268 NATURAL HISTORY. 
upon a pane of glass, and here the breadth and firmness 
of the attachment of the base of each footstalk were very 
manifest, seen through a small microscope. 
- 459. There is an aberrant family of this section called 
Caddice-flies, remarkable for the covering of hair with 
which both their bodies and wings are beset. The hab- 
its of their larve are very interesting. They are aquatic, 
and live in cylindrical cases open at each end. To these 
cases they attach various substances, such as bits of 
wood, weeds, pebbles, shells, etc. In Fig. 209 are repre- 
sented several of 
these tubular houses 
with various things 
attached to them. 
Av The different spe- 
Z~. cies, of which there 
are many, seem to 
have their individ- 
ual preferences in 
relation to the sub- 
stances which they 
employ; but they 
readily disregard 
these preferences when there is a lack of those materials 
which they usually prefer. They never willingly leave 
their cases, but only thrust the head and a portion of the 
body out in search of their food. When about to pass 
into the torpid pupa state, they fasten their tubular houses 
to something in the water, and then close the two ends 
with a kind of silken grating which allows the water to 
pass freely through it. When they are to assume the 
imago form, they make a hole in the grating with a pair 
of hooked jaws which they now have. They are now 
good swimmers, using chiefly their hind legs for this pur- 
pose. Coming to the surface of the water, and perhaps 
climbing up some plant, the skin of the swimmer gapes 
open, and out flies an insect about double the size of that 
