Weismannism up to date (1893). 165 



ingenious assumption, the possibility of which I had 

 not foreseen when writing the previous cnapters. 

 The assumption is, that although germ-plasm is 

 universally unstable, the degree of its instability is 

 everywhere restricted within the narrowest possible 

 limits ; so that sexual propagation is still necessary 

 for the purpose of developing congenital variations to 

 the point where they can fall within the range of 

 natural selection,, notwithstanding that they must all 

 have been originated by external causes acting 

 directly on a germ-plasm universally unstable within 

 the narrow limits assumed. But clearly this as- 

 sumption is arbitrary to the last degree, and, no less 

 clearly, it is made by Weismann for the sole purpose 

 of saving as much as he can of his previous theory of 

 variation. His more recent speculations touching 

 the mechanism of heredity are incompatible with his 

 former view of amphimixis as the sole cause of con- 

 genital variations, and therefore he makes this arbitrary 

 assumption for the purpose of representing that am- 

 phimixis may nevertheless still be regarded as 

 a necessary con-caiise. I need not here repeat what 

 has so recently been said touching the sophistry of this 

 assumption in theory, or the demonstrable falsity of it 

 in fact. It is enough to remark, in conclusion, that 

 the game is not worth the candle. It was originally 

 well worth Weismann's while to sustain his funda- 

 mental postulate of the absolute stability of germ- 

 plasm, because he was able to rear upon it his whole 

 theory of evolution. But the only part of this theory 

 which he has now left standing, or which he can now 

 save by his newer postulate of a germ-plasm both stable 

 and unstable at the same time, is his doctrine of 



