Phenomena of Variation and Geographical Didribution. 163 



or of liabits. The Coleoptcra, the Diptera, or the H3-iiienoptera, on 

 the other hand, prei^ent ftxr greatei- and more essential variations. In 

 either of these orders we have both vegetable and animal feeders, 

 aquatic, and terrestrial, and parasitic groups. Whole families are 

 devoted to special departments in the economy of nature. Seeds, 

 fruits, bones, carcasses, excrement, bark, have each their special and 

 dependent insect tribes from among them ; whereas the Lepidoptera 

 are, with but few exceptions, confined to the one function of devouring 

 the foliage of living vegetation. We might, therefore, anticipate that 

 their population would be only equal to those of the sections of the 

 other orders that have a similar iniiform mode of existence ; and the 

 fact that their numbers are at all comparable with those of entire 

 orders, so much more varied in organization and habits, is, I think, a 

 proof that they are in general highly susceptible of specific modifi- 

 cation. 



The Papilionidaj are a family of diurnal Lepidoptera which liave 

 hitherto, by almost universal consent, held the fii'st rank in the order ; 

 and though this position has recently been denied them, I can not 

 altogether acquiesce in the reasoning by which it has been proposed 

 to degrade them to a lower rank. In Mr. Bates' most excellent paper 

 on the Helicouidse, he claims for that family the highest position, 

 chiefly because of the imperfect structure of the fore legs, which is 

 there carried to an extreme degree of abortion, and thus removes 

 them further than any other family from the He.speridre and Hetero- 

 cera, which all have pei'fect legs. Isow it is a question Avhether any 

 amount of difference which is exhibited merely in the imperfection or 

 abortion of certain organs, can establish in the group exhibiting it a 

 claim to a high grade of organization ; still less can this be allowed 

 when another group, along with perfection of structure in the same 

 organs, exhibits modifications peculiar to it, together with the posses- 

 sion of an organ which in the remainder of the order is altogether 

 wanting. This is, however, the position of the Papilionida;. Tlie 

 perfect insect possess two characters quite peculiar to them. jNIr. 

 Edward Doubleday, in his " Genera of Diurnal Lepidoptera," says : 

 "The Papilionidse may be known by the apparently four-branched 

 median nervule and the spur on the anterior tibite, characters found 

 in no other family." The four-branched median nervule is a character 

 so constant, so peculiar, and so well marked, as to enable a person to 

 tell, at a glance at the wings only of a butterfly, whether it does or 

 does not belong to this family ; and I am not aware that any other 

 gioup of buttei-flies, at all comparable to this in extent and modifica- 

 tions of form, possesses a characrer in its neuration to which the same 



