Appendix I. 295 



itself sufficient to cause degeneration, say from 100 to 5, instead 

 of from i oo to 90 or 80, which, for the reasons above given, 

 appeared (and still appears) to me about the most that this 

 principle can accomplish, so long as the original force of heredity 

 continues unimpaired. No doubt we have here what must be 

 regarded as a mere oversight on the part of Professor Weis- 

 mann; but the oversight is rendered remarkable by the fact 

 that he does invoke the aid of reversed selection in order to 

 explain the final disappearance of a rudiment. Yet it is self- 

 evident that the reversal of selection must be much more active 

 during the initial than during the final stages of degeneration, 

 seeing that, ex hypothesi, the greater the degree of reduction- 

 which has been attained the less must be the detriment arising 

 from any useless expenditure of nutrition, &c. 



" And this leads me to a second oversight in Professor Weis- 

 mann's statement, which is of more importance than the first. 

 For the place at which he does invoke the assistance of reversed 

 selection is exactly the place at which reversed selection must 

 necessarily have ceased to act. This place, as already ex- 

 plained, is where an obsolescent organ has become rudimentary, 

 or, as above supposed, reduced to 5 per cent, of its original size ; 

 and the reason why he invokes the aid of reversed selection at 

 this place is in order to save his doctrine of ' the stability of 

 germ-plasm.' That the force of heredity should finally become 

 exhausted if no longer maintained by the presence of selection, 

 is what Darwin's theory of perishable gemmules would lead 

 us to expect, while such a fact would be fatal to Weismann's 

 theory of an imperishable germ-plasm. Therefore he seeks to 

 explain the eventual failure of heredity (which is certainly a fact) 

 by supposing that after the point at which the cessation of selec- 

 tion alone can no longer act (and which his first oversight has 

 placed some 80 per cent, too low), the reversal of selection will 

 begin to act directly against the force of heredity as regards the 

 diminishing organ, until such direct action of reversed selection 

 will have removed the organ altogether. Or, in his own words, 

 ' The complete disappearance of a rudimentary organ can only 

 take place by the operation of natural selection; this principle 

 will lead to its diminution, inasmuch as the disappearing struc- 

 ture takes the place and the nutriment of other useful and im- 



