50G ZOOLOGY 



Seals {Otariidm) and Walruses {Trichecliidm), being unable to flex the 

 thigh forwai-ds under the body so that the hind-limbs may aid in 

 supporting the weight, and thus being only able to drag themselves 

 along very awkwardly when on dry land. The pinna of the ear is 

 absent in the Earless Seals and Walruses, well developed in the 



Fig. 1121, — Seal {Plioca vifulina) 



Eared Seals. The surface in all is covered with a thick, soft fur. 

 In the Fur-Seals there are two kinds of hairs — those of the one 

 kind being longer and coarser, and scattered through the more 

 numerous shorter and finer hairs composing the fur proper. A 

 remarkable feature of the Walruses is the presence of a pair of 

 large tusks — the enlarged canine teeth — projecting downwards 

 from the upper jaw. 



Some of the Rodents (Beavers, Water- Voles) are aquatic and 

 some (Squirrels and Tree-Porcupines) are arboreal, while others 

 (the majority of the order) lead a terrestrial life, and are active 

 burrowers ; they are on the whole a very uniform group, and 

 exhibit few such remarkable modifications as are to be observed in 

 some of the other orders of Mammals. They are nearly all furry 

 animals, with plantigrade or semiplantigrade limbs, usually five-toed. 

 The tail is usually elongated, and may be naked or covered with fur ; 

 but sometimes, as in the Rabbits and Hares, it is very short. A 

 few special modifications, however, have to be noted in certain 

 families of Rodents. The Flying Squirrels have on each side a 

 fold of skin, the patagium, which serves as a parachute. The 

 African Flying Squirrels {Anomalwnis) are remarkable also on 

 account of the presence of a series of overlapping horny scales on 

 the lower surface of the basal part of the tail. The Jerboas {Dipus) 

 and their allies are characterised by the great relative length of 

 the hind-limbs — the mode of locomotion of these remarkable 

 Rodents being by a series of leaps not unlike those of the 

 Kangaroo — and by the reduction of the number of the toes to 

 three in some of them. The Porcupines {Hystricidce) have 

 numerous elongated spines or " quills " among the hairs of the 



