THE PHRYGANID^. 



36/ 



them, and only project the front part of their bodies. Should 

 any danger threaten them, or should they be alarmed, they 

 retract their bodies within the case immediately. Each species 

 makes its case in a different manner,- and employs different 

 materials. Some of the larvae of caddis flies invariably use 

 gravel or very small stones for their cases, and others the 

 small fresh-water snail and other shells, which they glue together. 

 Many use bits of stick or morsels of plants, so that each species 



THE NYMPH AND LARVA OF SPECIES OF THE GENUS Phrygaiiea. (Magnihed. ) 



may be known by its tube. Some live in fixed habitations, 

 which are made in the same manner as the others, but which 

 are not to be moved. 



So numerous were the caddis worms in the olden time that 

 a very thick limestone in the Auvergne is made up of the tubes 

 or indusiae of them. 



The larvae always live in water, and they have respiratory 

 filaments fitted for aquatic breathing upon the sides of the 

 abdomen. They have a scaly head, and the thoracic segments 

 are clothed with leathery plates. The legs are long, and the 



