INTRODUCTION. 85 



is feeble and languid, and usually fixes itself on the 

 exuviae from which it has just emerged, or on some 

 neighbouring object, till it acquire some degree of 

 strength. All the parts are soft at first, arid covered 

 with moisture, but this speedily evaporates, the or- 

 gans become firm, arid every symptom of debility 

 soon disappears. In this process, the development 

 of the wings is not the least interesting object. Hi- 

 therto compressed within a very narrow space, they 

 at first appear as small crumpled packets, affording 

 no indication of the extension and beauty which they 

 ultimately acquire. But their folds and corrugations 

 soon begin to give way to the pressure of the rier- 

 vures, which are tubular vessels ramifying through 

 the whole extent of the wing, and which are them- 

 selves excited and dilated by having an aqueous fluid 

 impelled into them from the trunk of the insect. 

 As the nervures diverge, the interjacent spaces gra- 

 dually become tense, the animal assisting greatly in 

 extricating the folds, by frequently shaking its wings 

 with a tremulous motion. The spots and other 

 markings are by degrees unfolded, and after the ex- 

 panded wings have been for a short time exposed to 

 the sun, the new-born fly launches into the air witb 

 as much apparent ease and confidence as if it had 

 been long familiar with such an exercise. 



The appearance of these creatures in their various 

 states of caterpillar, pupa, and butterfly, is so strik- 

 ingly dissimilar, that it was long a general belief that 

 they underwent, at each successive stage, a complete 



