740 



CLASS IV. INSECTA. 



backward. In the male the mandibles are absent and the hypo- 

 pharynx has fused with the labium. 



The head is joined to the thorax by an unusually flexible neck. 



The segments of the thorax are 

 much fused and their limits dim- 

 cult to make out. The wings are 

 membranous and, except in Culi- 

 cidae (Fig. 473), devoid of scales ; 

 the " cells " are never numerous 

 (Fig. 366). Very frequently at 

 the posterior side of the base of 

 the wing a notch separates a 

 small lobe, the alula, from the 

 rest of the wing ; and still nearer 

 the base one or even two more 

 lobes may be seen called the 

 squama (or antitegula) and tegula. 

 These afford facilities for the 

 which in 



FIG. 472. Bad of labium, labrum and 

 epipharynx, mandibles and first 

 maxilla of Anopheles maculipennis, 

 magnified (after Nuttall and Shipley). 

 1 labium ; 2 labrum and epi- 

 pharynx ; 3 first maxilla ; 4 man- 

 dible ; 5 labellae. 



folding back of the wing, 

 repose lies almost always flat and un- 

 crumpled on the abdomen. The hal- 

 teres are small knobbed structures 

 which like the wings can vibrate 

 rapidly. They are apparently sensory 

 in function and in some cases possibly 

 stridulating. The legs are slender, 

 usually hairy. The tarsus has almost 

 always five segments, and terminates 

 in two well-developed claws, under each 

 of which is a free pad, the pulvillus ; 

 a median empodium may also be pre- 

 sent between the claws. 



The abdomen may show as many as 

 nine segments (Fig. 365) or as few as four. 

 In the latter case a certain number of 

 segments are withdrawn posteriorly 

 into those in front and the first segment 

 is concealed by the thorax. An ovipositor may be present. 



In those Diptera which suck juices a powerful sucking pharynx, 

 which expands under muscular effort, is found, also certain sacs 



FIG. 473. Scales on the edge of 

 the wings of Anopheles maculi - 

 pennis, magnified (after Nuttall 

 and Shipley). 



