THE 



AMERICAN NATURALIST 



THE INHERITANCE OF POLYMORPHISM AND 

 SEX IN COLIAS PHILODICE 1 



JOHN H. GEROULD 



There is perhaps no phenomenon of greater general 

 interest to students of organic evolution than polymor- 

 phism, yet, although it is of frequent occurrence in 

 insects, in few cases has it been investigated with long 

 continued and thorough experiments in breeding. Ento- 

 mologists have usually been content to prove that dif- 

 ferent forms arise from the eggs of a single female, or 

 of similar females of the same species, without reference 

 to the male parent or to the immediate ancestors of the 

 female. The time has come when these interesting phe- 

 nomena, lying at the very doors of those at least who live 

 in the country, demand more serious attention than they 

 have yet received. 



Colias philodice, the common yellow butterfly of the 

 clover, called sometimes the clouded sulphur or roadside 

 butterfly, is distinctly dimorphic in the female sex, in 

 that the ground color of the wings is either yellow or 

 white, the yellow female in most localities being much 

 the more abundant. As this common species can readily 

 he bred in large numbers, it affords excellent material 

 for studying the inheritance of dimorphism limited to 

 one sex. 



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