CETACEA. 



707 



has rarely a cajcum, the hver is but slightly lobed, there is 

 no gall bladder. 



The heart is often cleft between the ventricles. Both 

 arteries and veins tend to form retia mirabilia. 



The larynx is elongated so that it meets the posterior 

 nares, and forms a continuous canal down which air passes 

 from nostrils to lungs. Cetaceans must, of course, rise to 

 the surface to inspire, but the expiration occurs at longer 

 intervals than in terrestrial mammals. The water vapour 

 expelled along with the air from the lungs, condenses into 



a cloud, which is some- 

 times increased by an 

 accidental puff of spray. 



The kidneys are lobu- 

 lated. The testes are ab- 

 dominal. There are no 

 seminal vesicles. The 

 uterus is bicornuate. 

 The placenta is non- 

 deciduate and diffuse. 

 The two mammffi lie in 

 depressions beside the 

 genital aperture, and the 

 milk is squeezed from 

 special reservoirs into the 

 mouth of the young. 

 Usually a single young 

 one is born at a time, 

 and there are never more 

 than two. 



All are carnivorous, but 

 while many feed on small 

 pelagic animals, others 

 swallow cuttles and fish, 

 and Orca attacks other 

 Most are gregarious and live in 



Fig. 260. — Pelvis and hind-limb 

 of Greenland Whale (Balaena). 

 (After Struthers.) 



P., Pelvis ; F., femur ; T., tibia. 



Cetaceans and seals, 

 schools or herds. 



The living Cetaceans are ranked in two sub-orders — the 

 Mystacoceti or Balsenoidea without functional teeth but with 

 whalebone or baleen plates on the palate, and the Odontoceti 

 or Delphinoidea, with functional teeth and without baleen. 



