218 MOSTLY MAMMALS 



to the martens and weasels, but specially modified for the 

 needs of an aquatic life, and furnished with teeth adapted 

 to seize and hold the slippery prey on which they subsist. 

 Since, however, they are much less exclusively aquatic 

 than seals, spending much of their time on shore, their 

 structural variations from the ordinary mammalian type 

 are far less marked than is the case in the members of 

 the latter group. The toes, for instance, are not webbed, 

 and neither pair of limbs shows a tendency towards a 

 paddle-like form, although both are relatively short. In 

 addition to this shortening of the limbs, the points chiefly 

 noticeable as adaptations for swimming are the great breadth 

 and flatness of the head, the small size of the ears, the 

 absence of a distinctly defined neck, the elongated and 

 flattened body, moderately long and powerful tail, and the 

 denseness and softness of the fur. As regards the teeth, 

 it will suffice to mention that while these conform to the 

 general marten type, the hinder ones are remarkable for 

 the greater extent of grinding surface, the last upper molar 

 especially being distinguished by the peculiarly squared 

 form of its crown. In all these teeth the cusps are re- 

 markably strong and sharp, and thus suited for piercing 

 the scales of fish. 



Contrast these features with those distinctive of the sea- 

 otter — which, by the way, is the only representative of 

 its kind. In addition to its being a shorter- and thicker- 

 bodied creature, with a still broader muzzle and no 

 definable neck at all, the sea-otter is at once distinguished 

 by the structure of its hind-feet, which are fully webbed, 

 and so lengthened and expanded as almost to simulate 

 paddles ; the extremities of the toes being, it is said, 

 turned down beneath the sole when on land. The tail, 

 too, is thicker, less tapering, and more flattened than that 



