96 ANIMAL COMMUNITIES OF STREAMS 
May-fly nymphs, the flattened Heptageninae, and the more or less rounded 
Siphlurus (95) (Figs. 48, 49, 50), evidently succeeding well together. 
This fact makes the value of the flattening as an adaptation appear nil. 
There are also the larvae of midges (Chironomus sp.) (98) and of horse- 
flies (Tabanus) (Figs. 51, 52). The adults of the latter deposit their 
eggs in great masses on the tops of the stones which protrude from the 
water. The stone-fly nymphs, similar to the Heptageninae May-fly 
REPRESENTATIVE AQUATIC INSECTS OF A Raprps COMMUNITY 
Fic. 39.—The net of the brook caddis-worm (Hydropsyche) seen from the front. 
Drawn from a specimen which made its case against the side of an aquarium (original). 
Fic. 40.—The same in its case with the net adjoining the opening which faces 
upstream (original). 
Fic. 41.—The larva of a caddis-fly (Helicopsyche) with a case made from pebbles, 
in the form of a spiral; 23 times natural size (original). 
Fics. 42, 43.—The water-penny larva of the brook beetle (Parnidae) seen from 
above and below (43); 23 times natural size (original). 
nymphs in form and appearance, are found here also. Perhaps the 
most bizarre of all are the water-pennies. These are round flat objects 
adhering to the under sides of stones, and not looking like animals at 
all. They are the larvae of a parnid beetle (Psephenus). Figs. 42 and 
43 show two views of a larva. The old larval back becomes the cover 
for the pupa. The adults live under the stones also and their general 
appearance is like that of the parnid in Fig. 47. Sessile or attached 
animals are common in the brooks, but their numbers vary greatly from 
