CHAPTER Vit 
ANIMAL COMMUNITIES OF PONDS 
I. INTRODUCTION 
Ponds are fascinating to all, and do not lack interest from the scien- 
tific point of view. They are of especial interest to those familiar with 
the laboratory study of zodlogy. The common animals of the laboratory 
are pond animals, because pond animals are forms that will live in 
stagnant water. The common aquarium fishes are all pond fishes, as 
the brook forms die quickly if they are not supplied with running water. 
The frog, so much studied, is a pond form. The conditions in ponds are 
different from those in lakes and streams, because currents are not strong 
nor particularly important. The water doubtless piles up at one side 
or end of a pond during strong winds, and a complete circulation is 
effected, but this is not important. All of the conditions of lakes are 
duplicated in ponds, but on a smaller scale. One of the chief differences 
between ponds and lakes is the vegetation. Ponds are usually very 
largely captured by vegetation which is very much like that in the bays 
of lakes. Succession of plants in ponds is similar to that in lakes; the 
age of a pond is therefore a matter of first importance. The bottom 
materials are of most importance at the beginning (6, 112). The bottom 
materials in the ponds of the Chicago area are rock, clay, and sand. 
Rock-bottomed ponds have been but little studied, though there are a 
number of ponds in abandoned quarries of different ages which would 
make a good series for investigation. Clay bottom occurs in the moraine 
area. Nearly all the natural clay-bottomed ponds have reached a stage 
at which the bottom is not important, but one could no doubt find a 
good series if he were to make a special study. Sand-bottomed ponds 
are the commonest of all, and for the purpose of studying the effect of 
age upon ponds, a series of sandy-bottomed ponds, which differed chiefly 
in the matter of age, was selected. 
II. AREA OF SPECIAL STUDY 
The ponds that have been made the subject of special study lie in 
the sand area at the south end of Lake Michigan, within the corporate 
limits of the city of Gary, Ind. They may be reached from the stations 
known as Pine, Clark Junction, and Buffington (Fig. 84). The locality 
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