28 THE EVOLUTION OF MAN. 



of Amphibian is an actual parent-form of the higher Ver- 

 tebrates and of Man. On the contrary, this important 

 assertion must be clearly understood to mean, that the living 

 forms, which have been mentioned, are side branches, which 

 are much more nearly allied, and similar to the extinct 

 common parent-forms, than any other known animal forms. 

 In their internal characteristic structure they remain so 

 similar to the unknown parent-forms, that we should class 

 them both in one order, if we had the latter before us in 

 a living state. But the direct descendants of the primitive 

 forms have never remained unmodified. Hence it is 

 quite impossible that among the living species of animals 

 we should find the actual ancestors of the human race in 

 their characteristic specific forms. The essential and charac- 

 teristic features, which more or less closely connect living 

 forms with the extinct common parent-forms, are to be 

 found in the internal structure of the body, not in the 

 external specific form. The latter has been much modified 

 by adaptation. The former has been more or less retained 

 by heredit}^. 



Comparative Anatomy and Ontogeny indisputably prove 

 that Man is a true Vertebrate, so that the special genealo- 

 gical line of Man must of course be connected with that of 

 all those Vertebrates which are descended from the same 

 common root. Moreover, on many definite grounds, sup- 

 plied by Comparative Anatomy and Ontogeny, we must 

 assume only one common origin for all Vertebrates — 

 a monophyletic descent. Indeed, if the theory of descent 

 is correct, all Vertebrates, Man included, can only have 

 descended from a single common parent-form — from a single 

 primitive Vertebrate species. The genealogical line of the 

 Vertebrates, therefore, is also that of Man. 



