VEGETATION COMMUNITIES 129 
is left with the greater part of its shallow water of the type which we have 
described. Vegetation is present from the first in the form of floating 
microscopic plants, and the dead bodies of these and of the animals 
present are swept into the depressions and protected situations where the 
waves do not drag on the bottom. Here vegetation grows in the greatest 
luxuriance and causes the production of more plant débris, which adds 
to that already in the protected situations. We then have, after a time, 
a covering of the bottom by the humus and conditions unfavorable for 
most bottom animals. The animals of the bare bottom shoals are no 
longer presentinnumbers. Small, apparently stunted forms of Lampsilis 
luteola are found for a time, but are soon driven out by the increase of 
humus and vegetation. The early vegetation is made up of scattered 
aquatic plants, such as Myriophyllum and Elodea, and in the shallower 
water usually bulrushes. 
One of the most distinctive and characteristic forms of such lakes is a 
transparent true shrimp (Palaemonetes paludosus), about 2 inches long 
(Fig. 78), which is a close relative of some of the edible marine shrimps. 
In spring they are found carrying numbers of green eggs attached to the 
appendages of their abdomens. Another common animal in these 
situations is the large polyzoan (Pectinatella magnifica). This is a 
colonial form which reproduces by budding in several directions. It also 
secretes a clear and transparent jelly. As the number of animals 
increases the amount of jelly increases on all sides and the animals are 
arranged on the outside of the more or less spherical mass of jelly; the 
necessary increase in surface for the growth of the colony is supplied 
through additional secretion by each new animal added. Some of these 
masses of jelly reach a size of 6 inches in diameter. They are often 
attached about a stalk of Myriophyllum as a center. In the autumn 
they form bodies known as statoblasts (Fig. 77), which are disk-shaped, 
the center containing living cells and the rim being filled with air-bubbles. 
The rim of the disk is supplied with hooks which catch onto objects. 
Probably they must be frozen before they will grow into new colonies 
for they do so only in the spring. 
Other characteristic animals of this open-water vegetation are 
shelled protozoa (Fig. 79), water-mites (Fig. 80), and ostracods (Fig. 81). 
On the stems of the water plants, such as bulrushes and pickerel weed, 
are the snails (Ancylus) which belong to the lunged group, but are said 
to take water into the lung and thus do not need to come to the surface 
for air.. Occasional snails, leeches, and midge larvae occur. Water- 
mites fasten their eggs to the bases of the aquatic plants. Among the 
