132 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, Notonecia, 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 



