ANCESTRY AND CLASSIFICATION. 229 



take ; the principal difference, so far as the 

 wings are concerned, between the early stages 

 of the grasshopper and of the butterfly, is that 

 in the former they are external appendages of 

 the integument, in the latter internal (although 

 morphologically external) ; in the pupal stage 

 they are external in both, and the branching 

 vessels that penetrate them then first assume a 

 definite position, corresponding closely with the 

 direction of the veins which appear in the perfect 

 insects. It is plain that external wing-pads would 

 greatly inconvenience a soft caterpillar, while 

 they are of no disadvantage whatever to the 

 young grasshopper ; and that if the caterpillar 

 state of the butterfly formerly resembled the 

 grasshopper larva, the removal of the wings from 

 the exterior to the interior of the body would be 

 a natural step in the progress of the changes 

 which have culminated in its present condi- 

 tion. 



In the lower insects, like grasshoppers, there 

 are throughout life breathing pores on all the 

 thoracic segments, even on those which bear 

 wings. In the butterfly they are absent from 

 the segments which bear wings, both in the cater- 

 pillar and in the imago. In both these stages, 

 however, as has been stated, these segments bear 

 a distinct tuft of tracheae next to the natural 

 position of a spiracle, which can have no other 



