Caddis- Worms. 203 



which weaves together a group of the leaves of aquatic 

 plants into a roundish ball, and in the interior of this forms 

 a cell for its abode. The following figure from Roesel will 

 give a more precise notion of this structure 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 inhabited, he keeps the poor animals close 



Shell Nests of Caddis-Worms. 



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 abundant. 



One of the most surprising instances of their skill occurs 

 in the structures of wKich small stones are the principal 

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



