NATURE'S CRAFTSMEN 



done by creating for our net-making cacklis an artificial 

 environment that may tempt it to show its methods. 

 A long, shallow pan filled with water was transformed 

 for the nonce into a miniature brook, and in it were 

 placed several stones with hydropsychid cairns built 

 upon them. The collection was taken to the house 

 and put under observation. Soon the larvse, who easily 



NET-MAKING CADDIS WORM BUILDING ITS UNDER-WATER CAIRN 



The upper figure shows an earUer stage, the lower the pebble wall 

 further advanced 



knew that something out of the way had befallen them, 

 crawled from their dens. Then the stones were re- 

 moved, and over the bottom of the pan, which had been 

 covered with sand, were strewn pebbles like those of 

 which the cairns are composed, and the long watch for 

 building operations began. 



Let us follow the behavior of one nearly full-grown 



278 



