672 



WHALES 



of production or use. Tursiops in a tank recognize the sex of a new 

 arrival in another tank, out of sight. Several such social reactions have 

 been reported, for example, between mother and young. Tursiops can 

 also avoid obstacles in the dusk and since they react to frequencies up 

 to 120 kc/sec it is possible that they emit these for echolocation. 



Fig. 438. Blue whale, Balaenoptera. (After Mackintosh and Wheeler.) 



Fig. 439. Killer-whale, Orcinus. (After British Museum Guide.) 



Fig. 440. Porpoise, Phocaena. (After British Museum Guide.) 



Fig. 441. Dolphin, Delphinus. (After British Museum Guide.) 



The head of odontocetes carries an organ known as the 'melon', 

 which is possibly a receptor. It is a mass of fat in front of the nostril, 

 traversed by muscle-fibres and richly innervated by the trigeminal. It 

 may serve to detect pressure changes in the water, substituting for the 

 vibrissae of seals. In the sperm whale it is enormous (p. 674). 



The behaviour of whales is undoubtedly elaborate, involving social 

 life, communication by sound, and probably much learning. There is 

 cooperation between individuals in helping to keep a wounded com- 

 panion or a new-born at the surface. Play is common and rhythmical 



