218 [Marcli, 



wanting ; the second compartment of the hind wing, or median band, 

 is o£ a somewhat darker brown colour ; the third compartment or 

 discal band is bluish ash colour, and the eyes therein are rather more 

 distinct, and the hind wings are less rounded in form. 



These two forms of E. Medea are probably well known to almost 

 all lepidopterists, but one of my reasons for calling attention to their 

 occurrence is, that they were referred to by Mr. Wailes as " varieties^'' 

 and although one form doubtless is a "variety " of the other, in the 

 sense in which a naturalist like Mr. Darwin uses that term ; yet it is not, 

 in my view, a variety, in the sense in which that word is commonly used 

 by collectors of Lepidoptera. I would submit that the word variety 

 should be reserved for abnormal specimens of any species of either 

 ^ex ; such as those caused by disease, or by the larva having fed on an 

 unusual food-plant, or by having been subjected to unusual climatal con- 

 ditions, orliy any other cause not operating constantly and regularly 

 in the production of any second form, and that it should not be 

 applied to a diverging form which constantly occurs, is confined to 

 one sex, and is probably a species in the course of formation. 



Instead of speaking of these two forms as varieties, I think it 

 would probably be more correct to regard them as instances of sexual 

 dimorphism. 



Assuming that Ave regard them as such, the question naturally 

 arises as to which of them is the oldest or the type ? Mr. Scudder 

 says,* " that in all cases of colorational antigeny, it is the female, and 

 " never the male, which first departs from the normal type of colouring 

 "of the group to which the species belongs." 



My experience of E. Medea certainly leads me to agree with Mr. 

 Scudder, so far as that species is concerned, and I consider that 

 one of the two forms of the female of this species which most nearly 

 approaches the male in appearance, that is, the form in which the 

 discal band is bluish ash colour, is to be regarded as the type (female); 

 and that the other form, in which the discal band is ochreous-brown 

 or whitish-ochreous, is the diverging form. If this opinion be correct, 

 then this species {Erehia Medea) forms an exception to the rule, 

 according to Mr. Darwin, who observes :t " AVhen the sexes of butter- 

 " flies differ, the male, as a general rule, is the more beautiful, and 

 " departs more from the usual type of colouring of the group to 

 " which the species belongs. Hence, in most groups the females of 

 "several species I'csemble each other much more closely than do 

 " the males." 



* Proceedings of the American Academy of Arts and Sciences. Vol. xii, 1877, p. 152. 

 + The Descent of Man, and selection in relation to set. 2nd edit., 1875, p. 310. 



