2 8 A BOOK OF WHALES 



in others, there are hairs in the foetus, but none in 

 the adult animal. These hairs are, however, entirely 

 limited, in every case, to the jaw region, and are 

 so few that they can be, and have been, counted. 

 Thus in the common Porpoise there are but two on 

 each side in the foetus. The adult Bal&noptera borealis 

 has, according to Dr. Collett,* twenty-six. Some ad- 

 ditional facts will be found below in the systematic 

 part of the present volume. The most noteworthy 

 point, however, about these hairs, next to the scarcity 

 of them, is the fact that they seem to be in all cases 

 rudimentary. A careful investigation of the struc- 

 ture of the skin has shown Dr. Kukenthal that the 

 hairs of whales are entirely without those small 

 glands associated with the hairs in other mammals, 

 and secreting an oily matter for the lubrication of 

 the hairs ; these sebaceous glands, as they are termed, 

 are not found in Cetacea at all. Their absence clearly 

 denotes a degeneration in the hairs. 



Now the question arises, Is this loss of hair a 

 matter of aquatic life ; is it in any way connected 

 with their aquatic existence ; or has it some other 

 explanation ? The usual view, of course, is that 

 the hair is absent as not necessary to an aquatic 

 animal ; the use of hair is largely that of retaining 

 the heat of the body. The loss of heat in whales 

 is prevented by the thick covering of blubber as 

 well as by the thickness of the skin itself. Thus 

 a hairy covering would be unnecessary, and, perhaps, 

 even in the way, though this is not so clear. For 



* Proc. Zool. Soc.) 1886, p. 255. 



