324 



TYPES OF ANIMAL LIFE 



curved teeth, like a pair of bony straps, that at last 

 curve inward over the upper jaw, the movements of 

 which they must hamper. These whales have the bony 

 support of the upper jaw in the form of a long, cylin- 

 drical bone, or " rostrum," denser than ivory, and such 

 structures, more or less mutilated, are frequently found 

 fossil in Pliocene strata. 



A most curious Arctic cetacean is the " narwhal," or 

 sea unicorn, the latter name having been given to it on 

 account of an enormous tusk which the males develop. 

 The length from head to the end of the tail, without 



FIG. 81. 



THE NARWHAL. 



the tusk, is about fifteen feet, but the tusk itself often 

 attains a length of seven or eight feet The head is 

 short and rounded and the paddles very broad. In 

 colour it is dark grey above, white below, and the whole 

 body is marbled or spotted with blackish, or more or less 

 dark, grey. It feeds on small fishes, cuttle-fishes, and 

 crab-like animals. It has a few irregular rudimentary 

 teeth, but besides them two elongated teeth lie horizon- 

 tally within the upper jaw in the female. In the male 

 one of these, usually the left one, becomes enormously 

 developed, jutting straight outward from the front of 

 the head like a great horn. It is marked with spiral 

 grooves and ridges, and tapers gradually to a point. 



