SNAILS AND MUSSELS 



Fig. 238. — A Japanese student's sketch of a musk- 

 rat's pile of mussel shells. (Drawn by Fumiko 

 Mitani.) 



In his study of the food of fishes in Lake Oneida, N. Y., 

 Baker found that forty-six out of fifty-four species of fish ate 

 moUusks. The brook trout was one of only five kinds in 

 which mollusks made as little as one per cent of the whole 

 diet, on the other hand they made up twenty per cent of the 

 bullhead diet and ninety per cent of that for sturgeons. 



Collecting, aquarium study. — A good way to learn something 

 about mollusk society is by taking a census of a square 

 foot or two of the pond or brook where they live. (Fig. 

 239.) If the other organisms which are present be included, 

 leeches, dragonfly and mayfly nymphs, aquatic plants, a fair 

 picture of the community will be secured. "^ Plants provide 

 food for mollusks, mayflies compete with them for the same 

 food, leeches are rank enemies and eat them. Such inter- 

 relations can be equally well studied in lily pad, algal mat 

 and pond weed communities. Mollusks of each kind and 

 sometimes other animals too should be preserved for identi- 

 fication and record (p. 40). 



For aquarium study any pond snail is easy to keep, but 

 Physas (Fig. 248) are the most active. They will live com- 



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