292 STATES OF INSECTS. (Jmago.) 
most interesting spectacle. At first it was unable to ele- 
vate or even move its wings; but in proportion as the 
aérial or other fluid was forced by the motions of its trunk 
into their nervures, their numerous corrugations and 
folds gradually yielded to the action, till they had gained 
their greatest extent, and the film between all the ner- 
vures became tense. ‘The ocelli, and spots and bars, 
which appeared at first as but germes or rudiments of 
what they were to be, grew with the growing wing, and 
shone forth upon its complete expansion in full magni- 
tude and beauty. 
To understand more clearly the cause of this rapid 
expansion and development of the wings, I have before 
explained to you that these organs, though often exceed- 
ingly thin, are always composed of two membranes, hav- 
ing most commonly a number of hollow vessels, miscalled 
nerves, running between them*. ‘These tubes, which, 
_ after the French Entomologists, I would name nervures, 
contribute as well to the development of the wings, as to 
their subsequent tension. In the pupa, and commonly 
afterwards, the two membranes composing the organs in 
question do not touch each other’s inner surface, as they 
afterwards do: there is consequently a space between 
them ; and being moist, and corrugated into a vast num- 
ber of folds like those of a fan, but transverse as well as 
longitudinal, and so minute as to be imperceptible to the 
naked eye, the wings appear much thicker than in the 
end. Now assoon as the insect is disclosed, a fluid enters 
the tubes, and being impelled into their minutest ramifi- 
cations, necessarily expands their folds; for the neryures 
themselves are folded, and as they gradually extend in 
See above, Vor. II. p. 342—. 
