The Caddis-Worm and its Souses. 311 



worms, that they often completely stupefy the creatures, and 

 sometimes even cause their death. If pieces of pine wood be 

 placed in a vessel, and if a caddis be kept amongst that wood, 

 in a short time it becomes stupefied, and would ultimately 

 die if suffered to remain. This stupefaction is caused by the 

 turpentine which is contained in such large quantities in all 

 kinds of pine wood. 



Slate is another substance which caddis-worms are unable 

 to employ for their building. I attribute this to a similar cause 

 as that which prevents caddis from using pine wood, namely, 

 the odour. In these cases, however, the substance does not 

 cause any injury to the worms. The same obstacles arise 

 with both coal and brick. 



Although there are many kind of metals that can be em- 

 ployed by caddis-worms, yet there are some from which they 

 are quite unable to construct their houses, such, for instance, 

 as lead and copper. I have myself repeatedly endeavoured to 

 get a caddis to use these metals just named, but it was always 

 in vain ; although worms would try again and again to build 

 from them, they invariably failed. 



It will always be found that if any caddis is not able to 

 construct itself a house from any kind of substance which 

 might be given to it, no other caddis could form a house from 

 the same material. Any number of caddises may be tried for 

 that purpose, yet the results are always the same. 



It has before been stated that the weight of caddis cases 

 depends upon the locality that is inhabited by the worms, for 

 it is found that the more rapid the streams, the heavier are the 

 cases. 



When a caddis is turned out of its house, the whole surface 

 of its body is covered with air-bubbles. Now, if these crea- 

 tures are placed under these circumstances in running water, 

 they speedily rise to the surface and float, until at last they 

 die from exhaustion in their struo-o-les to regain the bottom 

 of the water. 



This being then the use of the cases to the caddises, let us 

 now see the manner in which they construct them. It is, 

 indeed, an interesting sight to watch them during the progress 

 of their building. The worms commence by placing together 

 a number of pieces of the substances they wish to employ. 

 These are then cemented loosely together, so as to make a 

 foundation for building its subsequent structure. These first 

 pieces that are used as a foundation arc always cast off before 

 the completion of the edifice. The cement used by the caddis 

 in fastening the pieces of its house together, is a secretion 

 which proceeds from its mouth. With it the different pieces 

 are fixed together in the most perfect manner. This cement 



