io8 ROD AND RIVER 



other like the needles of a stocking - knitter. 

 Most of these cases are balanced by a stone. 



' Next come a number of cases which are com- 

 posed of small shells, those of the Planorbis being 

 the most common, and having among them a few 

 specimens of the Limnaea, or pond-snail, and 

 many separate valves and perfect shells of the 

 fresh-water mussel. The caddis larva is an in- 

 corrigible kidnapper, seizing on any shell that 

 may suit its purpose, without troubling itself 

 about the inhabitant. It is quite a common 

 occurrence to find four or five living specimens 

 of the Planorbis and Limnaea affixed to the case 

 of a caddis larva, and to see the inhabitants 

 adhering to the plants and endeavouring to pro- 

 ceed in one direction, while the caddis is trying 

 to walk in another, thus recalling the well-known 

 episode of the Tartar and his captor. In these 

 cases the cylindrical body is made of sand and 

 small fragments of shells bound together with a 

 waterproof cement, and the shells are attached 

 by their flat sides to the exterior. 



' There are several cases which are made entirely 

 of sand cemented together, some being cylindrical, 

 and others tapering to a point, like an elephant's 

 tusk. There are also examples of mixed struc- 

 tures, where the caddis has combined shells with 

 the leaf and twig case, and in one of these in- 

 stances the little architect has bent back the 



