
1914] Biology of Net-Spinning Trichoptera 263 
watching for prey. There is often at least one side passage 
branching off from the main tunnel. Another type is a funnel- 
like net spun between the angles of the main stalk of the grasses 
and the side shoots, and fastened at the upper end to leaves as 
Potamogetons. 
On account of lack of light the study of the nets of Holo- 
centropus picicornis Steph. was unsatisfactory. The deep 
brown color of the nets was due to a thick deposit of iron 
bacteria. 
The larva of Cyrnus flavidus McLach. lives in lakes in 
the Chara-and Elodea-zone at a depth of about 4m. In summer 
the larva spins funnel-shaped nets to the leaves of Potamogeton 
lucens when it reaches the surface. In the autumn long threads 
emerging from the plants are seen floating about in every 
direction. Plancton organisms become entangled in the threads 
and the larva runs along these and siezes its prey. In October 
and November the larve sink down with the Potamogeton on 
to the Elodea and Chara zone again. 
In a little arm of Cascadilla Creek (See Plate XXXVI, 
Fig. 1) where the water is rather quiet and from 11% to 2 feet 
deep, larve of two genera are found belonging to this family. 
The larva of Cyrnus pallidus (?) is small—8 mm. long by 1.2 
mm. broad—very rapid in its movements. The body is whitish, 
dorso-ventrally flattened; the head yellowish with a large 
brown spot covering almost the whole dorsal surface. In the 
centre of this spot is a yellow cross-shaped figure and eleven 
yellow dots around the margin. The yellowish pronotum is 
brown posteriorly with yellow dots. On removing a stone 
from the water the dwellings of this larva might easily be 
overlooked, for they resemble patches of sediment clogging 
the crevices. If placed in a pan of water, however, and ex- 
amined under the microscope, they prove most facinating 
objects for study. Stretched across crevices in the stones, 
preferably along its edges, but also occasionally on the upper 
and lower surfaces is the roof of the larval dwelling. The tube 
of a full grown larva, is about 9 mm. long by 3 mm. broad and 
is dorsoventrally flattened. (See Plate XXXVIII, Fig. 2). 
It is spun of fine silken threads so closely woven that it has a 
felty texture. It is always brown with a coating of diatoms. 
At either end a little flap hangs from the roof which acts as a 
