EVOLUTION AND EXTERNAL APPEARANCE 83 



coot', we might equally well say that he is as 'bald as a whale'. Cetacean 

 skin is as smooth as glass, and we know that the smoother, for instance, the 

 hull of a boat, the greater its speed, and that barnacles can greatly impede 

 its progress. In fact. Cetaceans have no need of hair, since hair (or clothing) 

 by surrounding the body with a layer of still air, acts as a thermal insulator 

 \vhich prevents rapid cooling or heating. Now, if water enters the hair (or 

 the clothing) the thermal effect is lost at once. True, aquatic animals 

 which regularly come ashore, such as seals, and sea lions, have a short- 

 haired fur, but to Cetaceans, who always remain in the sea, fur would 

 merely be an impediment. It might be argued that apart from being a 

 thermal insulator, hair also offers protection against injury from sharp 

 objects with which terrestrial animals may often collide. But then such 

 sharp objects rarely exist in the ocean (as distinct from the ocean bed). 



Connected with this lack of hair, there is also a lack of sebaceous glands. 

 These small glands which secrete a fatty substance, are usually attached 

 to the hair follicles, and protect the skin from flaking or the hair from 

 splitting. Now a dry skin is something a whale need not bother about in its 

 norinal habitat, but when living specimens of dolphins or porpoises are 

 transported overland to an aquarium, great care must be taken to keep 

 them wet all over, for otherwise they will most certainly perish through 

 injury to their skin. (We might just mention here that Cetaceans also lack 

 sweat glands, but we shall return to this subject at greater length in 

 Chapter ii.) When we say that whales are completely hairless, we are 

 not, strictly speaking, correct. In fact, the Greenland Whale has about 

 250 bristles on its chin and the tip of its upper jaw. Rorquals have a total 

 of 50-60 hairs : one row along the edge of the upper jaw, and another on 

 either side of the axis of this jaw - from the tip of the snout to just behind 

 the blow-hole (Fig. 43). Dolphins generally have no more than 2-8 hairs, 

 usually close to the tip of the snout. In some species, e.g. the Sperm Wliale, 

 hair is only found during foetal development, while the Narwhal and the 

 Beluga have no hair at any stage. In any case, what few hairs Ceta- 

 ceans have are not really 'hairs' so much as 'vibrissae' -just like a cat's 

 whiskers. They are tactile organs, rather than fur (cf. Chapter 9), and 

 therefore have a special structure. Not only are they stiffer, but the 

 follicles are surrounded with greatly distended veins, the so-called blood 

 sinuses, and with a great nuinber of nerve endings whose structure is 

 identical to that of tactile corpuscles. No less than four hundred nerve 

 fibres run to every hair. Now we can understand why the Cetaceans have 

 bristles over their jaws, for this is precisely where vibrissae are normally 

 found in terrestrial animals also. We do not know what it is that Cetaceans 

 feel with their hair, but it is unlikely to be very important or else the hair 

 would be longer. 



