"* * * The organic growth of butterflies is primarily 

 conditioned by climatic influences. * * * The proof is to 

 be found in the facts revealed by the geographical distri- 

 bution of butterflies, by the variations corresponding 

 to the seasons, and by experiments regarding the influence 

 of artificial heat and cold on development." 



Experimental proof is naturally of vital importance for 

 Elmer's theory. He cites in this regard especially the ex- 

 periments of Merrifield, Handfuss, Fischer, Fickert, and 

 Countess Maria von Linden. In Eimer's own laboratory 

 the latter performed experiments on Papilionides, "which 

 prove in the most striking manner the recapitulation of the 

 family-history in the individual." "The fact that it is pos- 

 sible by raising or lowering the temperature during the 

 time of development to breed butterflies, possessed of the 

 characteristics of related varieties and species living in 

 southern and northern regions respectively, characteristics 

 not merely of color and design, but also of structure, is 

 complete irrefragable proof of my views." 



Eimer therefore belongs to the class of naturalists, like 

 Wigand, Askenasy, Naegeli, and many others, who reject 

 the purely mechanical trend of Darwinism and recognize 

 an "immanent principle of development." He seeks the 

 essential cause of evolution in the constitution of the plasm 

 of organisms. This very analogy between the devel- 

 opment of the family and that of the individual should, in 

 fact, convince any one of this. If Eimer chooses to refer 

 the analogy to "growth" and to designate the evolution of 



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