs have been the com- 

 panions of man for many centuries; they have become changed 

 while under domestication, until there are now more than two 

 hundred breeds. In many cases local wild species of the genus 

 Canis have been tamed; for example, the original Arctic sledge 

 dogs were half-tamed gray wolves, and the dogs kept by our 

 northwestern Indians were tamed coyotes. 



The immediate ancestors of the horse are not known, and there 

 are at the present time no wild horses from which it could have 

 arisen. It has probably developed from animals inhabiting the 

 semiarid plains of central Asia. The more remote ancestors 

 of the horse are well known (see Chap. XXII). 



The ass is the favorite beast of burden in Eastern countries. 

 In this country the cross between a female horse and male ass is 

 known as a mule. The common ass of Europe and America is 

 descended, through the early Egyptian domestication, from 

 the African wild ass, Equus africanus. 



The oxen of Europe and America were probably derived from 

 the aurochs, Bos primigenius, of Europe. The sacred or humped 

 cattle of India, Bos indicus, doubtless developed from one of 

 the wild races that still roam the Himalayan foot-hills. 



Sheep have been domesticated for so many centuries that their 



