IV EARLIER AND LATER VIEWS OF WEISMANN 129 



phism of butterflies has its causes in great part in the differ- 

 ences in physical constitution of the sexes. It is quite 

 another matter in the case of those sexual characters which, 

 like the voice of male grasshoppers, have an undoubted im- 

 portance in the relations of the sexes. These can certainly 

 with greater probability be derived from sexual selection." 



Eegretting as I do that my views are so much in opposi- 

 tion to those of Weismann, it is some consolation to me that 

 this opposition essentially applies only to his new views, not 

 to his old, which latter in very important points agree with 

 mine. From the quotation just given this is sufficiently 

 evident, and I myself could not find better cases in support 

 of my views than those there brought forward ; nor could 1 

 more distinctly oppose the excessive estimation of sexual 

 selection than Weismann formerly did when criticising 

 Darwin. And yet Darwin attributed to that process an 

 importance but very slight in comparison to the omnipotence 

 with which Weismann to-day endows it, notwithstanding 

 that the experiments desired by Weismann in the above 

 passage are yet to be made. The great agreement between 

 many propositions of Weismann's earlier theories and my 

 view strikes me now most forcibly as I read his treatise 

 again for the purpose of this discussion of the question 

 of the effect of climate on the modification of forms. In tlie 

 sixth section of this treatise, under the heading of general 

 conclusions, Weismann even makes the statement that differ- 

 ences of specific value can arise entirely through the influence 

 of external conditions of life. He believes that species- 

 formation, at least in Lepidoptera, has taken place to a large 

 extent in this way, and among them more than other animals, 

 because the conspicuous colours and markings of the wings 

 and body are without biological importance, that is, are of no 

 use for the preservation of the individual, and therefore of the 

 species, and thus they cannot have come under the operation 



