952 TIIIC BUTTERFLIES OF NEW ENGLAND. 



dift'ei- from each otliLT excepting in the character of their antigenic pecu- 

 liarities, and this accounts for the close resemblance of the females of 

 allied species of skippers. Origin through antigeny probably occurs with 

 other animals, but in butterflies it must be unusually common. So, too, 

 witii mimicry. The viceroy and the red-spotted purple are nearly identi- 

 cal in all their earlier stages, and yet utterly diverse in the perfect but- 

 terfly ; both must have sprung from a common source, from which the 

 viceroy has diverged through mimicry in its final stage. 



Some naturalists would doubtless add here as a prime force in the origi- 

 nation of new forms, that presumed sphere of sexual selection which traces 

 to it as a cause all those differences in color and pattern displayed by the 

 two sexes ; for it is a canon of their belief tliat most of the exquisite 

 beauty of the wings of butterflies has arisen, as Darwin has shown 

 good reason to be the case with the brilliant coloring of birds, tlirough 

 sexual selection, the handsomest winning the day. The application, 

 however, of any such theory to butterflies is effectually estopped by the 

 statement of two facts. First, that the latest experimental researches of 

 physiology show that buttei-flies have no power of vision distinct and defi- 

 nite enough to enal)le them to distinguish the delicate patterns on the 

 wiuffs of their consorts, butonlv masses of color. Second, that both col- 

 oriiig and pattern as delicate and as minute as that of tlie winged butterfly 

 is found in very many of their caterpillai's, whose power of vision (through 

 simple and not compound eyes) must be of an immensely inferior grade — 

 probably one that can simply distinguish vaguely the near presence of 

 objects througli tlicir perception of liglit and darkness. 



Allusion has been made above to the differences observable in the male 

 abdominal appendages of some varieties. Now as no two species of but- 

 terfly agree in the structure of these appendages it would appear as if these 

 differences were of exceptional importance and had been given them, as 

 Dufour has remarked, as "the guarantee, the safeguard of legitimate 

 pairing." The differences are sometimes feeble, sometimes extraordinary ; 

 there is every grade between these extremes and the differences are very 

 ^'aried in ch.aracter. Here then especially we have a foundation for that 

 physiological isolation, not absolute but overpowering, which Romanes has 

 80 well urged as one of the principal elements in the origination of species, 

 an isolation which has nearly or quite the same force as geographical se- 

 gregation, of whose influence there is no doubt on any hand. The causes 

 of this variation in these organs we can hardly conjecture; the amouut is 

 immensely greater than the difference in any other structural feature, as 

 may be seen by our plates. Considering how^ closely these parts are con- 

 nected with the generative functions, their importance as a basis for the 

 origination of new forms and as a basis as well in the classification of 

 forms already originated can surelv not be doubted. 



