674 WHALES xxvi 



especially the upper one, and the teeth are spade-shaped. The true 

 dolphins, Delphinus (Fig. 441), are larger animals (8 ft), living mostly 

 on fish and having long, many-toothed jaws, the upper forming a beak. 

 They are very fast swimmers, reaching 20 knots. The narwhal, Monodon 

 (Fig. 442), is a large delphinoid (15 ft long) with a single tooth, usually 

 the left upper incisor, remaining in the male and growing continually 



Fig. 442. Narwhal, Monodon. (After Norman and Fraser.) 



Fig. 443. Sperm whale, Physeter. (After Flower and Lydekker, 

 Mammals, Living and Extinct, A. & C. Black, Ltd.) 



Fig. 444. Bottle-nosed whale, Hyperoodon. (After Norman and Fraser.) 



to make the spirally twisted horn, up to 9 feet long, whose use is not 

 known. The female retains a pair of small incisors buried in the 

 premaxillae. 



In the sperm whales, Physeteroidea (Fig. 443), the rostrum is over- 

 laid by an enormous reservoir containing spermaceti, a pure white 

 waxy liquid solidifying in air. Either this, or some other feature, 

 enables them to reach a larger size than other toothed whales (60 It). 

 Sperm whales have functional teeth only in the lower jaw and vestigial 

 ones in the upper. They feed on cephalopods, the remains of whose 

 jaws, combined with solid secretions to make stones in the intestine, 

 form the substance ambergris used as an absorbent in the manufacture 

 of scent. The bottle-nosed whales, such as Hyperoodon (Fig. 444) of 

 polar seas, are also cephalopod feeders and reach 30 ft in length. 



