OF THE CLASS MAMMALIA. 265 



the length of the tail, furnished with hairs like a large quill 

 or feather. They live amongst trees on fruits and nuts, and 

 are remarkable for their agility. There are many species 

 in the Old and New Worlds. In France the common squirrel 

 ahounds, and retains throughout the year the colour for 

 which it is known; but in the North it becomes, during 

 winter, of a fine ashy-blue colour, and the fur is much 

 sought after. In this state the fur is called petit gris. 



Fig. 207. The Jerboa. 



The beaver is distinguished from all other rodents by its 

 large tail, flattened horizontally ; it is of an oval form, and 

 covered with scales. The beaver is of a good size, aquatic in 

 its habits ; their feet and tail aid them in swimming, and 

 with their powerful cutting teeth they easily cut down all 

 sorts of trees. They live on bark and other hard vegetable 

 substances. 



The Canadian beaver is, of all quadrupeds, that which 

 exhibits most industry in the construction of its dwelling, 

 at which it works in society, in the most solitary parts of 

 North America ( 331, p. 164). 



The neighbourhood of man seems to prevent the beaver 

 from working in society, as we find that the beavers of the 

 Rhine are solitary, and never construct habitations like those 

 of Canada, although they seem to belong to the same species. 



