THE CETACEA, OR WHALES. 



253 



Dolphin species. We do not speak of the dolphin- 

 like whales with reduced dentition e.g. the Nar- 

 whales ; these are side branches of the main stem, 

 the members of which are distinguished by numer- 

 ous teeth of the same shape. The teeth are always 

 growing -and have no closed roots, wherein they 

 resemble those of many of the reptiles. Now 

 Baume, for various 

 good reasons, has 

 made it seem probable 

 that the ever-growing 

 teeth of mammals are 

 an ancient inherit- 

 ance, and that rooted 

 teeth, on the other 

 hand, are a new ac- 

 quisition. If Baume 

 is right in this, we 

 have no connecting 

 link for the Dolphins, 

 and naturally none either for the Whalebone whales. 

 All the three subdivisions Zeuglodonta, Dolphins, 

 and Whalebone whales are found side by side in 

 the Early Tertiary period, and the vertebrae of 

 whales have even been found in the Jura. How- 

 ever, all that can be said with certainty is that we 



FIG. 47. Tooth of Squalodon. 



a, From the outside ; 6, from the side. 

 After SUss. 



