52 CULICID^ [CH. 



In Anopheles the palps are five- jointed and as long as the 

 proboscis in both male and female ; in the female Culex they 

 are very short three- to four-jointed structures, whilst in the 

 male Culex they are five-jointed and at least as long as in 

 Anopheles ; in Aedes the palps are short in both sexes. 



(iii) The second maxillae are united together to form the 

 labium, which ensheaths all the other mouth appendages with 

 the exception of the palps, and the whole structure is generally 

 known as the proboscis. It consists of a soft dorsally-grooved 

 rod which bears a pair of small labellae at the distal extremity. 



Isce. 



sdl. 

 Fig. 26. Transverse section through about the middle of the proboscis of 

 a female A nopheles maculipennis shewing the relative position of the parts 

 when at rest. Two tracheae (tr) and two pairs of extensor and flexor 

 muscles (mus) are seen in the labium. After Nuttall and Shipley. 

 Lettering as in Fig. 27. 



Each of the latter represents the distal segment of the two- 

 jointed second maxillae, the proximal segments of which are 

 completely fused together. The labellae serve to guide the 

 piercing organs of the mosquito. The cavity of the labium is 

 hollow and it is within this space that the embryos of Filaria 

 hancrofti and F. immitis come to rest after leaving the thoracic 

 muscles or Malpighian tubules of an infected mosquito. The 

 labium is covered by a thin cuticle and the filarial escape by 

 rupturing this membrane when the insect feeds. 



In addition to the paired appendages mentioned above, 

 there are two very important median structures. 



(iv) The labrum, or upper lip, which is united with the 

 epipharynx, is an incomplete tube, in cross-section appearing 



