234 1NSECTA. 



covered with small scales, which at the first glance resemble 

 dust, and give them the magnificent colours in which they 

 are drest. 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 gra- 

 dually and in series, like tiles on a roof. Before the superior 

 wings of these Insects are two species of epaulettes ptery- 

 goda 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 tbey are dis- 

 tant^). Directly under them, in the Diptera, are two small 

 movable threads with a claviform termination, which, accord- 

 ing to the general opinion(2) seem to replace the two wings 

 that are wanting. They are called (balanciers) halteres. 

 Other two-winged and more extraordinary Insects have also 

 two halteres, but situated at the anterior extremity of the 

 thorax, which to distinguish from the others we will call pro- 

 halteres. 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, 



(1) The Insect is supposed to be at rest. The rapid vibration of these organs 

 appears to us to be one of the principal causes of the humming produced by these 

 animals. The explanations hitherto given of it are not satisfactory. 



(2) They are, in my opinion, appendages of the tracheae of the first abdominal 

 segment, and correspond to that space, perforated with a small hole, adjacent to 

 the anterior side of an opening, with a membranous and internal diaphragm, that 

 is seen on each side in the same segment in everal species of Acrydium. See 

 my Mem. sur les Append. Artie, des Insect., in the Mem. du Mus. d'Hist. Nat. 



