SOME AQUATIC INSECTS 91 



and soon bursts, permitting a fresh air supply 

 to be drawn in. 



When the perfect insect is about to emerge, 

 the nymph brings its body along the surface of 

 the water so that the back of the thorax is well 

 exposed ; the skin dries and cracks, and then the 

 perfect insect emerges, gradually extricating its 

 legs, heads, wings, and body from the close-fitting 

 nymphal sheaths. The empty nymph-skin now 

 floats upon the surface of the water, forming a 

 kind of raft, upon which the freshly emerged 

 Gnat rests while its wings expand and dry, and 

 its body and legs harden. This is quickly 

 accomplished on a fine summer day, and the 

 perfect Gnat then rises on its delicate outspread 

 wings and flies away. In windy weather, how- 

 ever, when the surface of the pool is broken into 

 ripples, the final transformation is fraught with 

 considerable danger, and thousands of emerging 

 Gnats are drowned. 



The so-called Phantom Larva, the larva of 

 Corethra, frequents still pools that are shaded by 

 overhanging trees. It is two-thirds of an inch 

 long, and has a wonderfully transparent body. 

 This transparent body, coupled with the insect's 

 habit of remaining absolutely motionless in the 

 water for a long time, makes it by no means easy 

 to detect, and it is this that has -gained for the 

 Corethra its popular name of Phantom Larva. 

 It attacks and devours the smaller larvae of 

 Gnats and Mayflies, and also the tiny crustaceans 

 Daphnia and Cypris. Save for the beautiful fan 

 composed of a row of feathered bristles on the 

 under surface of the end of its body, used for 



