42 CETACEANS 



the females both tusks remain in a similar rudimentary condition. The developed 

 tusk of the male is composed solely of ivory, and its spiral twist always runs from 

 left to right. In form it is cylindrical, and tapers more or less markedly from root 

 to tip. Not unfrequently the tusk attains a length of from 7 to 8 feet, or more 

 than half that of the entire animal. Very rarely narwhals are met with in which 

 the right tusk is developed as well as the left, but there appears to be no known 

 instance of the right tusk being developed while the left remains rudimentary ; and 

 it is noteworthy that when the right tusk is developed it has the same left-to-right 



A SCHOOL OF NARWHALS ( 5 n liat. size). 



twist as its fellow. A fine narwhal's skull with two tusks is preserved in the 

 Cambridge Museum. Apart from a few small rudimentary ones, which are 

 irregular in their occurrence, the male narwhal has no teeth except the tusk, 

 while the female save for similar rudiments is toothless. 



Although the presence of the tusk in the male narwhal, and the practically 

 toothless condition of the female, are alone sufficient to distinguish the genus from 

 all other dolphins, it is necessary to say something further regarding the form and 

 structure of this singular animal. In the first place, the narwhal belongs to a group 

 of dolphins characterised by their blunt and rounded heads, in which the muzzle 

 shows no sign of being produced into a beak. A special character of the animal is 

 to be found in the absence of a back-fin, which is represented merely by a low and 



