ILLUSTRATIVE OF NATURAL SELECTION. 133 



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 Papilionidce. 



The Papilionidas 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 Heliconida3, 

 (published in the Transactions of the Linnasan 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- 

 peridge 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 



