VEGETATION COMMUNITIES 131 
all the species are relatively independent of the atmosphere and of the 
bottom. 
c) Emerging vegetation association of bays.—Such situations as are 
occupied by this association are found in bays and protected situations in 
the larger lakes and represent a stage which is last in the history of a 
lake. Water-lilies, water buttercups, and Myriophyllum are the prin- 
cipal plants. Filamentous algae are usually very abundant. Logs, 
sticks, and pieces of wood are not uncommon. 
On the under side of logs, we find such forms as the polyzoan 
(Plumatella) and sponges (Spongilla sp.). On the under side of the water- 
lily pads are usually numbers of Hydra together with great numbers of 
Fic. 82.—A muskrat’s nest adjoining the lake border among the bulrushes on 
sandy bottom. 
shelled protozoans and rotifers, especially sessile forms. Snails also are 
common here (Segmentina armigera, Planorbis parvus, Physa gyrina and 
integra, Planorbis campanulatus, and some species of Lymnaea). 
A large number of species of aquatic insects cling in the vegetation 
with the abdomen near the surface of the water and secure air through 
various anatomical arrangements which conduct it to the spiracles; the 
most noteworthy of these are the water scorpion (Ranatra), the electric- 
light bugs (Benacus and Belostoma), the predaceous diving beetles 
(Dytiscidae) (ggc), the water scavengers (Hydrophilidae), and the water- 
boatmen (Corixa). There are also a number of aquatic insects that are 
not dependent upon the atmospheric air in their young stages. They 
require, however, some object which reaches above the surface of 
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