MAMMALIA. 



3S7 



tig. 304.— Sqdibbei. 



Georjraphical Distribution .—On this subject Mr. Waterhouse 

 remarks, that " species of the same group most frequentlv have 

 a wide range in the same, or nearly the same parallels o"f lati- 

 tude ; but when the 

 species are inhabitants 

 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 

 {S ■ /(fa?, Fig. 304) 



...ains no less than 

 153 species. Few are 

 found in South Ame- 

 rica ; they ai'e 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 hemi.sphere. The 

 family [Mui-idce) to which the Rats and Mice belong, contain.^ 

 30t) species, and has the greatest geographical range. That to 

 which the Porcupine is referred {Hi/stricida;) is, on the con- 

 trary, essentially American. " Out of about eighty-seven 

 species appertahiing to this family, seven only are found out 

 of the South American province, and those belong to the most 

 highly organized divisions of the family." The groups of 

 islands comprehended under the term Polynesia, have no re- 

 presentatives 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 o4ir view to their distri- 

 bution within the British Isles, we shall find that, out of four- 

 teen 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) repre- 



2 c 



