PLANT-EATING MAMMALS 



177 



that the thumb is much reduced in size. The cheek-teeth are 

 possessed of roots, and though both squirrels and dormice are 

 mainly vegetarian, they also raid birds'-nests for the sake of the 

 eggs and young. 



BEAVERS (Castorida) deserve mention as regards their food, 

 which consists of roots, bark, and young wood. They can even 

 cut down trees by means of their immensely strong incisors, 

 and do a great deal of damage in this way. Their cheek-teeth 

 are more complex than in the forms so far mentioned, being 

 better provided with enamel folds. 



True RATS and MICE (Murid<z) are omnivorous in habit, but 

 many of their immediate allies are herbivorous. This is the 

 case, for example, with the mouse-like Field-Voles (Arvicola), 

 which sometimes play havoc with growing crops, even destroy- 

 ing their roots by burrowing, as also with the larger Hamsters 

 (Cricetus) and Lemmings (My odes]. Hamsters are among those 

 rodents possessed of cheek-qouches, serving for temporary storage 

 of food, and in this case particularly large. 



A very interesting family is that of the MOLE-RATS (Spala- 

 cidce], of which a typical representative is the Great Mole- Rat 



Fig. 424. The Common European Mole-Rat (Spalax typhlus) 



(Spalax typhlus] (fig. 424) of South-east Europe, South-west Asia, 

 and Egypt. It has elsewhere been pointed out that adaptation to 

 a particular mode of life results in corresponding specialization 



VOL. II. 



