366 Aquatic Societies 



There is little movement from place to place. The 

 larvae hang at full stretch, their pliant bodies swaying 

 with little oscillations of the current, their fans out- 

 spread, straining what the passing stream affords. 

 Each of these fans is composed of several dozen slender 

 rays, each one of which is toothed along one margin 

 like a comb of microscopic fineness, and all have a 

 parallel curvature like the fingers of an old-fashioned 

 reaper's cradle. They are efficient strainers. 



When grown the larva spins its half cornucopia- 

 shaped straw-yellow cocoon on the vertical face of a 

 ledge where the water will fall across its upturned open 

 end, then transforms to a pupa inside. The pupa bears 

 on the prothorax a pair of long, conspicuous, many 

 branched respiratory horns, or "tube gills" (see fig. 171 

 on p. 280). 



The eggs are laid at the edge of the swiftly flowing 

 water on any solid support, on the narrow strip that is 

 kept wet, and, by oscillations of the current occasionally 

 submerged. 



Hydropsyche, the seine making caddis-worm, lives in 

 sheltering tubes of silk, spun from its own silk glands, 

 fixed in position on the surface of a stone (oftenest in 

 some crevice) , and covered on the outside with attached 

 sticks or broken fragments of leaves or stones. Always 

 one end of the tube is exposed to the current, and at 

 this end, the larva reaches out to forage. Here it con- 

 structs its net of cross woven threads of fine silk. The 

 net is a more or less funnel-shaped extension of silk from 

 the front of the dwelling- tube. The opening is directed 

 upstream, so that the current keeps it fully distended. 

 The semi- circular front margin is held in place by 

 means of extra stay lines of silk. The mesh is rather 

 open on the sides, but on the bottom there is usually a 

 small feeding surface that is much more closely woven. 



