AQUATIC MAMMALS 



portance in limiting the degree of aquatic specialization of this animal, 

 and it has probably contributed very largely to the fact that the Aus- 

 tralian marsupials, so able in their plasticity to fill all vacant ecologic 

 niches, have never developed an aquatic form, for such bold individuals 

 as dared venture freely into the water would be likely to drown their 

 young and die without issue. At the same time it is possible that dur- 

 ing submergence the pouch might retain sufficient air for the needs of 

 the young. 



u 



FIGURE 3. Some aquatic mammals. Platypus (Ornithorhynchus) (redrawn 

 from Lewin), beaver (Castor), desman (Desmana) (redrawn from Flower 

 and Lydekker), and capybara (Hydrochoerus) (redrawn from Scott). 



INSECTIVORA 



Aquatic insectivores are all small and few of them can venture into 

 deep water for fear of large fish. Hence they must retain in large de- 

 gree their dependence upon the land, for throughout their lives along the 

 rills which they inhabit escape by a scamper through pebbly shallows may 

 be just as necessary as by diving. Aquatic forms have the fur even denser 

 than usual: the tendency is for the hind feet to become enlarged and 

 fringed with bristles as well as to be slightly pronated and for the tail 

 to become keeled with hairs, or (and) flattened horizontally. Rarely 

 have the external ears disappeared. Swimming, except in the aquatic 

 Tenrecidae, is evidently always by alternate strokes of the hind feet as- 

 sisted to some extent by accompanying motions of the tail. 



Talpidae 



Desmana the desman, occurs in southeastern Russia. The fur is 

 especially dense and fine, the snout is long and flattened vertically, and 



[27] 



