150 INSECT LIFE. 



above, can be kept in aquaria, and are excellent sub- 

 jects for study. 



In swiftly flowing streams, and especially in those 

 in which the water is cool, there may be found many 

 other kinds. Several of these build cases of small 

 stones or grains of sand. Some of the cases are very 

 regular in form ; others consist of a central tube with 

 large stones fastened on two sides of it (Fig. 120); 



FIG. 120. FIG. 121. FIG. 122. 



and one kind, built of fine sand, is coiled so as to 

 resemble the shell of a snail (Fig. 121). 



In all of these the material of which the case is 

 made is fastened together by silk, which the larvas 

 spin from the mouth in the same manner as caterpil- 

 lars. In some species the case is composed entirely 

 of silk. Fig. 122 represents the form of such a case 

 made by a larva that lives among eel-grass in a lake. 



Before transforming to pupae, the caddice-worms 

 partly close their cases so as to keep out intruders, 

 but openings are left for the inflow of water for 

 breathing. 



The adults are known as caddice-flies ; they are 

 mothlike insects, which are often attracted to lights 

 at night. Fig. 68, page 79, represents one of them. 



Collect as many kinds of caddice-worms as possi- 

 ble. Keep alive some of those that will live in 

 aquaria, and study their habits. 



Remove some from their cases, and study their 



