Aquatic Insects 95 



the sides of the body. Many aquatic 

 insects, however, have all the spiracles 

 closed with the exception of one pair at 

 the head end and one pair at the apex of 

 the abdomen. More commonly, only the 

 terminal abdominal spiracles are func- 

 tionable. This adaptation of the breath- 

 ing apparatus obtains in most of the 

 mature aquatic insects and in some of 

 the larvae. Other kinds of aquatic larvae 

 have no functionable spiracles, but are 

 provided in their stead with a varying 

 number of lateral or terminal processes 

 known as tracheal gills. Many of the 

 adult aquatic insects obtain their supply 

 of oxygen direct from the air by rising 

 to the surface of the water and bringing 

 the tip of the abdomen into contact with 

 the air. Various methods are employed 

 to retain on some part of their body a 

 supply of air so that some time may pass 

 before it is necessary for the insect to 

 rise again to the surface. 



