72 EFFECTS OF ADAPTA TION sec. 



EURTHER COXSIDERATIONS ON THE ADAPTATION AND DIREC- 

 TION OF Evolution of the Markings of Cater- 

 pillars. Absence of Sexual Combination in this 

 Evolution 



I much resjret that Weismann's views and mine with reojard 

 to the causes of evolution are now so divergent, after the 

 great agreement between us, which I felt myself entitled to 

 assume in my publication on the variation of the wall-lizard, 

 judging from Weismann's researches on the markings of the 

 SphingidaB caterpillars, which demonstrate definite directions 

 in the modifications of these markings. 



I was rejoiced to be able to appeal to the fact that the re- 

 sults of these researches of Weismann admitted of an explana- 

 tion in accordance with my views, and thought I had good 

 grounds, therefore, for believing that we agreed. I was the 

 more pleased at this supposed harmony because I had 

 arrived at my results quite independently of Weismann's 

 paper. 



Weismann was one of the first who insisted that variation 

 takes place in constant directions ; he also recognised the 

 truth that simply from the fact of the given constitution of 

 the body it could not occur in any direction at random. 

 Eormerly, moreover, he did not allow such exclusive dominion 

 to adaptation as now. Thus he says in his work on season- 

 dimorphism : ^ " Little as I am inclined to talk of an unknown 

 transmutation force, I w^ould as emphatically insist here again 

 that the modification of a species depends only in part on ex- 

 ternal conditions, and in the other part on the specific consti- 

 tution of the species." 



^ a. Weismann, Stiidien zur Descendenz-Theorie. 1. Ueber den Saison Di- 

 moiyhismus der Schmetterlinge, Leipzig, Engelraann, 1875. 



