CADDIS FLIES. 385 



mixed structures, where the Caddis has combined shells with the 

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

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

 them back to back on its house. Beside 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 

 I'ond-snail and fastened it to the case ; and there is an example 

 where the chrysalis of some moth, apparently belonging to the 

 genus Porthesia, has been blown into the water from a tree over- 

 hanging the stream, and seized upon by a Caddis as an 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 quarry 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 Caddis larvse to build their nests of the most extraordinary 

 subtances, such as gold-dust, crushed glass, and other sixbstances. 

 They would not, however, use beads, or anything where the 

 surface 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 

 entirely, on animal food. When the larva has lived for its full 

 period, 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, 

 therefore, to compensate for the immobility of the case, the 



c c 



