ORDER SCIORIDJ2; SQUIRREL, PTEROMYS. 251 



especially buds and young shoots in the spring and summer, and 

 nuts, acorns, &c. in the autumn and winter, it spends nearly 

 its whole time amongst trees, leaping from branch to branch with 

 great agility, and seldom descending to the ground, except 

 for the purpose of passing to another tree. They are usually 

 found in pairs, which pairs are believed to associate for life ; and 

 they construct little spherical nests, near the tops of the highest 

 trees, by weaving twigs together, leaving an opening at the top. 

 In such places, they and their young are out of the reach of all 

 quadruped foes; but they occasionally become the prey of 

 ravenous birds, when these roam on the wing over the forests 

 they inhabit. Some species of Squirrel associate in large 

 numbers ; and others so far resemble the next family, as to form 

 their nests by burrowing amongst the roots of trees. As already 

 mentioned, the business of the tail is the peculiar characteristic 

 of the Squirrel tribe ; and this is of great assistance to them in 

 leaping ; for not only does the tail serve to guide them, but even 

 to give them a degree of support, its hairs spreading out sideways, 

 when the animal is in motion, into a sort of feathery expansion. 



FIG. 126. FLYING SQUIRREL. 



In the Pteromys, or Flying Squirrel, this sustaining power is 

 much increased, by an extension of the skin of the flank between 

 the fore and hind legs ; and this, with the tail, forms a kind of 

 parachute, on which the agile little animals are sustained in 

 their long leaps from bough to bough, the first impulse being 

 given by their powerful hind-legs. But, as elsewhere explained, 



