CETACEA. 



711 



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. The inspiration and expiration 

 occur at longer intervals than in terrestrial mammals. 

 The water-vapour expelled along with the air from the 

 lungs condenses into a cloud, which is sometimes increased, 

 by an accidental puff of 

 spray. 



The kidneys are lobulated. 

 The testes are abdominal. 

 There are no seminal vesicles. 

 The uterus is bicornuate. 

 The placenta is non-deci- 

 duate and diffuse. The two 

 mammae 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 swal- 

 low cuttles and fish, and 

 Orca attacks other Cetaceans 

 and seals. Most are gregari- 

 ous, and live in 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. 



Certain Eocene fossils, known as Zeuglodonts, are regarded by some 

 (Lydekker, Dames) as primitive Cetaceans — Archaeoceti — less special- 

 ised than modern forms, but Professor D'Arcy Thompson has advanced 

 strong arguments in favour of their affinities with Pinniped Carnivores. 



Fig. 



315. — Pelvis and hind-limb of 

 Greenland whale (Baltena) — After 

 Struthers. 

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



