62 



IXSECT ARCHITECTURE. 



into a roundish ball, and in tlie interior of this forms a cell 

 for its abode. The following figure from Eoesel will give 

 a more precise notion of this stnicture than a lengthened 

 description. 



Another of these aquatic architects makes choice of 

 the tiny shells of young fresh-water mussels and snails 

 (Planorbis), to form a moveable grotto; and as these 

 little shells are for the most part inhal:>ited, he keeps the 



Shell Nests of Caddis- "VVonns. 



poor animals close prisoners, and drags them without 

 mercy along with him. These grotto-building grubs are 

 by no means uncommon in ponds ; and in chalk districts 

 such as the country about Woolwich and Gravesend, they 

 are very abimdant. 



One of the most surprising instances of their skill occurs 

 in the structures of which small stones are the principal 

 material. The problem is to make a tube about the wddth 

 of the hollow of a wheat-straw or a crow-quill, and equally 

 smooth and uniform. Now the materials being small 



