472 MOTIONS OF IXSECTS. 



Orylhlalpa, 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 of 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 domcsticvs) fly with an undulating 

 motion, like a woodpecker, alternately ascending with expanded wings, and 

 descending with folded ones.^ The field and mole-crickets {Gryllns cam- 

 pestris and Grt/l/ofalpa 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. 



Hemiplerous 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 diflferent substances ; the first being generally 

 corneous, and the latter membranaceous. The former or homopterous 

 division includes the Cicadarks Latr., Aphis, Ckermes, Thrips, and Coccus ; — 

 and the latter the heteropterous division, comprehending, besides the 

 Geocoriscs Latr,, Notonecta, Sigara, Kepa, Ranatra, and Naucoris of 

 Fabricius. The posterior tibiae of some of this last division {Li/gccus 

 pliyllopus, foUaceus, &c. F.) are furnishfd 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 

 aerial 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 invent 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 Trichoptera 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 longituiiinally. Some of these flies, 

 I have 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 antennae 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 appentlciges 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 Gcer* {Loboplwru 

 hexaptcrd), as having six wings; for, besides the four ordinary ones, it has 

 a winglet (alula) 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 know, are covered with scales of various shapes. Their ner- 



1 Hist. Ins. G3. 2 Nat. Hist. ii. 82. 



^ I have separated this tribe from the rest under the name of Petahpus 

 K. i\Is. 

 4 Lesser, 1. i. 100, note*. De Geer, ii. 460. t. ix. f. 9. 



