CADDIS FLIES. 405 



mixed structures, where the Caddis has combined shells with the 

 leaf and twig cases, and in one of these instances the little archi- 

 tect has bent back the valves of a small mussel, and fastened them 

 back to back on its house. Besides these there are one or two 

 very eccentric forms, where the Caddis has chosen some objects 

 which are not often seen in such a position. The seed-vessels of 

 the elm are tolerably common, but I have several specimens 

 where the Caddis has taken the operculum of a dead Pond-snail 

 and fastened it to the case ; and there is an example where the 

 chrysalis of some moth, apparently beloaging to the genus Por- 

 thesia, has been blown into the water from a tree overhanging 

 the stream, and seized upon by a Caddis as a unique ornament 

 for its house. These latter examples were found in a stream in 

 Wiltshire, and the tusk-like sand-cases were found in a disused 

 stone quary in the same county. 



Various experiments have been tried upon the larva of the 

 Caddis, in order to see its mode of building. A lady, Miss Smee, 

 has been very successful in this pursuit, and has forced the Cad- 

 dis larvae to build their nests of the most extraordinary sub- 

 stances, such as gold-dust, crushed glass, and other substances. 

 They would not, however, use beads, or any thing where the sur- 

 face was smooth and polished. 



In this remarkable sub-aquatic home the Caddis larva lives in 

 tolerable security, for the head and front of the body are clothed 

 in horny mail, and the soft white abdomen is protected by the 

 case. The food of the Caddis is generally of a vegetable nature, 

 though there are one or two species which live partly, if not en- 

 tirely, on animal food. When the larva has lived for its full pe- 

 riod, and is about to change into the pupal condition, it closes the 

 aperture of its case with a very strong net, having rather large 

 meshes, and lies securely therein until it is about to change into 

 the winged state. It then bites its way through the net with a 

 pair of strong mandibles, comes to the surface of the water, breaks 

 from its pupal envelope, and shortly takes to flight. The larger 

 species crawl up the stems of aquatic plants before leaving the 

 pupal skin, but the smaller merely stand on the cast skin, which 

 floats raft-like on the water. 



There are one or two species whose cases are not movable, but 

 are fixed to the spot whereon they were made. In order, there- 

 fore, to compensate for the immobility of the case, the larva has a 

 much larger range of movement. In the ordinary species, the 



