2 MR. A. R. WALLACE ON THE PAPILIONID.^i 



tion, — a shade of colour, an additional streak or spot, a slight modification of outline con- 

 tinually recurring with the greatest regularity and fixity, while the body and all its 

 other members exhibit no appreciable change. The wings of Butterflies, as Mr. Bates 

 has well put it*, " serve as a tablet on which Natui-e writes the story of the modifications 

 of species ;" they enable us to perceive changes that would otherwise be uncertain and 

 diflB.cult of observation, and exhibit to us on an enlarged scale the effects of the climatal 

 and other physical conditions which influence more or less profoundly the organization 

 of everv living thint?. 



A proof that this greater sensibility to modifying causes is not imaginary may, I think, 

 be drawn from the consideration that while the Lepidoptera as a whole are of all insects 

 the least essentially varied in form, structure, or habits, yet in the number of their specific 

 forms they are not much inferior to those orders which range over a much wader field of 

 nature, and exhibit more deeply seated structural modifications. The Lepidoptera are 

 all vegetable-feeders in their larva-state, and suckers of juices or other liquids in their 

 perfect form. In their most widely separated groups they differ but Little from a com- 

 mon type, and offer comparatively unimportant modifications of structm-e or of habits. 

 The Coleoptera, the Diptera, or the Hymenoptera, on the other hand, present far greater 

 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, carcases, 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 uniform 

 mode of existence ; and the fact that theii* numbers are at all comparable Avith 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 modification. 



The Papilionidae are a family of diurnal Lepidoptera which have hitherto, by almost 

 universal consent, held the first rank in the order ; and though this position has recently 

 been denied them, I cannot altogether acquiesce in the reasoning by which it has been 

 proposed to degrade them to a lower rank. In Mr. Bates's most excellent paper on the 

 Heliconidset, he claims for that family the highest position, chiefly because of the imper- 

 fect 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 Hesperidse and Hetero- 

 cera, which all have perfect legs. Now it is a question whether 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 possession of an organ which in 

 the remainder of the order is altogether wanting. This is, however, the position of the 

 Papilionidfe. The perfect insects possess two characters quite peculiar to them. Mr. 



♦ See 'The Naturalist on the Amazons,' 2nd edit. p. 412. 

 t Transactions of the Linnean Society, vol. xxiii. p. 495. 



