CHAPTER X. 



DIVERSITY OF THE SEXES IN COLORING AND STRUCTURE. 



ANTIGENY, signifying opposition or antagonism 

 of the sexes, is a term applied to what might also 

 be called sexual dimorphism, and embraces all 

 forms of secondary sexual diversity, some of 

 which will now be considered. 



The partial form of sexual dimorphism, referred 

 to at the close of the last chapter, or an antigeny 

 affecting only a portion of one sex, is by no 

 means rare among butterflies, but it always 

 assumes one of two aspects, albinism or melan- 

 ism ; in each of these it may become univer- 

 sal and therefore complete. In high temperate 

 regions albinic antigeny finds its most complete 

 expression ; toward the tropics melanic antigeny 

 prevails ; and in accord with this general state- 

 ment we may observe that in the butterfly whose 

 history was last given it is in the southern part 

 of its range that melanic antigeny makes its ap- 

 pearance, that is, a part of the normally blue 

 males become brown. 



Another instance of partial melanic antigeny 

 may be seen in our Tiger Swallow-tail [Fig. 153], 



