1 88 THE STUDY OF INSECTS. 



make this style of house live in still water, and may, there- 

 fore, be easily kept alive in aquaria. 



There are caddice-worm houses closely resembling in plan 

 those just described but differing in appearance, being made 

 of bits of moss. Sometimes the houses are built of leaves ; 

 these may be fastened so as to form a flat case ; or are ar- 

 ranged in three planes, so as to form a tube, a cross-section 

 of which is a triangle. 



Other Caddice-worms are masons, building their houses of 

 grains of sand or of small stones. Sometimes these houses 

 are tubes very regular in outline, being composed only of 

 grains of sand fastened together with silk ; but certain spe- 

 cies of Mason Caddice-worms fasten larger stones on each side 

 of this tube of sand (Fig. 228). Some of the species that 



Fig. 228. Fig. 229. 



build tubes of sand make spiral houses which very closely 

 resemble in form snail-shells (Fig. 229). 



Whether stones or wood are used to build these houses 

 the material is always fastened together by silk,- which the 

 larvae spin from the mouth in the same manner as do cater- 

 pillars. In some species the case is 

 composed entirely of silk. Figure 230 

 represents the form of such a case, which 

 is common in some of our lakes. 

 Among the simplest of the various forms of houses built 

 by Caddice-worms are those made by certain species that live 

 under stones in rapid streams. These consist merely of a 

 few pebbles fastened to the lower surface of a larger stone 

 by threads of silk. In the space between these pebbles the 

 worm makes a more or less perfect tube of silk, within which 



