INSECTA. 345 



all sorts of locomotive organs, wings and feet, which, in several, act 

 asfns. 



The wings are membranous, dry, elastic organs, usually diapha- 

 nous, and attached to the sides of the back of the thorax: the first, 

 when there are four, or when they are unique, on those of its second 

 segment, and the second on those of the following or of the meta- 

 thorax. They are composed of two membranes laid one on the 

 other, and are traversed in various directions by more or less nu- 

 merous nervures, which are so many tracheal tubes, now forming a 

 net-work, and then simple veins. The Libellulag, Apes, Vespae, 

 Papiliones, &c., have four wings; but those of the latter are co- 

 vered with small scales, which at the first glance resemble dust, and 

 give them the magnificent colours in which they are dressed. They 

 are easily removed with the finger, and that portion of the wing be- 

 comes transparent. By the aid of glasses we discover that these 

 scales are of various figures, and implanted in the wing by means of 

 a pedicle, arranged gradually and in series, like tiles on a roof. 

 Before the superior wings of these Insects are two species of epau- 

 lettes pterygoda which extend posteriorly along a portion of the 

 back on which they are laid. The wings of some Insects remain 

 straight, or are doubled transversely. Those of others are folded 

 or plaited longitudinally like a fan. Sometimes they are horizontal, 

 and sometimes inclined in the manner of a roof; in several they cross 

 on the back, and in others they are distant. Directly under them, 

 in the Diptera, are two small movable threads with a claviform ter- 

 mination, which, according to the general opinion, seem to replace 

 the two wings that are wanting. They are called halteres. Other 

 two-winged and more extraordinary Insects have also two halteres, 

 but situated at the anterior extremity of the thorax, which to distin- 

 guish from the others we will call prohalteres. Above these ap- 

 pendages is a little membranous scale formed of two pieces united 

 by one of their edges and resembling a bivalve shell it is the alula 

 or cueilleron. The same appendage is also observed under the ely- 

 tra (at their base) of some aquatic Coleoptera. 



Many Insects, such as the Melolonthae, Cantharides, &c., in lieu 

 of the two superior or anterior wings, are furnished with two species 

 of scales, more or less solid and opaque, which open and close, and 

 beneath which, when at rest, the wings are transversely folded. 

 These scales or wing cases are called elytra. The Insects provided 



2 T 



