326 INSECTA. 



are four, or when they are unique, on those "of its second segment, and 

 the second on those of the following or of the metathorax. They are 

 composed of two membranes laid one on the other, and are traversed in 

 various directions by more or less numerous nervures, which are so many 

 tracheal tubes, now forming a net-work, and then simple veins. The 

 Libellulse, Apes, Vespse, Papiliones, &c., have four wings ; but those 

 of the latter are covered 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 becomes 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. Be- 

 fore the superior wings of these Insects are two species of epaulettes 

 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 longi- 

 tudinally 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 moveable threads with a claviform termination, which, accord- 

 ing to the general opinion, seem to replace the two wings that are 

 wanting. They are called halleres. Other two-winged and more ex- 

 traordinary Insects have also two halteres, but situated at the anterior 

 extremity of the thorax, which to distinguish from the others we will 

 call prohalteres. Above these appendages 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 elytra (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 with them are 

 named Coleoptera, and in such they are never absent, though this is 

 sometimes the case with respect to the wings. In other Insects the 

 extremity of the scale is completely membranous, or like the wing : 

 they are styled Hemiptera. 



The scutel or scutellum is usually a small triangular piece, situated 

 on the back of the mesothorax, and between the insertions of the elytra 

 or of the wings. Sometimes it is very large, and then it covers the 



