11 
and a study of the river as a whole may be best organized and pur¬ 
sued 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 approxi¬ 
mate 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 concerning their associations one with 
another in the same situation and at the same time, and the compe¬ 
titions for food and other necessaries which these associations ex¬ 
press ; a fair acquaintance with both the average and the excep¬ 
tional food of many of the species, including most of the really im¬ 
portant 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 con¬ 
siderable quantity of very interesting and really important material il¬ 
lustrating 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 majde many studies of the waters themselves in respect to 
their physical and chemical characteristics and peculiarities under vary¬ 
ing conditions and at various seasons, and have begun similar studies 
of the mud and other materials of the bottoms of lakes and streams. 
In this general field we now need merely to finish our studies 
along special lines, and to extend somewhat the geographical range 
of our detailed survey. We shall then be both ready and free to 
take up special problems of immediate economic interest. Indeed, 
much has already been done by us on such practical problems, as may 
be seen from a few illustrations. 
We learned a good many years ago—and this fact was first es¬ 
tablished in Illinois—that virtually all our young fishes, whatever 
their adult habits may be, live at first on the same kind of food. All 
which hatch in like situations and at approximately the same time, 
consequently, compete with each other when they first begin to feed. 
