THE NERVE-WINGED INSECTS 



97 



FIG. 124. A stone-fly (Pteronarcys regalis}. (Slightly 

 reduced) 



(After Newport, from Folsom) 



larger with each successive molt, until the water nymph sheds its 

 skin for the last time, the gills and mouth-parts are left behind, and 



the winged May- 

 fly comes forth. 

 After flying a 

 short distance it 

 alights and again 

 sheds its skin, a 

 thin layer coming 

 off from all parts 

 of the body, even 

 from the wings, 

 which process 

 must certainly be 

 the " exception 

 which proves the 

 rule, "for no other 

 insects ever molt 

 after becoming winged. The eggs are now deposited by the females 

 either on the surface of the. water or on stones beneath the surface, 

 and in a few hours, or at most in a day or two, 

 the adults die. The nymphs live from one 

 to three years, according to the species, and 

 form an important item of the food of fishes, 

 but are otherwise of no economic importance. 

 The stone-flies (order Plecopterd) l are quite 

 similar to the May-flies in their general hab- 

 its, but quite unlike them in appearance. The 

 hind-wings are much larger than the fore- 

 wings and are folded beneath them in plaits 

 when at rest. The mouth-parts of the adults 

 are of the biting type, but are often poorly 

 developed. The antennae are rather long and 

 slender, and usually there are two many- 

 jointed cerci extending from the tip of the 

 abdomen. The nymphs live beneath stones 

 in swift-running streams and are from one 



1 Yromplecos (plaited), andpteron (wing). (After Comstock) 



FIG. 125. A stone-fly 

 nymph 



