THE NATURAL HISTORY SURVEY. pid | 
along the borders of a stream be examined it will frequently 
yield a rich harvest of small snails. In other words any cool 
place where there is plenty of shelter and moisture will be 
found a good locality for these animals. In forests mollusks 
will be found abundantly where soil is plentiful and where 
there are numerous open spots. They will not be found in 
woodlands of spruce or pine. 
When search is being carried on for the animals and shells 
the eggs should not be forgotten, for they are of great impor- 
tance. These will be found in about the same localities as the 
mollusks themselves, in cool, moist places. They may be 
known by their white color, leathery texture and the pellucid 
membrane in which they are enclosed. They resemble little 
balls of jelly, and are generally found in a mass, although de- 
posited singly. Since the embryological development of but 
few mollusks is known, any careful student may find here a 
wide field for original investigation. 
If it is found desirable to keep some of the animals alive 
they may be put ina box filled with moist earth. A large fish 
globe is very useful for this purpose. Everything done by the 
animals should be noted, especially the manner of eating and 
kind of food taken. 
2. FRESH-WATER SPECIES. 
Both gastropods and pelecypods are found in fresh water. 
Any region having ponds, streams, ditches, brooks, etc., will 
support a fresh-water molluscan fauna. 
a. Hasitat.—A body of water with a quantity of lime in 
solution and with a muddy bottom will yield the largest variety 
of mollusks, since lime is essential to the building up of the 
-shell. A coarse crystalline gravel is less adapted to them than 
is soft, less gritty sands and mud. , 
A rapid current is not favorable, although a number of 
mollusks (as the Pleuroceridz) are found on rocks over which 
a rapid stream is flowing. A stream filled with decaying vege- 
tation is unsuited to molluscan life from the presence of car- 
bonic acid (CO,) arising from its decay. This not only affects 
tne life of the animal, but causes an excessive erosion of the 
shell, in the repair of which the animal is weakened by the 
enforced secretion of shelly matter. 
Gill-bearing mollusks will not voluntarily inhabit a stream 
holding impalpable mud in suspension, nor in waters charged 
