6 
its banks, are the principal causes of differentiation in different parts 
of its course,—differences which express themselves most vividly in 
the amount and character of the plankton, but which are reflected 
also more or less definitely in the general aspect of its biology. 
Since last July our work has been carried forward under the 
immediate charge of Mr. R. E. Richardson. It has been mainly 
directed to a comparison of present conditions with those of the 
period preceding the opening of the drainage canal, and to the col¬ 
lection of materials for a fuller study of the food of fishes than has 
hitherto been made and for a comparative study of the contents and the 
physical and chemical condition of the bottom in several selected 
situations, as related to differences in the plankton and other bio¬ 
logical products. From weekly collections, begun August 20 and 
continued for four months, we learned that the yield of plankton 
in the main stream per cubic meter was then, at Havana, approximately 
double that of our earlier period, notwithstanding the fact that the 
water-level is about three feet higher on an average than it was 
before the opening of the drainage canal. 
Our main objects for the coming two or three years will be to 
complete a comparison of present conditions with those of the former 
time; to study the river as a unit with reference particularly to its 
economic values, its protection, and its improvement; to work out 
the details of its biological regimen by a study of the influence of 
the various conditions affecting the course of events in various sit¬ 
uations ; and to carry out comparative studies between the Illinois, 
the Mississippi, and the Missouri—all readily accessible from our 
location and by means of our equipment. It is a large, a fruitful, 
and an important field of research, and we invite the cooperation of all 
so situated as to contribute to our knowledge of any part of it; 
and to this end investigators will be admitted to our Havana station 
at any time after June 1. 
