SOME AQUATIC INSECTS 89 



throughout the entire length of the body, 

 carrying a supply of air to every part. The 

 terminal segment of the abdomen, which is 

 beyond the origin of the tail-tube, is fringed with 

 bristles and terminated by five slender conical 

 plates. 



If a glass jar is carefully dipped in a stag- 

 nant pool so as to capture a number of these 

 Gnat larvae, their movement may be conveni- 

 ently watched. At first there is a great excite- 

 ment amongst the little creatures at their sudden 

 removal from the pool, and the larvae will be 

 seen swimming about in all directions by curious 

 wriggling movements of their bodies. In a very 

 short time, however, they will calm down and 

 assume their normal positions and movements. 

 They will then be seen to rise and rest in such 

 a position that the tip of the curious respiratory 

 syphon is flush with the surface of the water. 

 While hanging thus head downwards, the body 

 of the Culex larva sways gently backwards and 

 forwards as the insect sweeps the food into its 

 mouth by means of the mouth-bristles. If we 

 examine the tip of the respiratory tube under 

 the microscope, we shall be able to see that it is 

 provided with five flaps, which can be opened or 

 closed at pleasure, and which when opened form 

 a minute kind of cup which prevents the surface 

 film of water entering the air-tube. When the 

 larva wishes to descend towards the bottom of 

 the pool, these flaps are tightly closed, so that 

 the air within the respiratory tube cannot escape, 

 When the larva once more rises to the surface, 

 the pointed tips of these flaps meet the surface- 



