NORTH AMERICAN CADDIS-FLY LARVE. 
entrance to the case, the other in the end being plugged with silt 
or with small pebbles. Sometimes the chamber curves downward 
without forking, as in figure 151. The chamber is always lined 
with silk. (Figure 151 represents a case with the silk tube cut 
away, except around the larva.) Although there is considerable 
variation in the size of the twigs used, their average size increases 
with the growth of the larve. To ascertain how the change in 
cases is made, several experiments were made with captive larve. 
Some were removed from their cases and put in cages with twigs 
of appropriate size. These larve did not attempt to use the wood 
for making new cases, but merely spun silken tubes to which 
particles of silt adhered ; others, which had one side removed from 
their cases, repaired the damage with silk and silt. One larva 
repaired the damaged side with silk and fragments of bark and 
then proceeded to cut away the two ends of its case. It worked 
from the damaged side of the case, cutting narrow incisions across 
the twig until the opposite side was reached. The operation of 
cutting the two incisions across the twig ten millimeters in diam- 
eter consumed about twenty-four hours. ‘Two specimens, which 
were retained in aquaria in the laboratory, attached the anterior 
ends of their cases securely, by means of silk, to the ends of solid 
twigs, and then drilled into the wood, emitting, during the task, 
an abundance of very finely-powdered wood. One of these new 
dwellings proved too long for its occupant. It was accordingly 
girdled with a circular incision, which was deepened until one end 
of the twig was completely cut away. Several sticks similarly 
ringed were found in the creek where the larvee occur. No doubt 
this is the usual method of changing cases, as larval growth pro- 
ceeds. 
FAMILY ODONTOCERID. 
This small family is represented in the American fauna by 
but a single species with known immature stage. 
DistiNcrivE CHaracters.—The labrum is distinctly longer 
than broad. The pronotum and mesonotum are chitinized; the 
metanotum has four chitinous plates, the two median of which 
are much broader than long, crossing the median line. 
The Head.—The head is depressed in form. The labrum is 
longer than broad, with two pairs of cycle-shaped, pale sete on 
g2 
