150 PROCEEDINGS OF THE AMERICAN ACADEMY 



XIII. 



ANTIGENY, OR SEXUAL DIMORPHISM IN BUT- 

 • TERFLIES. 



By Samuel H. Scudder. 



Presented, March 14, 1877. 



In bis work on Selection in relation to sex, Darwin discusses the dif- 

 ference of coloring which frequently distingui.shes the sexes of butter- 

 flies, and concludes that "the male, as a general rule, is the most 

 beautiful, and departs most from the usual type of coloring of the 

 group to which the species belongs." (op. cit. i. 390.) Of the first 

 proposition there can be no doubt; but, in the second, two distinct 

 elements appear to be confounded : the separation of these is the 

 object of the present eommunicalion. 



Sexual dimorphism, or antigeny,* as exhibited in butterflies, is of 

 two kinds, — colorational and structural. Colorational antigeny again 

 may be divided into two classes: the first including those cases in 

 which it is partial ; the second, those in which it is complete. 



As one example of partial antigeny, we may take Ci/aniris pseudar- 

 giolus (Boisd.-LeC). In the south, a portion of the females of the 

 spring brood have the upper surface of the wings uniformly brown ; 

 another portion have the greater part blue, like the male ; in the north, 

 all the females are blue. In Jasoniades Turnus (Linn.), the males, and 

 in the north all the females, are yellow above, heavily banded with 

 black ; in the south, a large proportion of the fem;des have lost the 

 yellow ground, and become wholly black ;, while others retain the 

 universal ground-tint of the male. The dark female of Atrytone 

 Zahuloa (Boisd.-LeC.) was for a long while considered a species dis- 

 tinct from the normal female, in which the tawny colors of the male 

 are shared by its mate. 



* This term, signifying opposition or rlivcrsity of the sexes, is proposed to 

 avoid circumlocution; for tliere are so ni;iny forms of sexual dimorphism 

 requiring specific names, that a compound term for the general phenomenon 

 becomes inconvenient. 



