114 Darwin, and after Darwin. 



form that they presented. I do not think it was just in 

 Weismann to remark. ' if Wagner had confined himself 

 to the statement that geographical isolation materi- 

 ally assists the process of natural selection, and 

 thus also promotes the origination of new species, he 

 would have met with little or no opposition ; but then, 

 of course, in saying this much, he would not have 

 been saying anything new." No doubt, as I have 

 just shown, he ought thus (as well as in other and 

 still more important respects not perceived by Prof. 

 Weismann) to have limited his statement ; but, had 

 he done so, it does not follow that he would not have 

 been saying anything new. For, in point of fact, in 

 as far as he said what was true, he did say a great 

 deal that was also new. Thus, most of what he said 

 of the principle of separation (apogamy) was as new 

 as it was true, although, as we have seen, he said it 

 to very little purpose on account of his identifying 

 this principle as a whole with that of but one of its 

 forms. Again, notwithstanding this great error, or 

 oversight, he certainly showed of the particular form 

 in question — viz. geographical isolation — that it was 

 of considerably more importance than had previously 

 been acknowledged. And this was so far a valuable 

 contribution to the general theory of descent. 



Prof. Wei.smann's essay, to which allusion has just 

 been made \ was, however, in all respects a great 

 advance upon those of Wagner. It was not only 

 more comprehensive in its view of the whole subject 

 of geographical isolation, but likewise much more 

 adequate in its general treatment thereof. Its prin- 



> Ueber den Einfuss der holirting auf die Artbildung (1872). 



