LIFE-HISTORY OF ^MAY-FLIES 233 



accumulate by diffusion. Such larva; are very common 

 in ponds and slowly moving streams. A second kind 

 of larva is one adapted to live in the rapid streams of 

 upland districts. The body and its appendages are 

 broad and flattened, enabling these species to with- 

 stand or evade the current by clinging to stones 

 whilst utilising it for respiration. These larvae are 

 carnivorous and make no burrows. A third larval 

 form is the swimming one, such as that of the common 

 Chlceon, found in pools and small streams. The tail- 

 filaments are fringed with hairs, and form an effective 

 tail-fin. The gill-plates have no filaments. Lastly, 

 there are creeping forms of may-fly larvae which live 

 in running water on muddy ground and cover their 

 gills by large leaflets. Their body is encased in a 

 layer of mud imbedded in the hairy skin, and under 

 cover of this disguise these larvae strike down their 

 prey. 



When the larvae are full grown they quit their 

 burrows or the river-bed, and make their way to the 

 surface of the water. Here a rapid metamorphosis 

 occurs, and from each larva a winged fly suddenly 

 darts away. The gills are shed, the jaws, feet, and 

 tail-filaments are modified, and the eye exchanged for 

 a many-faceted compound eye, and the single or double 

 pair of wings is suddenly expanded. The may-fly, 

 however, settles immediately after emergence, and 

 again, in a twinkling, casts a second transparent skin 

 which covers the whole body. This epiphany comes 

 upon thousands of ephemerae simultaneously, and in 



