CHAPTER III 



Order : CETACE^. WHALES AND PORPOISES 



As our review of the British mammalian fauna only commences 

 with the human period — that is to say, the Pleistocene division of 

 the Tertiary Epoch — when most existing mammalian species were 

 developed or developing, no mention will be made here of our 

 long extinct monotremes and marsupials. The first order (on 

 the upwards list) represented in the British fauna is that of the 

 Whales. 



The Cetacea are an order of purely aquatic mammalia, so 

 absolutely adapted to life in the water that it is impossible for them 

 to live and move out of their element. Yet their lives must be 

 spent for the most part near the surface, since they are as much 

 dependent on a supply of air for the oxygenation of their blood as 

 are any of the other mammalia. Any member of the Whale order 

 can be drowned if prevented from renewing its supply of air. 

 Some cetaceans cannot remain under the surface of the water for 

 more than an hour without rising to renew their supply of air, 

 though it is said that some of the larger cetaceans (such as the 

 rorqual whales) can remain below the surface for as much as twelve 

 hours without expiring from lack of air. Whales are further dis- 

 tinguished from all other mammals (except the Sirenia) by their 

 complete loss of all external vestiges of hind limbs. In all whales 

 there are minute fragments of bones found isolated in the muscles 

 of the lower part of the body which represent the disappearing 

 structure of the hind limbs, but these vestiges at most only extend 

 as far as a fragment of the thigh bone and sometimes of the tibia 

 (one of the leg bones), all traces of the feet being completely 



n 2 



