64 CULICID^ [CH. 



provided with strong mandibles adapted for biting. The shape 

 of the head varies in different famihes, being long and narrow 

 in the majority of Anophelinae and large and broad in the 

 Culicinae. The thorax is broad and its three segments are 

 fused together to form a single mass. The abdomen is long 

 and slender, and is composed of nine distinct segments. The 

 anus opens at the apex of the terminal segment and is sur- 

 rounded by four, more or less well-developed, tracheal gills. 

 The respiratory system consists of two main longitudinal 

 tracheae opening on the dorsal surface of the eighth abdominal 

 segment, either by two separate apertures in a hollow at the 

 base of a papilla (as in the Anophelinae) or at the apex of a 

 distinct breathing tube or syphon of varying length (as in the 

 Culicinae). The presence or absence of this structure furnishes 

 an easy method of distinguishing the larvae of Anophelines from 

 those of the Culicines. 



Moreover, it is possible to distinguish different genera and 

 even species by means of the larval characters, such as the 

 arrangements of the hairs on the segments, the form of the 

 mandibles and other head appendages, the shape of the 

 syphon, etc. 



The larva progresses in the water by means of energetic 

 wriggling movements, but the larvae of Culicines are generally 

 more active than those of the Anophelines. Moreover, in the 

 latter, because of the situation of the respiratory apertures, 

 and the presence of the palmate hairs, the larvae float hori- 

 zontally under the surface of the water, and closely resemble 

 bits of floating sticks. The Culicine larvae merely bring the 

 tip of the breathing syphon in contact with the surface film 

 of the water and then hang downwards so that their bodies 

 make an angle with the surface of the water. This position 

 is also partly due to the heavy jaws and head, which weigh 

 down the anterior end. The difference in the attitude assumed 

 by the larvae when at the surface of the water is very 

 characteristic and constitutes one of the simplest methods of 

 distinguishing between Anophelines and Culicines at this stage 

 of development (Fig. 30). 



The larvae may be either herbivorous or carnivorous. As a 



