Systematic Position and Structure 19 



through a single tube on the eighth segment, but by 

 means of a pair of tubes on the back of the thorax. 

 These air pipes are somewhat variable in length and 

 shape and can, in some cases, especially in conjunc- 

 tion with other parts, be depended upon as specific 

 characters. The cephalo-thorax and abdomen are 

 heavily chitinised, the mobility of the latter being 

 due to the soft accommodation membranes between 

 the segments. On the first abdominal segment is 

 a pair of large, thickly branched, circular tufts on 

 short stems. The function of these is apparently to 



Fig. 4. — Pupa of Culex pipiens (greatly enlarged) ; e, eye; 

 a, antennna case; m, mouth parts; /, leg cases; w, wing case; 

 t, thorax; b, breathing tubes; p, paddles; I to IX, abdominal 

 segments. 



