STONE-FLIES, MAY-FLIES, DRAGON-FLIES, ETC. 259 



elongate body, an extremely mobile head, large eyes, incon- 

 spicuous antennae, and four long, rather narrow, stiff, trans- 

 parent, net-veined wings of nearly equal size. Metamorphosis 

 is " incomplete," though the aquatic larva and nymph are a 

 good deal unlike the adult. 



The mouth-parts are well formed for biting. The wings 

 are peculiar in being set back well clear of the legs, and in 

 having a sort of flaw, or nodus, near the middle of the front 

 edge. The legs, as a rule, are short and slender, and are 

 closely fringed or felted with fine spinules ; they are hardly 

 used for progression, the insect being above everything 

 aerial. 



The eggs are laid in or near water in which the larva is 

 hatched. The larva has a most curious hinged, prehensile, 

 and usually elongated labium, known as the mask, which in 



Pio. 118.— Tracheal Gills of Agrionid Larva. 



repose is shut back like a carriage-step and in action shot out 

 like an arm to capture living prey. The typical dragon-fly 

 larva breathes chiefly by the rectum, which is furnished with 

 tracheal papillae, or with distinct tracheal gills : water is 

 inhaled into the rectum, and after use is expelled with 

 sufficient force to propel the animal forwards ; or the rectum 

 with its gills may be rhythmically protruded into the water. 

 In one group of dragon-flies — the Agrionince — the larva has 

 three very large tracheal gills at the end of the abdomen ; 

 these also act as a powerful fin. The larvae are found in the 

 same places as mosquito-larvae, and the actively swimming 

 AgrionincB devour the latter freely. 



The advanced larva, or " nymph," often has a broad, squat 

 abdomen, quite unlike that of the adult. 



Dragon-flies are usually to be seen hawking flies and 

 other insects about ponds and streams, or in damp places. 



