INSECTS 



threadlike and provided with comparatively few short 

 hairs (A). The sexes differ also in the mouth parts, for, 

 as in the horseflies, the males lack mandibles. 



The mouth parts of the mosquito, in the natural posi- 

 tion, do not appear as separate pieces, as do those of the 

 horsefly. The various elements, except the palpi, are com- 

 pressed into a beak that projects forward and downward 

 from the lower part of the head (Fig. 176 A, Prb). The 

 length of the beak varies in different kinds of mosquitoes; 

 it is particularly long in the large South American species 

 shown in Figure 176. 



When the beak of the female mosquito is dissected 

 (Fig. 176 B), the same equipment of parts is revealed as is 

 possessed by the female horsefly (Fig. 169 B), namely, a 

 labrum (Lm), two mandibles (\ld), two maxillae (Mx), a 

 hypopharynx (Hphv), and a labium (Lb). It is the labium 

 that forms most of the visible part of the beak, the other 

 pieces being concealed within a deep groove in its upper 

 surface. 



The labrum (Pig. 176 B, Lm) is a long median blade, 

 concave below, terminating in a hard, sharp point; it is 

 probably the principal piercing tool of the mosquito's 

 outfit. The mandibles of the mosquito (Md) are very 

 slender, delicate bristles; those of the species figured are 

 so weak that it would seem they can be of little use to the 

 insect. The maxillae (Mx) are thin, flat organs with 

 thickened bases, each terminating in a sharp point armed 

 on its outer edge with a row of backward-pointing, saw- 

 like teeth which probably serve to keep the mouth 

 parts fixed in the puncture as the piercing labrum is 

 thrust deeper into the flesh. The palpi (MxPlp) arise 

 from the bases of the maxillae. The hypopharynx (Hphv) 

 is a slender blade with a median rib which is traversed by 

 the channel of the salivary duct. Its upper surface is con- 

 cave and, in the natural position, is closed against the 

 concave lower side of the labrum, the two apposed pieces 

 thus forming between them a tube which leads up to the 



[336] 



