VIII 



MAY-FLIES 



307 



narrow leaflets, traversed 

 by central tracheae, and 

 fringed along the fore edge 

 by close-set filaments. 



" Polymitarcys is the 

 commonest species in the 

 neighbourhood of Paris, 

 and the one best worth 

 study. The winged fly ap- 

 pears for three or four days 

 in succession in most years, 

 and affords a curious spec- 

 tacle. On coming out of 

 doors in a morning, \ve see 

 the pavement strewn all 

 over with pretty flies rather 

 like Butterflies. Sometimes 

 they lie so thick as to hide 

 the pavement completely, 

 and this sight is repeated 

 three or four days running. 

 Our surprise is increased 

 when \ve learn that these 

 Insects issue from the 

 rivers, in which they pass 

 their early stages. It is 

 hard to imagine that so 

 many can come forth from 

 the water at the same time 

 -all the more because on 

 searching the river one 

 might fail to find a single 



FIG. 92. -Larva of Polymitarcys 

 virgo, X 6. From Vayssiere. The 

 tracheal gills of the left side are 

 displayed. 



X 2 



