1890 ON WEISMANN'S THEOEY 225 



To E. B. Poulton, Esq. 



Geanies, Boss- shire : November 2, 1889. 



My dear Poulton, Continuing our antipodal cor- 

 respondence, and taking the points in your last letter 

 seriatim, I quite saw that your theory of repair was 

 ' the logical outcome of Weismann's ' (being, in fact, a 

 direct application of his views on phytogeny to the 

 case of repair) ; but I did not know whether the out- 

 come had been traced by him or by yourself. Now, I 

 understand, I may allude to it as yours. Again, what 

 I meant about regeneration of entire limbs, &c., was 

 that, to meet such cases, your diagram would require 

 modification in the way that you now suggest. Has 

 it occurred to you as an argument in favour of this 

 suggestion (i.e. that the ' potentiality ' of somatic 

 germ-plasm may in such cases be arrested in its pro- 

 cess of ontogeiietic diffusion), that Darwin has shown, 

 or at least alleged, that all such cases may be traced 

 to special adaptation to special needs, dangers, &c. 

 so that the arrest may have been brought about in 

 these cases by natural selection ? 



If you deem the ' chief difference ' between Dar- 

 win's and Weismann's theory of heredity to be ' that 

 the one implies material particles and the other only 

 physical and chemical constitution,' then, it seems to 

 me, Weismann's theory will become identical with 

 Herbert Spencer's seeing that this is virtually the 

 only respect in which Spencer's differs from Darwin's. 

 But I think there is another and a much more 

 important respect in which W.'s theory differs from 



