90 GNATS OR MOSQUITOES — CHAPTER VI 



the antennae of male gnats may serve as chordotonal organs, 

 whereby they are enabled to localise the whereabouts of the 

 female, ordinary hearing may be subserved by these peculiar 

 structures at the base of the halteres. 



Almost the whole of the interior of the thorax is occu- 

 pied with the powerful muscles that actuate the wings, legs, 

 and halteres, but the detailed consideration of their arrange- 

 ment hardly lies within the scope of a work like the present. 



The general structure of the Dipterous leg and wing 

 have already been sufficiently alluded to in the remarks on 

 the terminology of the Order, but as regards their special 

 characteristics in the Culicida;, it may be noted that the 

 former are always proportionally long and slender, and that 

 the hips, or upper sections of the coxae, take the form of 

 obconical processes, immovably connected with the corres- 

 ponding pleurae ; while the trochanters are much smaller^ 

 and take the form of short, globular, or oviform pieces. Of 

 the remaining joints, the femur, tibia, and first tarsal joint 

 are long and linear, and, as a rule, differ but little in length, 

 though their relative proportions furnish valuable specific 

 indications. Not unfrequently the first tarsal is the longest 

 of the three. The remaining four tarsal joints taken together 

 do not, as a rule, equal either of the above linear joints, 

 and generally progressive!}' diminish in length, the last 

 being often scarcely wider than long, and carrying a well- 

 developed epipodium and pulvillus, and a pair of claws, the 

 characters of which have already been sufficiently noticed. 



The third division of the body or abdomen is the longest 

 of the three, but is much more slender than the thorax. It 

 is more or less cylindrical, but depressed, being broader 

 than deep, and is composed of nine segments, none of which 

 are provided with locomotor appendages, although the last, 

 bears a pair of jointed appendages which serve as ex- 

 ternal organs of generation. Each segment is composed 

 of a dorsal and a ventral, rather rigid, chitinous plate, united 

 at the sides by a softer membrane, in which are placed the 

 stigmata or external respiratory apertures. The anterior 

 segments closely resemble each other, except the first, 

 which is a good deal shorter than the rest, and has its 



