24 THE WINGS OF INSECTS. 



terpillar,'^ and he has given aplatef wherein is dehneated 

 the body of the embryo butterfly with its wings, legs, 

 &;c. apparent after the larva-skin had been removed : 

 these winos, as in the chrysalis state, are much smaller 

 than when the insect has arrived at perfection ; very 

 often they are not a tenth part of the size which they 

 subsequently acquire. 



The wings of all insects consist of two membranes, 

 generally transparent, applied to each other ; the upper 

 one is very strongly attached to the nervures which 

 ramify over the wing : these nervures are hollow, elas- 

 tic, and of a homy consistence when the insect has 

 arrived at perfection, but they are soft and capable of 

 dilatation immediately after the insect emerges from its 

 chrysalis case ; in consequence of this softness the 

 insect is able to distend them by forcibly injecting them 

 with fluid, the membranes are extended at the same 

 time, and the wing is made to assume its final size ; 

 this distention is effected as soon as the insect casts off 

 its pupa covering, it sometimes occupies but a few 

 minutes, and at other times requires more than an 

 hour, but after this first enlargement the wings under- 

 go no further increase, and remain of the size then 

 acquired during the life of the insect. It may be ob- 

 served that the wings only become enlarged at the time 

 alluded to, the other parts of the insect are of their full 

 size, and do not increase during its subsequent life. 



The nervures are thick and strong in the wings of 

 insects having large bodies and making rapid flights, 

 the hawk moths for instance ; and those that keep 

 longest on the wing, dragon flies, have their wings al- 

 most covered with nervures ; these nervures are plain- 

 ly visible when the wings are naked, and if the wing of 

 a butterfly have the scales, — or apparent dust, — with 

 which it is covered, removed, the nervures then become 

 distinctly visible, these scales may be removed by the 

 careful friction of a wet hair pencil, and on examining 



*Swam. Bib. Nat. P. IT. p. 14. fSwam. Bib. Nat. Tab. XXI. 



