iv VIRCHOW'S SUPPORT 189 



a causa externa as if it was generated outside the organism 

 and introduced from without into it." 



I myself, as might be expected from my general views, 

 have never used the expression internal causes except in the 

 sense of the action of the given constitution of the body, 

 itself partly due to external influences, upon the direction 

 of evolution. 



The supporters of the doctrine of the continuity of the 

 germ-plasm, since they deny the inheritance of characters 

 acquired by the body during life, and admit on the other 

 hand the heredity of those due to influences acting directly 

 on the germ- cells, set up a completely artificial distinction 

 between the nature and the properties of the germ-cells 

 before and after segmentation. Such distinction is not only 

 altogether hypothetical, but completely contradicts that uni- 

 formity which proves the morphological and physiological 

 unity of the living world. 



I have already attempted to demonstrate on other grounds 

 the inconsistency of the supposition of the non-inheritance 

 of acquired characters with that of the unity of the living 

 world. It can also be shown by another consideration that 

 the conception of a fundamental difference between the pro- 

 perties of the germ-cells and of the larva, or of the adult 

 body, must be false, namely, the consideration just indicated, 

 that the germ-cells contain in themselves the material and 

 the properties for the formation of the germ-layers and of all 

 the various cell materials of the adult body ; and that the 

 variety of the latter can only have its ultimate causes in 

 external conditions must therefore be acquired. 



I will not here discuss further the inheritance of acquired 

 morbid conditions, leaving the defence of my views in this 

 point to those special authorities who are on my side, some of 

 whom, like Virchow, have already expressed their support. In 

 particular, with regard to evidence, I may refer to the paper 



