416 THE INSECT WORLD. 
when they arrive at the adult state. One species of Perla is very 
common on the quays of Paris. 


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Fig. 386.—Perla bicaudata. 
The Ephemeride, or May-F ly 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 

x 
Fig. 387.—Nemoura variegata. Fig. 588.—Nemoura variegata (larva). 
numbers at certain seasons of the year. Their hatching takes 
place at sunset; they have coupled and laid their eggs by sunrise 
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 Réaumur, the soil 
seems as if it were covered with snow, and they are gathered up 
for manure. The Common Ephemera, or May-Fly (Ephemera 
