66 An Examination of Weismannism. 



external influences which affect them are intimately connected 

 with the state of the organism in which they lie hid. If it be 

 well nourished, the germ-cells will have abundant nutriment; 

 and, conversely, if it be weak and sickly, the germ-cells will be 

 arrested in their growth. It is even possible that the effects of 

 these influences may be more specialized ; that is to say, they 

 may act only upon certain parts of the germ-cells. But this is 

 indeed very different from believing that the changes of the 

 organism which result from external stimuli can be transmitted 

 to the germ-ceils, and will re-develop in the next generation at 

 the same time as that at which they arose in the parent, and in 

 the same part of the organism 1 . 



It will be perceived that Weismann himself here 

 very clearly draws all the distinctions between cases 

 i, 2, and 3, as above explained. Therefore it 

 becomes the more remarkable that he should not 

 have perceived how radically inconsistent it is in him 

 thus to entertain as "possible" congenital variations 

 belonging to the case 2. For, as we have now so 

 fully seen, the theory of germ-plasm (as distinguished 

 from that of stirp) cannot entertain the possibility of 

 an hereditary and specialized change of any kind as 

 thus produced by external conditions of life : should 

 such a possibility be entertained, there must obviously 

 be an end to the absolute stability of germ-plasm, 

 and a consequent collapse of Weismann's theory of 

 evolution. Either germ-plasm is absolutely stable, 

 or else it is but highly stable. If it is absolutely 

 stable, individual variations of an hereditary kind can 

 occur only as results of sexual admixtures of germ- 

 plasm, and Weismann's theory of evolution is 

 established. But if germ-plasm is not absolutely 

 stable (no matter in how high a degree it may be so) 



1 Essays, <&c, 2nd ed., p. 105. 



