200 THE UNIVERSE. 



workmen are named construct their protecting sheaths of 

 fresh-water shells ; finally, at other times they cut for this 

 purpose slender herbs, and cover their whole body with 

 them in such a manner that at the bottom of a pool they 

 look like tiny bottles of hay walking about of themselves, 

 for we do not perceive the timid inhabitants. 



However, the common Phryganea (Phryganea communis) 

 seems to give little heed to the nature of the materials it 



102. Giant Sirex (Slrex giganteus), the Larva of which gnaws Lead. 



employs, and willingly makes use of all it finds at hand. 

 Having carefully extracted several of its larvae from their 

 shelly sheaths, and afterwards placed them in vessels of 

 water, the bottom of which was covered solely with little 

 pearls of various colors, I saw them immediately set to work 

 to make a new residence, choosing here and there pearls of 

 the most different hues, in such a way that when the con- 

 struction was finished each Phryganea's dress resembled a 

 little case in mosaic, promenading on the walls of my crys- 

 tal vase. 



Other insects, instead of these portable abodes, labo- 



