6i8 THE WONDER OF LIFE 



the flipper-type must have arisen de novo in the Cetaceans. 

 It is a speciaUzed transformation of a typical mammaUan 

 hmb, just as the skull is a speciaUzation of a typical mam- 

 mahan skull. 



(2) Although the divergence of Cetaceans from a terres- 

 trial stock must have taken place very long ago, the loss 

 of hair may have been very gradual, or it may have occurred 

 brusquely, by a mutation such as we see in ' Chinese dogs '. 

 It is a remarkable fact that they seem never to disappear 

 altogether. Although the inexperienced eye may see none, 

 there is probably no species entirely without them. Dr. 

 Arnold Japhen recently examined five kinds of baleen 

 whales and six kinds of toothed whales, and found hairs 

 about the hps of them all. Therefore we must admit that 

 the capacity of forming hairs remains still in the Cetacean 

 skin, that, in some way or other, the potentiahty of hairs 

 persists as a dwindUng reKc as part of the inheritance. It 

 is very interesting to find that apart from their great reduc- 

 tion in number, the hairs show distinct signs of retrogression. 

 The hair- muscles and the sebaceous glands have gone, 

 the hair shaft is greatly reduced, what is called the root- 

 sheath is simpler than usual, and there is no hair casting. 



(3) On the other hand, we find in regard to whales' 

 hair an illustration of what has often occurred in the 

 course of evolution — ^that vestigial structures may be 

 utiUzed, indeed specialized, even when they are very 

 much reduced. It seems, metaphorically speaking, as 

 if the organism sometimes saved its historical rehcs just 

 as they were disappearing by discovering some utihtarian 

 vindication of them. For these small retrogressed hairs 

 on the whales' Ups exhibit at the same time a remarkable 

 specialization, namely in their rich supply of nerve-fibres 



