AQUATIC MAMMALS 



glands of the skin whereby there will be secreted just the correct amount 

 of suitable substances to hinder the pelage in becoming water-logged but 

 yet insufficient for the matting of the coat. All aquatic insectivores have 

 this type of pelage, most rodents have it or seem to be in process of ac- 

 quiring it, and it is a character of some of the aquatic carnivores. It is 

 not to keep it warm that the Potomogale of tropical Africa has an un- 

 dercoat almost as fine and heavy as the Siberian desman, but for the 

 purpose of protecting its skin from detrimental action of the water dur- 

 ing prolonged submersion, or to accomplish flotation with the aid of 

 the air imprisoned in the fur. Among aquatic rodents the most notable, 

 and indeed only, example of the lack of an undercoat of fine fur is the 

 capybara, whose pelage is markedly coarse. Like all rodents of Cavidae 

 affinity its coat was probably coarse to begin with and the easier line to 

 follow was to modify its skin rather than its pelage. 



But there are other considerations concerned with the pelage of an 

 aquatic mammal. In the case of a mammal of small or even moderate 

 size the presence of a coat of fine fur whose surface is plastered smooth 

 by the action of the water is doubtless not an appreciable reducer of 

 speed, but although perhaps not impossible it is at least unlikely that a 

 large whale could ever have had the velvety covering of a sea otter, and 

 were a hairy covering present it would doubtless be of wiry texture, 

 which would act as a definite retardant of progression comparable to a 

 weedy growth upon the hull of a vessel. 



Yet another possibility must receive consideration. The Cetacea and 

 Sirenia are the most completely hairless of marine mammals and they 

 are the only ones which can not come ashore to bask and dry their hides. 

 If they had coats of coarse hair it seems almost a certainty that during 

 continuous immersion they would than accumulate such a crop of para- 

 sites and sessile marine growth that life would be unbearable for the 

 wretched creatures ; and resulting scaly and scabby condition of the hide 

 would then inevitably eliminate the hair. The pinnipeds can occasionally 

 haul out upon a rock or the ice, thoroughly dry the hide and remove at 

 least such unwelcome attendants as need continued immersion. The 

 northern fur seal, however, spends many months on its annual migra- 

 tion far from land, and the sea otter very seldom leaves the water, so 

 that the beautiful, soft pelage of these two mammals refutes any im- 

 plication that frequent drying is requisite to the retention of hair in all 

 aquatic mammals. 



Among the pinnipeds there are three types of body covering, repre- 

 sented by the walrus, which is almost hairless, the majority of earless 



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