777 /<; MOUSE 



443 



the workl, seem ' to show ii transition to the marine forms, such 

 as the dolphins, the toothed whales (Fit>;. 401), and the tooth- 

 less or wlialeljone whal(>s. The lai'gest of these whales — 

 the Greenland whale — reachcss an extreme length of twenty- 

 two to twenty-four metres, and a weight of over 100,000 kilo- 

 grammes. It is, indei'd, the largest living animal. Although 



Fk;. 401. — The killer whale, Orca. After True. 



whales in general are partly adapted to an aquatic life, they 

 still retain the essential mammalian qualities. They breathe 

 air which passes to the lungs and is expelled again through the 

 nostrils, which are placed high up on the head. The " l:ilow- 

 ing " of the whale is the forcible expiration of moi.sture-laden 

 air, which becomes visible by condensation, just as our own 

 breath does on a cold day. The young are necessarily born in 

 the water, but the breeding habits are poorly known. The 

 various Cetacea have diverse feeding habits. All are preda- 

 ceous. The toothed whales feed on larger animals, the whale- 

 bone whales on floating fish, crustaceans, medusae, and squids ; 



' The relation to Cetacea is not close. 



