OF BUTTERFLIES 259 



of that vigor in the breeding season. This theory, 

 too, would at most hardly do more than explain 

 the differences one now finds between the two 

 sexes, and could not take into account, except 

 in a very secondary way, by transmission, that 

 wonderful variety and brilliancy of color found 

 throughout whole groups of butterflies and com- 

 mon to both sexes. 



Wallace has pointed out that, in general, color 

 is proportionate to integumentary development, 

 that no insects have such widely expanded wings 

 in proportion to their bodies as butterflies and 

 moths, that in none do the wings vary so much in 

 size and form, and in none are they clothed with 

 such a beautiful coating of scales. In support of 

 the physical theory of the production of color, he 

 maintains that numerous color changes must have 

 developed in such long continued expansion of 

 the membrane, — color changes which have been 

 checked, fixed, utilized, or intensified, according to 

 the needs of the animal, by natural selection ; and 

 by this alone would he explain all the variety 

 which we find in the whole tribe of butterflies. 

 And this indeed seems to be the best explanation 

 that can be offered, and one that is in better ac- 

 cordance with our knowledge of the distribution of 



