152 



INSECT LIFE. 



in this rude retreat is a fisherman, and stretched be- 

 tween two stones near-by can be seen his net. 



This is made of silk. It is usually funnel-shaped, 

 opening up-stream, and in the center of it there is a 

 portion composed of threads of silk extending in two 

 directions at right angles to each other, so as to form 



meshes of surprising regu- 

 larity. It is as if a spider 

 had stretched a small web 

 in the water where the cur- 

 rent is swiftest (Fig. 123). 



These nets occur in rap- 

 ids between stones, but in 

 many places they are to be 



^'''" '^^■^Sike'l^orm."^"'^'^'"^ ^^""^ ^^ greater numbers 



along the brinks of falls. 

 Here they are built upon the surface of the rock, 

 in the form of semi-elliptical cups, which are kept 

 distended by the current. Much of the coating of 

 dirt with which these rocks are clothed in summer 

 is due to- its being caught in these nets. 



It is usually difficult to procure specimens of these 

 nets for preservation ; sometimes, however, one can 

 be found attached to the surface of a single small 

 stone or to a piece of wood in such a way that it can 

 be removed from the water without injury to it. 



Find some net-building caddice-worms and learn 

 all you can regarding their ways ; collect specimens 

 for your collection and for study ; compare their 

 structure with that of other caddice-worms ; pre- 

 serve specimens of larvae in alcohol ; and dry, if pos- 

 sible, some of their nests and nets. 



Write an account of these insects. 



