Animal Morphology. 35 



As the author of the most impressive text -book, 

 Elements of Comparative Anatomy, which has appeared 

 since Huxley's, Prof. Carl Gegenbaur is well Qe enbaur 

 known to all students of zoology. A fellow- 

 student of Haeckel's, he expresses in his work a com- 

 bination of the methods of comparative anatomy and 

 embryology under the dominance of evolutionary ideas. 



Gegenbaur's detailed work is all of importance, but it 

 cannot be summarized here. A single illustration must 

 suffice, concerning a problem with which his name is 

 specially connected the theory of the vertebrate head. 

 This is " the most complex piece of animal architecture 

 with which anatomists have to deal", and there has 

 been a long-standing question as to its structural plan. 

 In 1806, Oken stumbled on the first solution. As he 

 was walking in the Harz Forest, he found the blanched 

 skull of a sheep; he picked it up, and remarked, " It is 

 a vertebral column". This remark was the first expres- 

 sion of his "vertebral theory", which resolved the skull 

 into three parts comparable to vertebrae. This theory 

 was afterwards claimed by Goethe, who may have 

 reached it independently or by unconscious assimilation, 

 and it was afterwards widely accepted and championed 

 by such an authority as Owen. In 1869, Huxley 

 attacked the problem, and showed that the vertebral 

 theory was anatomically fallacious. He showed, for* 

 instance, that when attention was directed to the 

 cranial nerves and the gill-slits, a large number of 

 head-segments were recognizable. Two years later 

 (1871), Gegenbaur took up the subject on a broader 

 embryological basis, and between the two great workers 

 the "vertebral theory of the skull" ceased from troub- 

 ling. Like many another dream of the ' ' Naturphilo- 

 sophie" school, it vanished when brought into touch 

 with facts. Gegenbaur showed that the tenth or vagus 

 nerve, which is distributed to several gill-clefts, must 

 be regarded as composite and corresponds to at least 

 four segments ; that in the lowest (gristly) fishes, where 

 hints of the original vertebrae might be most expected, 

 the skull is an unsegmented gristly brain-box ; and that 

 in higher forms the vertebral nature of the skull cannot 



