STRUCTURE OF INSECTS. 13 



the Lepidoptera are clotlied with exceedingly minute feather-scales, 

 which are rubbed ofF at the slightest touch, and which are somewhat 

 analogous to the scales of fishes. In the Trichoptera and some Diptera 

 the wings are more or less clothed with hairs. In the Diptera there is a 

 pair of slender clubbed organs attached at the sides of the metathorax 

 termed halteres, and which have been considered as representing the 

 hind wings, whilst in the Strepsiptera a somewhat similar pair of 

 twisted organs are placed at the side of the thorax, in front of the 

 wings : these have been termed pseudo-halteres, and are the analogues 

 of the fore-wings. In addition to the foregoing appendages, the pro- 

 thorax is occasionally armed with a pair of moveable spines (imibones 

 K. and S.), and in the Lepidoptera there is a pair of scales {jpatagia 

 K. and S.) clothed with hair, distinct from the tegula?, with which 

 they are confounded by Burmeister (^Manual, p. 77.). The latter 

 organs acquire a large size in the Lepidoptera, and are the pieces clothed 

 with hair, which repose upon the base of the wings. The Diptera are 

 also furnished with a small membranous appendage [alula) attached 

 to the posterior base of the wing, which Kirby and Spence regard as 

 the true analogue of the posterior pair of wings: they are, however, 

 decidedly portions of the fore wings ; there exists a similar pair of 

 winglets at the internal base of the elytra of the Dyticidae, and which 

 I have discovered equally developed in Hydrous piceus. 



The Legs, or organs of terrestrial or aquatic progression, are six in 

 number, attached in pairs to the three thoracic segments: they are arti- 

 culated with the sternum of each segment, and are composed of a series 

 of articulations, united together in such a manner as to permit the re- 

 quired movements ; thus when the insect is pre-eminently cursorial, the 

 basal articulations are freer than in those species which being nata- 

 torial, the movement is confined to a simple working forwards and 

 backwards of the leg. In other species, which arc saltatorial, the hind 

 legs are elongated and thickened, for the purpose of giving support 

 to the strong muscles by which leaping is performed ; in other species, 

 which are raptatorial, the forelegs are formed into a prehensile organ, 

 whilst, in the fossorial species, the same legs are altered, so as to serve 

 for burrowing or scratching in the sand. The chief divisions of the legs 

 are the coxa, trochanter, femur, tibia, and tarsus : the coxa is the gener- 

 ally large and flattened piece which articulates with the sternum, of a 

 variable form, and which assumes its maximum degree of development 

 in Dyticus and Ilaliplus : the trochanter is a small piece connecting the 



