470 MOTIONS OF INSECTS. 
transparent, applied to each other: the upper membrane being very strongly 
attached to the nervures (neure), and the lower adhering more loosely, so 
as to be separable from them. ‘The nervures? are a kind of hollow tube, 
— above elastic, horny, and convex ; and flat and nearly membranaceous 
below,—which take their origin in the trunk, and keep diminishing gradu- 
ally, the marginal ones excepted, to their termination. The vessels contained 
in the nervures consist of a spiral thread, whence they appear to be air- 
vessels communicating with the trachee in the trunk. The expansion of 
the wing at the will of the insect is a problem that can only be solved by 
supposing that a subtile fluid is introduced into these vessels?, which seem 
perfectly analogous to those in the wings of birds, and that thus an impulse 
is communicated to every patt of the organ sufficient to keep it in proper 
tension. We see by this, that a wing is supported in its flight like a sail 
by its cordage.$ It is remarkable that those insects which keep the longest 
on the wing, the dragon-flies (Libellulina) for instance, have their wings 
most coyered with nervures. The wings of insects in flying, like those of 
other flying animals, you are to observe, move vertically, or up and down, 
In considering the flight of insects, I shall treat of that of each order 
separately, beginning with the Coleoptera or beetles. Their subsidiary in- 
struments of flight are their wing-cases (e/yra), and in one instance winglets 
(alulz). The former, which in'some are of a hard horny substance, and in 
others are softer and more like leather, though they are kept'immoveable in 
flight, are probably, by their resistance to the air, not without their use on 
this occasion. The winglets are small concavo-conyex scales, of a stiff 
membranaceous substance, generally fringed at their extremity. I know at 
present of only one coleopterous insect that has them (Dytiscus marginalis), 
They are placed under the elytra at their base. Their use is unknown; 
but it may probably be connected with their flight. The wings of beetles 
are usually very ample, often of a substance between parchment and 
membrane. The neryures that traverse and extend them, though not 
numerous, are stronger and larger than those in the wings of insects of the 
other orders, and are so dispersed as to give perfect tension to the organ. 
When at rest—except in Molorchus, Atractocerus, Necydalis, and some 
other genera— they are folded transversely under the elytra, generally near 
the middle, with a lateral longitudinal fold, but occasionally near the ex- 
tremity. When they prepare for flight, their antenne being set out, the 
elytra are opened so as to form an angle with the body and admit the free 
play of the wings; and they then fly off, striking the air by the vertical 
motion of these organs, the elytra all the while remaining immoyeable. 
The Cetonie, however, as noticed by M. Audouin, differ from most if not 
all other coleopterous insects in keeping their elytra closed during their 
flight.4 During their flight the bodies of insects of this order, as far as I 
have observed them, are always in a position nearly vertical, which gives 
to the larger sorts, the stag-beetle for instance, a very singular appearance. 
Olivier, probably having some of the larger and heavier beetles in his eye, 
1 French naturalists use this term (nervure) for the veins of wings, leaves, &., re- 
stricting nerve (nerf) to the ramifications from the brain and spinal marrow. 8 
have adopted the term, which we express in Latin by neura, from the Greeks vee 
2 Recent observations by several distinguished microscopical naturalists fully con 
firm this opinion. 
5 Jurine, Hymenopt. 19. 
4 Ann. Soc, Ent. de France, viii. p. xviii. 
