_LIMNOPHILID. 
leaf fragments between the broad floor and roof, and lining the 
cavity thus formed with a thin but tough sheet of silk. Figure 89 
represents a cross-section of the case. 
This type of case is used during the winter and spring months. 
It is the type most frequently omitted by the larve, perhaps be- 
cause their environment does not always furnish suitable material. 
Though the broad, flat form of these cases of leaf fragments, 
with their hoods projecting over the heads of the slowly-crawling 
larve, are as nearly invisible as is possible, it seems probable that 
their most important function is to form a broad surface that will 
always remain with the same side up, and not roll in the slow 
current. 
As the larve get older, in late spring, they change the flat-leaf 
type of case to cases in which the tube is much tougher. Small 
fragments of bark are now mixed with pieces of leaves in the 
tube, the broad roof and floor of leaves is discontinued, and on 
each side of the case a heavy stick is added, which usually runs 
the entire length of the case and projects for half an inch beyond 
each end, figure 94. These “ballast” sticks have the same function 
as the flat surface of, the leaf cases—they keep the cases from 
rolling in the current. 
In changing the case from the flat-leaf type to the ballast-stick 
type, the sticks are added to the top and bottom of the leaf case, 
causing the sides of the leaf case to become the top and bottom 
of the ballast-stick case. Figures 92 and 94 represent the transi- 
tion between the flatleaf case and the ballast-stick case. 
When the time for pupation draws near the larve of Pycnop- 
syche, like several other species that use ballast sticks, cut away 
the ballasts and make rough cases of irregular construction, in 
which there is no difference between top and bottom, figure 95. 
When the case is made fast for pupation there is no longer need 
to make other provision against its rolling in the current. 
PLATYPHYLAX DESIGNATA. 
Hasirat.—The larve are abundant in the Big Springs of the 
McLean basin, and occur in less abundance in several of the near- 
by springs and spring streams. All of the waters in which the 
larve have been found are cold throughout the summer and never 
freeze in winter. It was in similar springs in Wisconsin that 
Vorhies first found the larve. 
63 
