26 THE BROOK BOOK 



in the current, and a chance of a plentiful supply 

 of food without the necessity of going after it. 

 They don't live long in still water. These larvae 

 have special contrivances for breathing the air that 

 is mixed with the water, as do many aquatic in- 

 sects. The great fans which you saw waving back 

 and forth have a very important function. They 

 are forced through the water, literally sweeping 

 hordes of microscopic plants and animals down the 

 hungry throats of their owners." 



"But how do they get to be flies?" I inquired. 



"They spin a kind of cocoon," he went on, 

 "in which they pass the pupa state still clinging 

 to the stone. I have never yet seen them emerge 

 from the water. Some say that they rise in a bub- 

 ble of air and escape when the bubble reaches the 

 surface. How they get the bubble, or manage to 

 get themselves inside of it, is not so easily explained. 

 I mean to find out for myself. I know they do get 

 out and fly, but I'm not satisfied with the bubble 

 theory." 



"It's a wonder they ever manage to get out, 

 isn't it?" I ventured. "And do the real black- 

 flies, the 'bity' kind, live in the water and look 

 like bits of soft mossy carpets on the rocks as 

 these did?" 



"They all live in the water during their im- 

 mature stages," he replied. "We have much to 

 learn of their habits." 



