No. 506] DAL'WIX AM) MUTATION THEORY 71 



we have no evidence of the appearance, or at least of the continued 

 procreation under nature, of abrupt modifications of structure; and 

 various general reasons could he assigned against such belief. 



I am not aware that Mr. Darwin ever presented definite 

 and convincing reasons for the sharp demarkation here 

 attempted and, indeed, I can not see how the state of 

 knowledge in his time could have justified it, for, as I 

 have already stated, mutations had not been much looked 

 for among feral plants and animals. In fact, by abso- 

 lutely excluding from his theory the idea that mutation 

 could occur under nature, Mr. Darwin, by the force of 

 his great authority and influence, would have prevented 

 a careful weighing of the pros and cons, if the human 

 mind had at that time been prepared to weigh them. It 

 is practically only since the Darwinian hypotheses have 

 themselves been subjected to prolonged scrutiny, and 

 since De Vries and a few others entered upon detailed 

 experimental examination of this particular subject, 

 within the last twenty years, that the matter can be said 

 to have received anything like scientific treatment. 



But, after all, Darwin was not wholly prejudiced 

 against a belief in the occurrence of mutations in nature, 

 for he several times expressed the opinion that the estab- 

 lishment of such a fact would in some ways be an ad- 

 vantage to the evolution theory. For instance, m a 

 letter of August, 1860, to W. H. Harvey, he says : 



This of course refers to discontinuous 

 organisms under natural conditions, for he 

 found evidence to make him believe in simi 

 among domesticated animals and plants. 

 Darwin never specified the directions in ^ 

 in mutation would be a help to him, but, 

 remarks made in various places, I fancy ht 



] think Mr 



