96 
to treat with considerable detail all those more general features 
of the environment which pertain to the river as a whole, and 
which must therefore be considered not only in the discussion_ 
of the plankton of the river proper, but also in any investiga- 
tion of the bottom-land lakes and marshes. 
From the vantage-ground of the present development of 
plankton methods and in the light of the experience gained in 
the years that have passed, many deficiencies in the work will 
be evident. To none are they more patent than to the writer. 
Problems everywhere crowd for solution, and the desirability 
of additional data and supplementary work will repeatedly ap- 
pear. Ina general survey such as this, many statements of a 
more or less tentative character must be made which future in- 
vestigation alone can confirm or invalidate. Indeed, one of the 
principal values of pioneer exploratory work of this sort lies in 
the fact that it suggests new fields of endeavor. For the solu- 
tion of many of these allied problems considerable preliminary 
work has already been done, but their full discussion falls be- 
yond the scope of the present paper. 
The magnitude and complexity of the task have increased 
with each succeeding year, but it is to be hoped that the con- 
clusions here presented from the data accumulated during this 
unique opportunity for continuous and systematic observation 
upon the minute life of a river, will lead to the advancement 
of the science of liimnology. 
ACKNOWLEDGMENTS. 
For more than a score of years Professor 8. A. Forbes has 
been Director of the State Laboratory of Natural History and 
State Entomologist of Illinois. The confidence of the public 
in his good judgment which this service has inspired has been 
shown by the people, through their legislature, in repeated ap- 
propriations for the support of the Illinois Biological Station 
founded by him in 1894, an institution whose work les mostly 
in the field of pure, rather than applied, biological science. To 
him, then, is due in a very true sense the opportunity of prose- 
