THE ANIMALS OF THE FRESHWATER AQUARIUM in 



terity, in spite of the often heavy case which must be dragged 

 behind them. Much as in the case of the hermit-crab (g.v.\ 

 to which the caddis show certain analogies, the part of the body 

 which can be extruded is covered with a firm coat, while the 

 remainder is soft and delicate. Again, much as the hermit is 

 fixed to its borrowed shell by a strong hook in the posterior 

 region, so the caddis is fixed to its case by two posterior hook- 

 like processes. In both cases, therefore, a direct attempt to 

 extract the creature leads to disaster. In the caddis, however, 

 the tube is open at the posterior as well as at the anterior end, 

 and fishermen have long since found that the insertion of a blade 

 of grass into the posterior end will cause the larva to relax its 

 hold and leave its tube. It will then speedily build a new one, 

 and the process may be watched in detail. The above operation 

 is not, however, really necessary in order to see the caddis build, 

 for if they be put into a vessel containing any building material 

 different from that abundant in the pond from which they came, 

 they will be seized with a desire to replace the old material on 

 their backs by the newer. The teacher who shows caddis to 

 her class will, of course, also draw the attention of its members 

 to its very charming description of their habits to be found in 

 Kingsley's Water-babies. 



For the teacher's purposes the specific names of the caddis 

 are of very little importance, but for convenience of reference to 

 systematic books it may be well to note that cases neatly con- 

 structed of tiny particles of sand, and having a conical and 

 slightly curved shape, are due to the activity of Sericostoma 

 multiguttatum ; those ornamented with short pieces of vegeta- 

 tion, or of fragments of stick, are inhabited by species of Phyry- 

 ganea ; in P. lunaris the pieces are laid side by side running 

 parallel to the long axis of the case. Very curious are the cases 

 of the species of Limnophilus, which are often constructed of the 

 shells of living molluscs, who may be seen vainly endeavouring 

 to extricate themselves from their very constrained position. 

 Other caddis again content themselves with the hollow stalk of 

 an aquatic plant, or merely weave together any kind of debris. 

 The most interesting forms are those whose cases are unattached, 

 but as already mentioned some fasten their houses to stones. 



