472 MOTIONS OF INSECTS. 
Gryllotalpa, the right is laid over the left. The wings in this order, though 
always ample and larger than the tegmina, do not invariably form a 
quadrant pf a circle, falling often short of it. They are extended by means 
of nervures, which, like so many rays, diverge from the base of the wing; 
and are intersected alternately by transverse ones, which thus form qua- 
drangular areas, arranged like bricks in a wall. When at rest, they are 
longitudinally folded. The flight of these insects, as far as it has been ob- 
served, much resembles, it is said, that of certain birds. Ray tells us that 
both sexes of the house-cricket (Gryllus domesticus) fly with an undulating 
motion, like a woodpecker, alternately ascending with expanded wings, and 
descending with folded ones. The field and mole-crickets (Gryllus cam- 
pestris and Gryllotalpa vulgaris), as we learn from Mr. White*,—and, 
since the structure of their wings is similar, probably the other Orthoptera, 
—fly in the same way. 
Hemipterous insects, with respect to their hemelytra, may be divided into 
two classes. Those in which they are all of the same substance —vary- 
ing from membrane to a leathery or horny crust —and those in which the 
base and the apex are of different substances ; the first being generally 
corneous, and the latter membranaceous. The former or homopterous 
division includes the Cicadarie Latr., Aphis, Chermes, Thrips, and Coceus ;— 
and the latter the heteropterous division, comprehending, besides the 
Geocorise Latr., Notonecta, Sigara, Nepa, Ranatra, and Naucoris of 
Fabricius. The posterior tibie of some of this last division (Lygeus 
phyllopus, foliaceus, &c. F,) are furnished on each side with a foliaceous 
process—which may act the part of outriggers, and assist them in their 
flight. I can give you no particular information with respect to the 
aérial movements of the insects of this order: the British species that 
belong to it are generally so minute that it is not easy to trace them with 
the naked eye ; and unless some kind optician, which is much to be 
wished, would inyent a telescope by which the proceedings of insects 
could be examined at a distance, there is no other way of studying them. 
The four wings of the next order, the Zrichoptera or case-worm flies, 
both in their shape and nervures resemble those of many moths; only 
instead of scales they are usually covered with hairs, and the under wings, 
which are larger than the upper, fold longitudinally. Some of these flies, 
I haye observed, move in a direct line, with their legs set out, which makes 
them look as if they were walking in the air. In flying they often apply 
their antennz to each other, stretching them out straight, and thus pro- 
bably are assisted in their motion. ; 
The Lepidoptera vary so infinitely in the shape, comparative magnitude, 
and appendages of their wings, that I should detain you too long did I 
enlarge upon so multifarious a subject. I shall therefore only observe, 
that one species is described, both by Lyonet and De Geer* (Lobophora 
hexaptera), as haying six wings; for, besides the four ordinary ones, it has 
a winglet (a/ula) attached to the base of the lower one, and placed, when 
the wings are folded, between it and the upper. These organs in this 
order, you knew, are coyered with scales of various shapes. Their ner- 
1 Hist. Ins. 63. 2 Nat. Hist. ii. 82. 
oe have separated this tribe from the rest under the name of Petalopus 
. Ms. 
4 Lesser, I. i, 109, note*. De Geer, ii. 460, t. ix. f. 9. 
