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, and covered 
with moisture, but this speedily evaporates, the or- 
gans become firm, and 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 ner- 
vures, which are tubular vessels ramifying through 
the whole extent of the wing, and which are them- 
Belves 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 with 
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 
