MOUTH PARTS : MOSQUITO 29 



faintly pigmented hairs, on each side of the canal. The distal border of 

 the hypopharynx is split up into a row of innumerable elongate processes, 

 which give it the appearance of a frayed piece of cloth. In Ceratopogon 

 (figs. 1 and 2) both organs have indented margins, with five processes 

 produced distally between the notches ; the labrum-epipharynx is the 

 broader organ of the two, so that its processes overlap those of the 

 hypopharynx. 



In Phlebotomus the two parts of the food canal are more pointed at 

 their distal ends. The borders of both are split up into fine tooth-like 

 processes, those on the hypopharynx being much smaller and more 

 numerous than those on the epipharynx. The significance of these 

 ' teeth ' will be discussed when the parts in the mosquito have been 

 described. 



In each of the above flies the two sucking chambers are well devel- 

 oped and functional. In Simulium the buccal cavity is like that of 

 Tabanus, while the pharynx is composed of three plates, like that of the 

 mosquito. The two are, as in Tabanus, placed perpendicular to one 

 another. In Ceratopogon the buccal cavity is also composed of two 

 plates, dorsal and ventral, but it is smaller, and does not appear to take 

 as much part in the sucking operation as the pharynx ; this is also 

 composed of two plates, and resembles the buccal cavity, to which it is 

 inclined at about half a right angle. In Phlebotomus the buccal cavity, 

 which resembles that of the others, is small ; the pharynx is the more 

 important sucking chamber, and is composed of three chitinous plates. 



The mosquito represents an extreme type, characterized by great 

 elongation of the mouth parts, reduction in the size of the buccal cavity, 

 and a corresponding increase in the size of the 



pharynx. The elongation of the mouth parts is accom- The Mos fl uit 



Plate VII 

 panied by a reduction in the transverse diameter, 



specially noticeable in the labium. 



In the Anopheline mosquitoes the proboscis is held straight in front of 

 the head in the position of rest, while in the other genera it is inclined 

 downwards. The position in which it is held in the act of feeding is, 

 however, the same in the two forms, namely, perpendicular to the long 

 axis of the body, or nearly so. 



The mandibles (figs. 1 and 3) are extremely slender slips of chitin, armed 

 only at their distal ends. In sections the blade appears concave on its 

 inner surface, and is closely pressed against the hypopharynx. At the 

 tip, in the case of Anopheles, the blade is broadened out a little, and has a 

 short row of extremely fine serrations. In many species of Culex the 



