432 THE INSECT WORLD. 
tractile tubes. They construct for themselves fixed places of 
shelter, more or less imperfect, at the bottom of the water, and 
against large stones, which they leave occasionally for a few 
moments. Sometimes these cases contain several larve. Fig. 420 
represents the various states of a Hydropsyche ; the larva is seen 
on the left, the pupa on the right, the winged insect in the middle. 
Two of the insect’s tents, or places of shelter, are represented below. 
Fig. 421 shows the different states of Rhyacophilus vulgatus, larva, 
cocoon, pupa, and imago. The genus Rhyacophilus has this pecu- 
liarity, that the larva spins itself a cocoon in the interior of its 
dwelling before changing into a pupa. 
