MAMMALS IN THE WATER 237 



water, but it shows that the rat is quite at home in that 

 element. The rat has no structural adaptation of any 

 kind to help him, and the water-vole is to all appearance 

 the same in structure as the land-vole. That there 

 should be so little modification is quite contrary to 

 the ancient and established view that if an animal can 

 swim and dive it must be like a duck or a fish. When 

 Fuller was writing of the ' natural commodities ' of 

 Cardiganshire, he remarked : * What plenty there was 

 of beavers in this country in the days of Giraldus ; the 

 breed of them is now quite destroyed, and neither the 

 fore- foot of a beaver (which is like a dog's) nor the 

 hind-foot (which is like a goose's) can be seen therein.' 

 But the performances of the creatures, which are little 

 or not at all changed in structure, are perhaps more 

 interesting from the personal point of view of their 

 human critics than those of animals like the seals, 

 walruses, and whales, whose legs have turned into fins. 

 Their experiences and difficulties in the water ought to 

 be somewhat like our own. The surprising point is 

 that most forms of movement in the water seem to 

 present to them no difficulty at all. Very young otters 

 are ' taught ' to go into the water, and so, presumably, 

 are the young duckbills, which lie in a subterranean nest 

 for several weeks before entering the water. But the 

 young otters at the Zoo were hauled out by their 

 mothers when they stayed in too long. They swam 



