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. In a 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 lields 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 limnology. 



ACKNOWLEDGMENTS. 



For more than a score of years Professor S. 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 lies 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- 



