104 Dr. F. A. Dixey on the j)liytogenetic 



The melanic females would then be instances of reversion 

 or survival, and the whole aspect of the females of the 

 genus would be a case of the well-known rule that in 

 species where sexual dimorphism or " antigeny " occurs, 

 the female most nearly approaches the ancestral type, 

 the male being the more highly specialised form.* The 

 nearest representative of the primitive Argynnis would 

 thus seem to be the female of A. diana, and it is 

 interesting to note that one of the earliest butterflies yet 

 found in a fossiliferous depositf belongs apparently to 

 that species, or at least is not easily to be distinguished 

 from it. The first step in specialisation we may imagine 

 to have been already taken in A. diana by the lightening 

 of the ground colour in certain places, leaving darker 

 patches forming a chain of spots. A further extension 

 of the same process would give us a form like the 

 melanic A. paphia (valesina), or, if a marked accentua- 

 tion of some of the lighter areas took place, the female 

 A. sagana. The bright fulvous ground colour of the 

 majority of Argynnids would then represent a still 

 further advance in specialisation, affecting, as we should 

 expect, chiefly the males ; and in such instances as 



* Scudder (op. cit., vol. 1, p. 533) maintains that in these cases 

 it is the female that departs fi'om the general type, though he 

 admits that this is "precisely the opposite conclusion to that 

 reached by Darwin," He quotes the case of Scmnopsyche 

 (Argtjnnis) diana 5 as an instance of complete departure from 

 the ordinary colouring of the group, but makes no mention of 

 such similar colouring as is visible in A. sagana ? , A. niplie J , 

 A. valesina, &c. The partial dark coloration of certain males 

 he accounts for by saying that "in other cases the melanic feature 

 has been superinduced upon the opposite sex" (vol. 2, p. 951). It 

 does not, however, seem to me that he has given sufficient reasons 

 for his view to ensure its general adoption ; and indeed the following 

 passage would not appear to be in accordance with his own opinion 

 as elsewhere expressed : — " 8ome species, which we can hardly doubt 

 have had a common ancestor, scarcely differ from each other 

 excepting in the character of their antigenic peculiarities, and this 

 accounts for the close resemblance of the females of allied species 

 of Skippers " (lb.). Sm-ely this must mean that the males are the 

 more specialised. A good instance of the preservation of an 

 ancestral character by the female alone is afforded by the spot ^ 

 in P. atalanta 5, as noticed above, p. 93. "With respect to the 

 alleged mimicry on the part of A, diana $ , which forms part of 

 Scudder's argument, see note on pp. 105, 6. 



f " V. pliito" of Heer, from the Oligocene of Eadaboj, Croatia. 

 Vid. Lyell, Elem. GeoL, 1885, pp. 214, 5 ; Edwards, Butterfl. N. 

 Amer., 1879, vol. i. 



