200 BIOLOGICAL RELATIONS OF AQUATIC FORMS 



2. If water plants and algae also contain chlorophyll, what is the result 

 in sunlight ? 



Conclusions. 1. Many snails eat fresh-water plants, while they in 

 turn are eaten by many fishes. What relationship, then, do water plants 

 bear to man ? 



2. Many aquatic insect larvae eat fresh-water plants, and are in turn 

 eaten by many small fish and crayfish. How are aquatic insects related 

 to water plants, on the one hand, and small fishes, on the other hand? 



3. Larger fishes, as the bass, pickerel, and pike, eat smaller fishes and 

 crayfishes, and are in turn eaten by man. Trace the importance of water 

 plants to man. 



Observation. If possible, collect some mosquito larvae (wigglers) . Put 

 them in a small aquarium, with a small perch or sunfish. A goldfish will 

 serve. Does the fish eat them ? 



Conclusion. Ordinary mosquitoes eat small organisms near the sur- 

 face, while other mosquito-like insects (chironomus) eat decaying plant 

 material on the bottom. Trace the possible relationship of decaying 

 plant material of ponds, etc., to man. 



Observations. 1. Many small algae are eaten by small crustaceans 

 (entomostraca) . These furnish food for the young of many fishes, as 

 lake herring, which in turn furnish food for lake trout. 



2. Many algae and Protozoa are eaten by small mollusks (snails, mus- 

 sels, and clams) and these in turn by the whitefish, etc. 



Conclusion. Of what importance are algae and Protozoa to man ? 

 Explain how you get your conclusion. 



Observations. 1. Many algae (as diatoms) are eaten by entomos- 

 tracans, these by the sprat, the sprat by the whiting, the whiting by 

 the cod, and the cod by man. 



2. Many algae are eaten by Protozoa and other small forms, these by 

 worms, the worms by crabs, the crabs by the cod, and the cod by man. 



Conclusion. Explain desirable conditions for producing cod for food 

 purposes on a large scale. 



Observations. 1. Many algae are eaten by Entomostraca (copepods, 

 etc.), these by the herring, the herring by the mackerel, the mackerel 

 by man. Just what food is furnished the Entomostraca by the algae ? 



2. Out of what raw materials do the algae manufacture this food? 

 Only when can chlorophyll manufacture it ? 



Conclusions. 1. What then is the relationship of weather conditions 

 to man's possible supply of mackerel ? Trace the steps in your reasoning. 



2. Explain the statement, "Our living food from the waters of the 

 globe may be said to be the diatoms (algae) and other microscopic or- 

 ganisms." 



