GEOGRAPHICAL DISTRIBUTION OF MAMMALS 247 



They are found in almost all seas, wandering about over 

 vast areas; but, as a rule, preferring cool or cold waters. 

 The North Pacific, due probably to its great food supply, 

 is a famous place for them. 



How animals become distributed over the globe from 

 their unknown places of origin we know in a general way. 

 Large numbers, as the elk, elephant, buffalo, bison, an- 

 telope, porpoise, prairie dog, and others, live in herds, or 

 schools, and range over vast areas in search of food or to 

 avoid enemies. Others, as squirrels and rats, seem to be 

 seized at times with an irresistible and instinctive desire 

 to migrate, and they move on in vast herds, thousands 

 dying on the way, others being left behind to populate new 

 localities ; and in this way they have become distributed 

 over the continents and islands of the habitable world. 



