THE EXTERNAL FORM OF WHALES 29 



whales, as a rule, do not swim very fast, and many 

 hairy creatures like the otter do swim with consider- 

 able rapidity. The whales are the most purely aquatic 

 of all mammals, and they are undoubtedly the least 

 hairy ; there seems, therefore, to be some connection 

 between the two facts. But it must be borne in 

 mind that in the Seals and Sea-lions there is an outer 

 coating of fat, and yet the hair is retained, particularly, 

 of course, in the species which furnish the sealskin of 

 commerce, and which possess a soft, thick uncler-fur 

 as well as a coating of coarser hairs. Among aquatic 

 mammals, however, there appearsJLo be an undoubted 

 tendency to lose the hairy covering. Among the 

 Sea-lions some do not possess the soft under-fur which 

 makes the pelages of their allies so valuable ; the 

 hair is with them apparently becoming reduced. Then 

 we have the Sirenia, Manatee, Dugong, in which the 

 hair has almost disappeared. The Walrus is another 

 case in point, and so is the Hippopotamus. But the 

 latter instance is suggestive of another possible 

 reason for the loss of the hairy covering in whales. 

 There are several Ungulate types which have 

 gradually got less hairy in the course of their evo- 

 lution ; the Elephants of to-day contrast, by their 

 almost naked skin, with the Mammoth of the Pleis- 

 tocene ; the modern Rhinoceros is hardly more 

 hairy, except, indeed, the Sumatran species ; while 

 there was, contemporary with the Mammoth, the 

 hairy Rhinoceros. Another division of the Ungu- 

 lates shows the same tendency ; in the pig tribe 

 we have the largely hairless Babyrusa, as well as 



