IN BUTTERFLIES 228 



prevailing colors, at least in the temperate zones, 

 are certainly tawny and black or brown ; the 

 latter, marginal. This is the case with the male 

 of the Whirlabout (T. brettus), while the female 

 diverges from the type in becoming wholly brown. 

 In the Tiger Swallow-tail (Jasoniades glaucus), 

 where we sometimes have a black female, it is 

 more difficult to decide what should be considered 

 the normal color, owing to diversity of view upon 

 the relationship of many of the swallow-tails ; but 

 to judge only from those agreed by aU to be most 

 nearly allied to it, there can be no question what- 

 ever that the striped character prevails. 



It will also be noticed, in this last case and 

 others given, that wherever partial antigeny or 

 dimorphism is confined to one sex, it is nearly 

 always to the female ; Cyaniris seems to furnish 

 our only exception to this rule. In these in- 

 stances, on my hypothesis, half of the females 

 depart from the type ; on Darwin's, half of the 

 females, and all of the males. But if, on Darwin's 

 theory, sometimes one half and sometimes three 

 quarters of a species has diverged from the type, 

 why does it so rarely happen that only one fourth 

 of the species diverges ? 



The instances given by Darwin, which strongly 



