DISTRIBUTION OF THE FAUNAS. 199 



424. Still, the climate is not sufficiently warm over the 

 whole extent of this zone to allow the trees to retain their 

 foliage throughout the year. At its northern margin, the 

 leaves, excepting those of the pines and spruces, fall, on the 

 approach of the cold season, and vegetation is arrested for a 

 longer or shorter period. Insects retire, and the animals 

 which live upon them no longer find nourishment, and are 

 obliged to migrate to warmer regions, on the borders of the 

 tropics, where, amid the ever-verdant vegetation, they find 

 the means of subsistence. 



425. Some of the herbivorous Mammals, the Bats, and 

 the reptiles which feed on insects, pass the winter in a state 

 of torpor, from which they awake in spring. Others retire 

 into dens, and live on the provisions they have stored up 

 during the warm season. The Carnivora, the Ruminants, 

 and the most active portion of the Rodents, are the only ani- 

 mals that do not change either their abode or their habits. 

 The fauna of the temperate zone thus presents an ever- 

 changing picture, which may be considered as one of its 

 most important features, since these changes recur with equal 

 constancy in the Old and the New World. 



J 



426. Taking the contrast of the vegetation as a basis, and 

 the consequent changes of habit imposed upon the denizens 

 of the forests, the temperate fauna has been divided into 

 two regions ; a northern one, where the trees, except the 

 pines, drop their leaves in winter, and a southern one, where 

 they are evergreen. Now, as the limit of the former, tlmt 

 of the deciduous trees,' coincides, in general, with the limit 

 of the pines, it may be said that the cold region of the tem- 

 perate fauna extends as far as the pines. In the United 

 States this coincidence is not so marked as in other regions, 

 inasmuch as the pines along the Atlantic coast extend into 

 Florida, while they do not prevail in the Western States ; 

 but we may consider as belonging to the southern portion 



