MAMMALIA. 



403 



Fig. 304. SQUIRREL. 



Geographical Distribution. On this subject Mr. Water- 

 house remarks, that " species of the same group most frequently 

 have a wide range in the same, or nearly the same parallels 

 of latitude; but when 

 the species are inhabi- 

 tants of the high ridges 

 of mountains, they will 

 follow the course of 

 the mountains, though 

 that course may be in 

 the opposite, or north 

 and south direction." 

 We learn from the same 

 authority that the fa- 

 mily of the Squirrels 

 (Sciuridce, Fig. 304)' 

 contains no less than 

 153 species. Few are 

 found in South Ame- 

 rica; they are chiefly 

 natives of the northern 

 parts of that continent. Two, or perhaps three species occur 

 south of the equator, but on the eastern side of the Andes 

 only. They also become rare in the southern parts of the 

 eastern hemisphere. The family (Muridce) to which the Rats 

 and Mice belong, contains 306 species, and has the greatest 

 geographical range. That to which the Porcupine is referred 

 (Hystricidce) is, on the contrary, essentially American. " Out 

 of about eighty-seven species appertaining to this family, seven 

 only are found out of the South American province, and these 

 belong to the most highly organised divisions of the family." 

 The groups of islands comprehended under the term Polynesia, 

 have no representatives of the present order, except such as 

 there is reason to believe have been introduced by shipping. 



If instead of considering the Rodentia with reference to the 

 great divisions of the globe, we limit our view to their dis- 

 tribution within the British Isles, we shall find that, out of 

 fourteen species enumerated by Professor Bell, seven, or one 

 half of the entire number are absent from Ireland. This 

 is a singular fact when we consider how small an arm of the 

 sea separates the two countries. The annexed figure (305) 

 represents one of the Voles, little animals, which in many 



