154 PROCEEDINGS OF THE AMERICAN ACADEMY 



side ; but, from the unfortunate want of material, I cannot fairly dis- 

 cuss this point. 



Take, however, another case, which appears to be equally compli- 

 cated, — our native Coppers (Villicaiites). We have one species in 

 which both sexes are fiery red marked with black ; another where both 

 are fulvous marked with black ; others where both sexes are brown ; 

 and several where the male is brown, marked with fulvous, and the 

 female fulvous, marked with brown ; others where the male is wholly 

 brown, and the female fulvous, spotted with brown ; and again others 

 with fiery male, and brown female. We have nearly every possible 

 variation, but the prevalent feature is a dark male, often with more or 

 less metallic reflections, which sometimes increase so as to give the 

 insect a fiery copper hue ; and a fulvous, spotted, and margined female. 

 I do not see how we can po.^sibl}' discover, with any certainty, fi'om 

 within tlie limits of the group of Coppers, what sliould be considered 

 the normal type. Nor are we much better off in an examination out- 

 side the group: there the prevailing tint is either brown or blue; 

 and I am inclined to think that brown, tending strongly to copper, 

 should be considered the normal type ; in which case the males are 

 normal, and the species generally antigenic. 



But sexual dimorphism is not confined to color or pattern ; there is 

 also structural, as well as colorational, antigeny. This term embraces 

 all those minor features which, in these and other animals, have been 

 classed as accessory or secondary sexual peculiarities. Structural 

 antigeny is always complete, and, in direct opposition to the features 

 we have been discussing, is wholly confined to the males. 



In butterflies, structural antigeny is mostly confined to the wings 

 and the legs ; occasionally it appears in the antennfe. Sometimes it 

 affects the contour of the wings. One of the most conspicuous cases 

 among our own butterflies is in Slrymon Titus (Fabr.), where the fore 

 wings of the male have a poinded tip, and the hind wings have the 

 inner angle sharply defined ; while in the female both the tip of the 

 fore wings and the inner angle of the hind wings are broadly 

 rounded. 



Or it may affect the direction of the veins of the wings. Usually 

 the difference between the sexes is slight, and concerns the point of 

 origin of one or two of the upper branches of the subcostal vein of the 

 fore wings ; but occasionally it is very marked, as in many hair-streaks, 

 such as Thecla Edwardsii Saund., where the branches of the sub- 

 costal vein near the end of the cell are thrown far out of place to 

 accommodate a patch of peculiar crowded scales ; this patch itself, 



