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THK AMEBIC AX NATURALIST [Vol. LI 



following the first to which the selectionist ascribes de- 

 ceptive value. Resemblance resulting from undirected 

 variation, or existing for other reasons, is not subject to 

 this criticism. 



Darwin recognized this fact and attempted to throw 

 upon another cause than natural selection a large part of 

 the burden of producing functional resemblance. His 

 idea may best be expressed in his own words : 



The process of imitation probably never commenced between forms 

 widely dissimilar in color. But, starting? with species already some- 

 what like each other, the closest resemblance, if beneficial, could readily 



form was subsequently and gradually modified through any agency, the 

 imitating form would be led along the same track, and thus be altered 

 to almost any extent, so that it might ultimately assume an appearance 

 or coloring wholly unlike that of the other members of the family to 

 which it belonged. There is, however, some difficulty on this head, for 

 it is necessary to suppose in some cases that ancient members belonging 

 to several distinct groups, before they had diverged to the present ex- 

 tent, accidentally resembled a member of another and protected group 

 in sufficient degree to afford some slight protection, this having given 

 the basis for the subsequent acquisition of the most perfect resem- 



Weismann^** attempted to avoid the same difficulty in 

 another way. He makes no assumption that the original 

 difference betwen mimic and model was distinctly less 

 than that appearing at present between typical members 

 of their respective families, but magnifies the importance 

 of the first slight resemblance and subsequent positive 

 variations. He had been deceived repeatedly, at least for 

 the moment, by similarity in the flight of different species 

 whose colors were not the same, and held as a consequence 

 that mere variation in the manner of flight combined with 

 the habit of associating with the form mimicked might 

 have prepared the way for selection. 



Wallace^^ would have it that certain butterflies, having 



40 "Origin of Species/' Chap. XIV. 



50 "The Evolution Theory," Vol. 1, p. 93. London, Edward Arnold, 

 1904. 



