1914.] NATURAL SCIENCES OF PHILADELPHIA. 1G9- 



such resemblance. I doubt whether Dr. Skinner would venture to- 

 apply the same argument to the polymorphic mimetic females of 

 the Ethiopian Papilio dardanus or to many other examples that 

 could be cited. The North American females are not nearly so 

 striking as these, but their patterns are explained by the theories of 

 mimicr,y and by no other theories as yet suggested. 



There are doubtless certain general principles which underlie the 

 whole phenomenon of sexual dimorphism. One of these is obvious — 

 the linking of color, pattern and structure (as we see in the shape 

 of the wings or in the forefeet of so many butterflies) with sex — • 

 a linking which is so apt to occur in insects as well as in several other 

 groups, and is so specially conspicuous in the Lepidoptera Rhopalo- 

 cera. To this principle I think another may be added, at any rate 

 so far as the butterflies are concerned — the greater variabilit}' of 

 sex-limited patterns in the female (33) . But these general principles 

 do not explain the different categories of antigenetic females, although 

 they may, and I think do, explain the fact that there is material out 

 of which these categories have been built by selection. They would 

 also, of course, account for any antigenetic characters, if such there 

 be, that have not been subject to selection. They are the nearest 

 approach to a general law governing antigeny as a whole that can be 

 offered in the present state of our knowledge. 



Beyond these principles we have, I submit, to look for special 

 explanations rather than for general laws. 



(1) The mimetic females are probably to be explained, as Wallace 

 suggested (2, p. 22), by the special needs and special habits of the 

 sex, but also by the fact that the difference in pattern variability 

 may be such that the evolution of mimicry is initiated in one sex 

 and prevented in the other (33, p. 132). 



(2) A second class of female patterns is procryptic, meeting the 

 special needs of the sex by promoting concealment. 



(3) In a third class the whole or a certain proportion of the females 

 of a species retains ancestral patterns (or structures like the fore 

 feet mentioned above) which have been lost or become more degener- 

 ate in the males. 



(4) Finally the fact that males ai*e so often distinguished from their 

 females by brilliantTtints which are pigmentary in some species and 

 structural in others and by scent-producing organs of many kinds 

 strongly suggests an important fourth class due to the operation of 

 sexual selection. 



The summary briefly set forth in the last paragraphs will, I think,. 



