184 Fortieth Annual Meeting 



repeated in different parts of the area, and a study of the 

 river as a whole may be best organized and pursued at first 

 as a study of these typical situations out of which the whole 

 system is compounded. A large and varied group of such 

 characteristic features, all readily accessible from a single 

 center, was found at Havana, in the middle section of the 

 Illinois basin, and in that section, consequently, much the 

 greater part of our work on the river has hitherto been 

 done. There we have gained, in the course of years, a 

 fairly exhaustive knowledge of the fishes of all descriptions 

 to be found in those waters, together with an approximate 

 knowledge of the relative abundance of each in average 

 years; a knowledge of the preferred haunts and usual range 

 of the various species of fish, and some acquaintance with 

 their annual migration movements; a mass of data con- 

 cerning their associations one with another in the same 

 situation and at the same time, and the competitions for 

 food and other necessaries which these associations ex- 

 press; a fair acquaintance with both the average and the 

 exceptional food of many of the species, including most 

 of the really important kinds; a considerable body of 

 information concerning their breeding habits and their 

 spawning times and places; an accurate knowledge of both 

 the composition and the quantity of the plankton of our 

 streams and lakes, obtained by several years of systematic 

 collection, measurement, and enumeration ; a fairly full 

 acquaintance with the other animals and plants of the 

 area — those which inhabit the margin, live on the bottom, 

 or lie buried in the mud; and a considerable quantity of very 

 interesting and really important material illustrating the 

 effect on the whole system of life of the Illinois River 

 produced by the opening of the Chicago drainage canal in 

 1900. We have also made many studies of the waters 

 themselves in respect to their physical and chemical char- 

 acteristics and peculiarities under varying conditions and 

 at various seasons, and have begun similar studies of the 

 mud and other materials of the bottoms of lakes and streams. 



