258 THE DRY-FLY MAN'S HANDBOOK 



from which the oxygen for respiratory purposes is 

 extracted. In some cases the entrance is closed by 

 small pieces of wood, leaves or stones fastened obliquely 

 across, but never so closely as to render it impervious 

 to water. Larvce inhabiting rapid water fasten the 

 cases to weeds, heavy stones, or other solid' bodies 

 to prevent them from being carried adrift by the 

 current. 



Larvae of the family of the Rhyacophilidae which 



make fixed cases commence 

 Larvae with by selecting a heavy stone and 



fixed cases. attaching to the lower side of 



it by means of the silk a num- 

 ber of small stones, and thus constructing a closed-in 

 house, leaving only a small irregular-shaped door for 

 ingress and egress. When full grown they close up the 

 case, leaving spaces between the stones used for this 

 purpose, so that the water so necessary for respiratory 

 purposes can flow freely into or out of the little house. 

 They then become covered with a brown, hard cocoon, 

 in which they pass the rest stage while effecting the 

 change to a pupa. Larvae belonging to the family of 

 the Hydropsy chidse also make fixed cases. They, 

 however, make no cocoon, the pupae merely lying in 

 the closed-up case. In Plate XXVI Fig. i is the 

 larva. Fig. 2 the larva enclosed in the cocoon, and 

 Fig. 3 the pupa of Rhyacophila dorsalis. 



The larva, whether one of the movable or fixed 

 type, then effects the metamorphosis to the pupa, and 

 Fig. 3 of Plate XXVI shows the general appearance 



