THE EVOLUTION OF MAN 



more solid even than that of the trout and her- 

 ring. It is evidently a separate adaptation. The 

 connecting link following the Ceratodus class is 

 found below the entire class of bony fish which 

 are once again a special side line. 



The Ceratodus class of fish have still other 

 conspicuous relations to fish of the sturgeon class. 



A LAMPREY, 



the representative of a group of fish intermediate between the 

 Amphioxus type and the Sharks. 



The historical evidence coincides with these 

 marks, for sturgeons were present in extraordi- 

 narily large numbers during the Primary age. 

 In fact, there were so many species of them that 

 they represented for a while the entire fish family 

 on this earth. Wherever we see in museums 



106 



