86 THE GENETIC AND 



I must here be permitted to take Yirchow exactly 

 at his word. I endorse almost all that he has said in 

 these and the following sentences. The only difference 

 in our views is this, that Yirchow regards the theory 

 of descent as an unproved and unproveable hypothesis ; 

 I, on the contrary, as a fully established and indispen- 

 sable theory. How then will it be if the teachers of 

 whom Yirchow speaks agree with my views, if apart, 

 of course, from all special theories of descent they, 

 like me, consider the general theory of descent as the 

 indispensable basis of all biological teaching ? And 

 that that is actually the case Yirchow may easily 

 convince himself if he looks over the recent literature 

 of zoology and botany ! Our whole morphological 

 literature in particular is already so deeply and com- 

 pletely penetrated by the doctrine of descent, phylo- 

 genetic principles already prevail so universally as a 

 certain and indispensable instrument of inquiry, that 

 no man for the future would deprive himself of their 

 help. As Oscar Schmidt justly observes " Perhaps 

 ninety-nine per cent, of all living, or rather of all work- 

 ing zoologists, are convinced by inductive methods of 

 the truth of the doctrine of descent." And Yirchow 

 with his magisterial requirements will attain only the 

 very reverse of what he aims at. How often has it 

 not been said already that science must either have 

 perfect freedom or else none at all ? This is as true 



