99 



CHAPTER XVII. 



CLASSIFICATION OF MAMMALS continued. 



6 1. Order 7, Cetacea (Whales). These, like the 

 Sirenia, are marine mammals with no hind limbs, and 

 having the fore limbs converted into fins. They are 

 fish-like in shape, without necks, and have a smooth 

 thick skin beneath which is a thick layer of fat known 

 as blubber. The nostrils are situated on the upper 

 surface of the head, and are called blow-holes, and 

 are well protected by dermal folds so as to prevent 

 the entrance of water into the air-passages while 

 the whale is beneath the surface of the sea. These 

 animals require to rise to the surface to breathe, and 

 on doing so they forcibly eject a shower oi spray, 

 consisting of the mucus secreted by the membrane of 

 the nasal passages, the vapour of the breath, and 

 whatever sea water lurks in the crevices about the 

 nostril ; this process is called blowing, and it is in 

 reality somewhat like a forcible sneeze preparatory to 

 a deep inspiration. The sense of smell is almost or 

 altogether absent. There are seven cervical vertebrae, 

 but they are usually united together so as, in old 

 whales, to form one bone. 



The tail in whales consists of two lateral, hori- 

 zontally-placed lobes consisting of folds of skin and 

 connective tissue appended to the end of the vertebral 

 column ; this is the chief instrument of locomotion. 



The mouth in true whales is of enormous capacity, 

 and as theii food is mostly small fish, cuttlefishes and 



