No. 605] 



ANIMAL COLORATION 



275 



fluence to induce uniformity of coloration seems dis- 

 credited. 



If the possibility of the direct influence of local climatic 

 factors be excluded, Piepers' hypothesis, that mimicry is 

 largely due to species having independently attained the 

 same stage of development orthogenetically, leaves the 

 facts of geographical distribution of mimics and their 

 models enshrouded in mystery. That this is a very real 

 difficulty follows from Punnett's statement,^' 



Exaniplos of oloso repem])]ance between butterflies which live in dif- 

 ferent i^arts of the world are relatively rare and serve to emphasize the 

 fact that the great bulk of tliese resemblance cnses arc associated in 

 pairs or little groups. 



Finally, instances of mimicry are, after all, only scUvted 

 exaini)les of resemblance, and it is desirable, if jHis.-ilile, to 

 formulate an explanation that will ap])ly to all e(|ually 

 well. But whether the likeness between them rise? by 

 sporting or otherwise, it is not to be supposed that Phas- 

 mids and green leaves or dry twigs possess Mendelian 

 factors in common. Therefore it seems profitable to pro- 

 ceed for a little upon the assnm]>tion that mimicry is in 

 some cases at least a vi-ible token of the fact that the 

 species manifesting it arc linked by some bond other than 

 common descent, common habit, or ex]iosnre to the influ- 

 ence of a common environment. AVhnt tlii< may ho. does 

 not appear, unless through mutual i-csciuhlauco a<l van- 

 tage accrues to some or all of the forms concerned. 



Evidence compiled by Marshall"^ shows that birds un- 

 doubtedly attack butterflies, but others deny that they 

 feed upon the insects freely enough to afifect the evolu- 

 tion of their coloration, and more particularly the mimetic 

 resemblances between different species. Hence there 

 IS plainly a question at issue concerning the sufficiency of 

 an assigned cause to produce a stated effect. Under the 

 circumstances any (n ldence tending to show that the fre- 

 quency of birds' attack^ ]ia^ b(vn nndoresf imated. or that 



