GENERAL ZOOLOGY 



feed on small aquatic animals, or on plants. After a year or 

 more of this life beneath the surface, during that time under- 

 going many molts, the nymph de- 

 velops rudimentary wings. From 

 the nymph issues a winged form 

 which may be called a subimago. 

 Within a very short time the skin 

 is again cast, even to a thin cover- 

 ing from the wings, and the true 

 imago comes forth. A molt in the 

 winged state is known nowhere 

 else among insects. Though the 

 reduced mouth-parts make it im- 

 possible for the adult May-fly 

 to take any food, the alimen- 

 tary canal is not useless. Air is 



FIG. 14. Nymph and Imago of May-Fly. Natural size 



taken in at the mouth, and the capacious stomach acts as a bal- 

 loon, being provided with valves so that the air cannot escape. 

 Definition of Plectoptera (Gr. plektos* twisted: pteron* 

 wing). The May-flies make up the order Plectop'tera. The 

 Plectoptera may be distinguished from other insects by the 

 reduced mouth-parts, the great disproportion in the size of 



