74 A BOOK OF WHALES 



among existing Cetacea, their shapes remain for con- 

 sideration. As a rule the teeth of whales are simple 

 and conical in form, directed either upwards or, rather, 

 forwards. They resemble in fact the canine teeth of 

 other mammals, not only in this shape, but in their 

 being implanted by a single root. 



There are, however, a few examples of some, though 

 not a great deal of, specialisation in the form of the 

 teeth. In Inia Geoffrcnsis the posterior series of 

 teeth have a distinct lateral cusp, so that they have 

 ceased to be simply peg-like teeth. In the common 

 Porpoise, Phocana communis, the teeth have broad 

 divided crowns, which are sharply marked off from 

 the root ; there is a reminiscence here of the more 

 complicated teeth of ancestral forms, such as the 

 Zeuglodonts. The extraordinary strap-shaped teeth 

 of Mesoplodon layardi (see p. 220) and the tusks of 

 the Narwhal need not be referred to in the present 

 connection ; they appear to be simply exaggerations 

 (perhaps originally pathological) of the simple con- 

 ditions obtaining in other whales ; they are probably 

 not to be looked upon as an inheritance from terres- 

 trial ancestors. 



Professor Kukenthal has a theory that the simple 

 teeth of whales are to be derived from the splitting 

 up of more complicated teeth, such as are found in 

 other mammals. In Zeuglodonts (called so on this 

 very account) each tooth is formed of two pieces, 

 each with its separate root. By division of these 

 the more numerous teeth of a dolphin can be arrived 

 at. But recent investigations into the Manatee seem 



