THE RODENTS, 
253 
well-formed ears, the Hudson Bay lemming {Ciinicidus 
torqiiatus) has no external ears. It becomes pure white in 
winter, while the lemmings do not change. It inhabits 
the arctic regions of Asia and Europe as well as arctic 
America and Greenland. In summer it burrows under 
stones in dry ridges, and in the winter nests in the moss. 
Fia. 293. — Flying Squirrel (Sciuropterus volans), one half natural size. 
From their nest-building habits, rodents are, as a rule, not 
unlike birds; and Owen, for these reasons, ascribes to them 
a low degree of intelligence. Granting that this is the 
case, an exception to this rule is seen in the social beavers, 
which evince a high, exceptional degree of intelligence. 
Beavers build a dam in a running stream so as to create an 
