CABBAGE WHITE BUTTERFLIES 173 



There are great differences between Insects as to 

 the amount of structural change which goes on during 

 the pupal stage. In some (Blow-fly, etc.) the whole 

 larval body is at this time reconstructed ; in others 

 (Moths, Butterflies) the new parts, fashioned during 

 the larval stage, are completed internally during the 

 pupal stage ; while in a third case (Chironomus, etc.) 

 most of the new parts are already complete, inside 

 and out, when pupation sets in, and require little more 

 than to be hardened, or in the case of certain organs to 

 be exercised a little, before they enter into full activity. 



It is likely that primitive Insects never acquired 

 wings, and led much the same life during the adult, 

 reproductive stage as before. There are still some 

 few Insects (Spring-tails, Silver-fishes) of which this 

 is true. But it is common for adult Insects to fly. 

 Flight gives facilities for finding a mate not too 

 closely related, and for laying eggs in likely places, 

 which would be inaccessible to an animal which could 

 only crawl or run. Flight does not of necessity bring 

 about any change of food. If there is no change of 

 food, there is no absolute need of a resting-stage. 

 The Dragon-fly feeds upon live Insects, as it did in 

 its earlier aquatic condition ; it has no resting stage 

 at all. But the flying adult is likely to profit by a 

 change of food. The larva, as a rule, is voracious ; it 

 needs a capacious stomach and stout jaws, but no 

 extraordinary nimbleness or quickness of perception. 

 When the Insect comes to take long excursions in 

 the air, it will in general require a lighter and more 

 nutritious food, such as the nectar of flowers. Change 

 of food naturally brings about changes in the mouth- 



