NEUKOPTERA. 



417 



when they arrive at the adult state. One species of Perla is 

 very common on the quays of Paris. 



Fig. 386. Perla bicaudata. 



The Epkemerida, or May-fly family, have long, slender bodies, 

 provided with two or three long silky hairs. Their name indi- 

 cates the short duration of their existence. They appear in great 



Fig. 387. Nemoura variegatus. 



Fig. 388. Nemoura variegatus (larva). 



numbers at certain seasons of the year. Their hatching takes 

 place at sunset ; they have coupled and laid their eggs by sun- 

 rise next day, and have ceased to live ; so that the banks of rivers, 

 of ponds, of lakes, are strewed with their bodies. Their number 

 is sometimes so considerable that, according to Reaumur, the soil 

 seems as if it were covered with snow, and they are gathered up 

 for manure. The Common Ephemera, or May-fly (Ephemera 



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