D2 COMMUNITIES OF SMALL LAKES 
water when they emerge from the larval skin. The prominent members 
of this group are the dragon-fly nymphs (Anax junius and Ischnura 
verticalis). : 
There are a few insects that are relatively independent of vegetation 
as a means of attachment. The back-swimmers are an example. They 
float or swim in the water among the vegetation. The commonest of 
these are those belonging to the genera Plea, Notonecta, and Buenoa. 
There are a few fish that have a similar habit. The top minnow 
(Fundulus dispar), which feeds at the surface, is an example. It invades 
the pools near shore and devours mosquito larvae. The young of such 
fishes as the basses and the sunfishes are sometimes taken in these 
situations. 
In the mud of the bottom there are but few animals. Some of these 
are the same species as those found in the bottom in the region of open 
water and will be discussed later. There are, however, forms that live 
only on the rhizomes of the water-lily. Certain of the leaf-feeding 
beetles (Chrysomelidae, Donacia) (109) are aquatic in the young stages. 
The female eats a hole in the leaves of the water-lilies and reaches 
through with her ovipositor and deposits the eggs in a semicircle which 
has the hole as its center. When these eggs hatch the larvae crawl to the 
rhizomes. They are not provided with gills and do not come to the 
surface for air. They have a pair of spines adjoining the spiracles. 
These spines are thrust into the plant and the spiracles which open at 
their bases come into contact with the holes; the gas in the plant and 
the gas in the air tube of the insect’s body interchange, and the animal is 
thus supplied with oxygen. When the larva is ready to pupate it spins 
a cocoon in some unknown way under water, but when it is completed 
it is filled with gas, not water, and surrounds the body of the animal. 
The animal then eats a hole, connecting the cocoon with the air spaces 
of the plant. It then pupates and is supplied with oxygen by the plant 
during the entire pupal period. 
The common painted turtle (Chrysemys marginata) and the snapping 
turtle are common in such small bays. They come out upon the logs and 
bask in the sun. The pied billed grebe builds its floating nest, and many 
other aquatic birds feed in such situations (108). 
Characters of the vegetation formation: This formation is of the 
old-pond type which will be especially discussed in the following chapter. 
There are two characters, one or the other of which is possessed by 
nearly all the animals. They depend upon the atmospheric air or must 
have the support of the vegetation, or both. The majority of the ani- 
mals of this formation stick their eggs either in or on vegetation. Such 
