54 CULICID^ [CH. 



4-6 times as large as the abdomen. The major portion is 

 taken up by the mesothorax, which forms the chief region of 

 the mid-body. Its dorsal element, the scutum, is a large 

 plate projecting slightly over the head ; posteriorly it is 

 bounded by a curved narrow thickening of the integument 

 known as the scutellum, which often bears conspicuous rows 

 of hairs. Behind this comes the post-scutellum, or metathorax, 

 a triangular plate which overlaps part of the first abdominal 

 segment. The presence or absence of hairs and scales on the 

 post-scutellum is of generic importance. 



At each side of the thorax are two large spiracles, respec- 

 tively pro- and meso-thoracic in origin (Fig. 4). 



The six legs are each composed of the typical insect parts, viz. 

 the coxa, trochanter, femur, tibia and tarsus, the last of which 

 is five-jointed and ends in a pair of claws. The four proximal 

 joints are often covered with scales. The first joint of the 

 tarsus is long and hairy and its proportionate length with the 

 tibia is of specific value. The shape of the claws varies accord- 

 ing to the sex ; in the female they are equal and simple or 

 may have a single tooth ; in the male those of the fore-legs 

 are usually unequal and toothed. 



The wings are long and narrow and while at rest lie flat 

 over the abdomen. The venation is very characteristic, there 

 being six distinct longitudinal veins and two prominent fork- 

 cells, and the costal vein extends completely round the edge 

 of the wing (Fig. 28). 



The auxiliary vein is distinct, sometimes extending beyond 

 the middle of the wing. The second, fourth, and fifth longi- 

 tudinal veins are furcate. 



The hind margin of the wings is fringed with a row of hairs 

 or scales and in addition all the veins are more or less covered 

 with scales. The shape and arrangement of these scales varies 

 in different groups and is the chief basis of Theobald's classi- 

 fication. 



On the under surface, at the base of the wing, is a curious 

 stridulating organ, consisting of a complex system of chitinous 

 bars, by means of which two ridged surfaces are made to rub 

 against each other when the wings vibrate (Fig. 28). It is 



