440 
UNSOTVED PROBLEMS. 
This study, while it gives a fairly complete picture of a particular 
pond and establishes some general notions concerning ponds of this type, 
is to be regarded as opening up a new corner in the field of freshwater 
biology, rather than exhausting «ny part of it. The fauna of solution ponds 
needs to be more carefully and generally explored. The life history of 
many of the species is quite unknown. Experimental studies on the effects 
of varied conditions upon some of the organisms are certain to yield re- 
sults. The details of the mode of dispersal are very imperfectly known 
in many forms. 
The most important general investigation, it seems, is to carefully 
select a series of ponds having different combinations of environmental 
factors, i. e., area, depth, shade, plant growth, wash, etc., and to make a 
series of simultaneous observations extending over at least one year. Then 
by a process of elimination, determine the effect of these factors. 
I desire to express my obligations to Prof. C. Tf. Hyenmann and Prof. 
Charles Zeleny for their valuable suggestions and criticisms. 
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