1 6 CER TA IN E VIDENCE OF 



Hence I think I have here produced the most positive 

 analytical evidence of the transformation of species, 

 and of the unity of the derivation of all the species of 

 a given group of animals, that is generally possible. 



Properly, I might spare myself these disquisitions 

 on the question of species, for Yirchow does not go 

 into this main question of the theory of descent but 

 this is very characteristic of his attitude. And just 

 as he nowhere thoroughly discusses the doctrine of 

 transformation, neither does he enter generally on the 

 refutation of any of the other certain proofs of the 

 doctrine of descent which we in fact possess at the 

 present day. Neither the morphological nor the 

 physiological arguments for the theory of descent, 

 neither the rudimentary organs nor the embryonic 

 forms, neither the paleontological nor the chronological 

 argument are anywhere closely examined and tested 

 as to their worth or their worthlessness as " certain 

 proofs." On the contrary, Virchow takes them quite 

 easily, sets them aside, and declares that " certain 

 proofs " of the doctrine of descent do not exist, but 

 remain to be discovered. To be sure, he does not 

 indicate where they are to be sought, nor can he 

 indicate it. How is this strange conduct to be 

 explained ? How is it possible that a distinguished 

 naturalist should resist the most important step for- 

 ward of modern natural science without in any way 



