478 



GENERAL BIOLOGY 



and in good condition for at least a week. Almost any 

 species that makes its cases of pieces of wood (fig. 268), or 

 stones, with or without ballast-pieces attached to the side, 

 will do. For the following experiments, handle the larvae 

 gently, with care not to do them any physical injury, and 

 leave them in clean water and comfortable conditions while 

 waiting the results of the experiments. While cutting cases 

 the larvae may be temporarily removed from them, if this be 

 deemed necessary. 



Observe the fitness of the cases for protection of the body 



Fig. 268. A'caddis-worm (Halesus sp?) and the case from which it was removed. 



(Drawings by Mrs. J. H. Comstock). 



and for escaping observation when in the natural environ- 

 ment. Observe the ordinary activities of the caddis-worms; 

 the manner in which they drag their cases about, or retreat 

 into them when disturbed. Drive a worm out of its case 

 (by poking it gently from the rear), and observe the form 

 and structures of the body and its need of protection. 



Study the case of the species selected for experiment, its 

 materials and construction. Observe the cement-substance 



