228 ILLINOIS ACADEMY OF SCIENCE 
but it is known that many of them live through the winter 
as larvae and transform in June or July. When the larvae 
are ready to pupate they either fasten the case to some larger 
object, and Close the other end, or they close both ends with a 
web of silk and frequently fasten on a pebble or a bit of stick. 
They are completely helpless while transforming. The pupae 
differ from the larvae in having larger mandibles with which 
they cut their way out of the case, and usually swimming hairs 
on the mesothoracic legs. Most of the larvae which inhabit 
movable cases transform to pupae which have respiratory fila- 
ments much like the larvae. The pupae have rows of hooks on 
several dorsal segments which hold them in the case. 
The larvae, which live in fixed cases, build them in the 
same way. Sometimes their cases are only tubes of silk, 
which are found on the bottom of the stream or on the sur- 
face of sticks and stones. Others are of various shapes and 
generally covered with sand, pebbles, or leaves. Certain spe- 
cies build their cases in the form of a snail's shell, which are 
covered with sand, and some of these were described as snails' 
shells. 
The larvae inhabiting these fixed cases are mostly of another 
type of body, which is not as strongly curved. They have no 
hooks to hold them to the cases, and although the majority 
breathe by means of respiratory filaments, a number of them 
breathe by means of spiracles. They pupate in much the same 
way as the larvae inhabiting movable cases and the pupae 
strongly resembles the larvae, differing in the larger man- 
dibles and the swimming hairs on the mesothoracic legs. In 
some species the respiratory filaments are lost during pupa- 
tion and the pupa breathes by means of one large spiracle lo- 
cated in the conjunctiva between the prothorax and mesotho- 
rax. 
The most interesting species of larvae with fixed cases are 
those that spin nets, with which they catch their food. These 
nets are placed in the streams where the current is swift. They 
are usually spun somewhat funnel-shaped, so that the current 
keeps them expanded. These larvae often do not build a case 
but hide in masses of rubbish near where they have spun their 
nets. Those which spin cases often place them side by side, 
so that there is quite a colony. 
