1914] Biology of Net-Spinning Trichoptera 259 
FAMILY PHILOPOTAMIDZ. 
The only descriptions of catching nets of this family are 
those of Thienemann. He gave a brief account of a net of 
Philopotamus ludificatus in 1906; as I was unable to obtain this 
paper, however, I will summarize a fuller description which 
appeared in 1908. 
Two similar species P. ludificatus McL., and P. montanus 
Don., are found in great numbers in the swift mountain brooks. 
of Middle Europe. These build dwellings which are very 
much alike. The house is a broad sac-like structure of loose 
mesh about as long as one’s finger. At the front end where the 
opening is found, it is fastened to a stone on the bottom of the 
brook. The blind end of the sac floats freely; and in the bot- 
tom of it is found the larva which can feed on organic particles 
caught in the net. Occasionally the larve also stretch their 
houses between two neighboring stones and so construct for 
themselves, in this way, a kind of catching-net. Only one 
larva is found in each net. 
No descriptions have appeared before of nets of the Genus. 
Chimarrha. The nets of Chimarrha aterrima, which I found, 
are long, narrow pockets built entirely of a very fine mesh of 
delicate silken threads. (See Plate XX XVIII, Fig. 1). The 
average size of the net of the growing larva is about 25 mm. 
long and 3 mm. wide. The nets are rarely found singly, but 
generally placed five or six in a row. Sometimes the front 
edges of these are joined together, but in most cases each net 
is entirely separate from that of its neighbors. There is a 
large opening at the end facing the current, and a tiny opening 
at the hinder end just large enough for the larva to slip through 
and make its escape when alarmed. This opening is very hard 
to see, not only because of its size, but owing to the fact that 
the nets are generally brown with a coating of diatoms, etc., 
over much of their surface. The nets are fastened at the en- 
trance by their entire lower edge, the rest of the sac floating 
freely, and kept distended by the current. They are found 
fastened to the underside of stones or to their upper surface 
when they are covered by other stones. I have also exposed 
them on the upper surface of the shelving rocks by pushing 
aside the covering mats of Cladophora. The orange or yel- 
lowish larva, of which there is only one to a sac, is usually seen 
