264 Annals Entomological Society of America  [Vol. VII, 
stopper, closing against the opening when the stone is removed 
from the water. Radiating in all directions from the floor 
of its retreat, at either end, may be seen threads of silk about 
7 mm. long. These are fastened to the stone at their outer 
ends and a microscope reveals the fact that they are connected 
with one another by a loose irregular mesh which floats up from 
the surface of the stones and entangles many small organisms. 
The larva lurks in its little cave, and welcomes visitors gladly 
at its front or back door. Any movement on the silken strands. 
in front of its doors causes it to dart out the front part of its. 
body with lightning-like rapidity, sieze the intruder and draw 
back again, all in the twinkling of an eye. Large numbers of 
Vorticella and other Ciliates, rotifers, Chaetonotus, Chirono- 
mids and diatoms were found entangled in the meshwork. 
The larva of the Polycentropus sp. (?) is large and more 
deliberate in its movements. It is 19 mm. long and 2 mm. 
broad; the head and prothorax yellowish-brown with many 
small, brown dots, and the abdomen of a pinkish-lavender color, 
iridescent when the sunlight strikes it. It sometimes looks. 
bluish. The larva lives on the under side of stones in a deli- 
cate silken dwelling which falls together into an unrecognizable, 
brown slimy mass when removed from the water. It was not 
until I had examined a large number of these nets that I was. 
able to detect a trace of any definite form. The larva lives in a 
very delicate, silken tube fastened to the stones along its whole 
undersurface. It is shaped like a flattened cylinder and slightly 
curved. (See Plate XXXVIII, Fig. 3). The tube is 21 mm. 
long and 5144 mm. wide with an expanded opening at either end. 
Connected with each opening and along either side is a mass of 
tangled, silken threads, about 20 mm. square and loosely 
attached to the stone. This tangled mass may float partially 
over the tube and so obscure it. 
I have never observed the larva feeding but do not doubt 
that Mayfly nymphs and Chironomid larve become entangled 
in the meshes as they crawl about over the stones, for remains. 
of these forms are abundant in the stomach contents. 
