254 NATURAL HISTORY OF AQUATIC INSECTS CH. 



out of these leaves, and fastened them to its sheath^ 

 placing some of them transversely in the manner 

 already described. When the outside of the sheath 

 had taken the desired form, the larva worked at the 

 inside, spinning a silken lining of a substantial kind. 

 I have since seen several larvae of the same species 

 at work, making new sheaths, lengthening or 

 strengthening the old ones, adding new fragments 

 cither to increase or diminish its weight, and all that 

 I have been able to see was merely a repetition or an 

 adaptation of the operations just described. [The 

 cases of small stones or sand are the hardest to make. 

 A Caddis-worm will complete one of these in five or 

 six hours.] 



"In some species (such as Phryganca grandis) the 

 sheath appears to be rolled spirally round, like a 

 ribbon wound upon a stick. I have seen bits of oak 

 leaf arranged in this way along some very large sheaths 

 which I found in a pond in the Bois de Boulogne. 

 Some of these were only covered for part of their 

 length by bits of broad leaves, the rest being occupied 

 by narrow strips arranged side by side so as to form 

 a spiral band extending to the higher end of the 

 sheath. The larvae which inhabit these last sheaths 

 have two parallel curved bands on the front of the 

 head. 



" The larvae of a very small species [Triaenodes 

 bicolor] are also covered by a spiral band, and look 

 as if a green ribbon had been bound round them from 

 head to foot. The dress of the larvae is like our own 

 in one respect ; it is much handsomer when it is new. 

 The colour changes in time from a beautiful green to 



