ILLUSTRATIVE OF NATURAL SELECTION, 133 
hi 
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 
species - population would be only equal to that of 
sections of the other orders having a similar uniform 
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 sus- 
ceptible of specific modification. 
Question of the rank of the Papilionide. 
The Papilionide are a family of diurnal Lepidop- 
tera 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 Heliconide, 
(published in the Transactions of the Linnean So- 
ciety, vol. xxiii, p. 495) 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 Hes- 
peride and Heterocera, which all have perfect legs. 
Now it is a question whether any amount of differ- 
ence which is exhibited merely in the imperfection 
or abortion of certain organs, can establish in the 
