34 THE SKULL THEORY 



Sharks, are onthe whole the creatures which throw the 

 clearest light on the history of the lineage of the ver- 

 tebrata and on the organisation of our primeval fish- 

 natured ancestors. It is one of the particular merits 

 of Gegenbaur that he clearly and firmly estab- 

 lished the place in nature of the Selachians as the 

 common ancestors of all vertebrate animals from fish 

 up to man. 



None but those who have thoroughly studied the 

 comparative morphology of the vertebrata, who have 

 sought the genetic issue from that labyrinth of intricate 

 morphological problems at the hands of the theory of 

 descent, can duly value the immeasurable service which 

 Gegenbaur has done by this and other " Investigations 

 into the Comparative Anatomy of the Vertebrata." These 

 investigations are as much distinguished by a profound 

 knowledge and careful working out of the wonderfully- 

 extensive empirical materials for the subject, as by their 

 critical acumen and philosophic grasp. At the same 

 time they set in the clearest light the immeasurable 

 value of the theory of descent in the causal explana- 

 tion of the most difficult morphological problems. 

 Gegenbaur might, therefore, with perfect right, enun- 

 ciate this axiom in the Introduction to his " Comparative 

 Anatomy." " The theory of descent will at once find a 

 touchstone of proof in comparative anatomy. Up to 

 this time no experience in comparative anatomy has 



