139 



suggests their ephemeral existence. It is of these that poets have 

 sung. 



Stone-fly nymplis also cling closely to the flat stones. The cast 

 skins of these are frequently found on the banks of streams. They 

 resemble the May-fly nymphs but can be identified by comparing 

 with these illustrations. (See Fig. 93.) 



92. — The May -fly sheds its nymph shin. {Twice natural size.) 



Sometimes on the very brink of a cataract one will see what 

 appears like patches of loose black moss. Strangely enough, these 

 are the larvse of black flies, related to the terrible " Punkies " of 

 the north woods. The black fly larvae can live only in the swiftest 

 water. There they pass through their transformations and succeed 

 in emerging into their aerial stage, in spite of the rushing current. 



531 



