294 STATES OF INsEcTS. (Jmago.) 
great importance to produce the expansion of the wing. 
And Jurine found that every nervure contains a trachea, 
which, proceeding from the interior of the trunk in a 
serpentine direction, follows all the ramification of the 
nervure, though it does not fill it®. Though Reaumur 
attributes the expansion of the wings chiefly to an aque- 
ous fluid, yet he suspects that the azr on some occasions 
contributed to it * 
The wings of the other tribes of insects probably differ 
from the Lepidoptera in the manner in which they are 
folded. It should seem from Reaumur’s description, that 
those of some flies, instead of the straight transverse folds 
of the former, have angular or zigzag folds¢; which 
equally shorten the wing. Many Hymenoptera have 
wings without any nervures except the marginal. We 
may conjecture that these are more simply folded, so as 
to render their expansion more easy; but even in these 
wings there are often tracheze, which appear as spurious 
nervures, and help to effect the purpose we are consi- 
dering. 
The operation of expanding their wings, in by far the 
larger number of insects, takes place gradually as de- 
2 Swamm. Bibl. Nat. i. 184. > Jurine Hymenopt- 16. 
© iy. 342. Herold also attributes the rapid expansion of the wing 
to the flow of an aqueous fluid, which he calls dood, into the ner- 
vures, the orifices of which open into the breast. Entwickelungs. 
der Schmetterl. 101. sect. 106.—M. Chabrier, in hisadmirable Essai 
sur le Vol des Insectes (Mém. du Mus. 4ieme, ann. 325), having ob- 
served a fluidin the interior of the nervures of the wings of insects, 
thinks it probable that they can introduce it into them and withdraw 
it at their pleasure : the object of which, he conjectures, is either to 
strengthen them and facilitate their unfolding, or to vary the centre 
of gravity in flight, and increase the intensity cf the centrifugal force. 
¢ Ibid. 340. 
