2 MR. A. R. WALLACE ON THE PAPILIONIDÆ 
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 Nature writes the story of the modifications 
of species ;" they enable us to perceive changes that would otherwise be uncertain and 
difficult 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 every living thing. 
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 wider 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 structure 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, aquatie, 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 faet 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 modification. 
The Papilionidæ 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 
Heliconidzet, 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 Hesperidæ and Hetero- 
v ms ee have perfect legs. Now it is à question whether any amount of difference 
z eu A 1s -— u. in = imperfection or abortion of certain organs, can establish 
as vd — € c B to a - grade of organization ; still less can this be 
exhibits modifications vena io it ia en . — — - vestre 
the remainder of the order is alto eth ei Be ii ides aute — 
ilot. Mets Hs er wanting. This is, however, the position of the 
possess two characters quite peculiar to them. Mr. 
* See ‘The Naturalist on the Amazons,’ 2nd edit. p. 412. 
+ Transactions of the Linnean Society, 
paper on the 
vol. xxiii. p. 495. 
