and year out, was 2.7 parts per million, and the total average amount 
of plankton moving down stream past Havana reached the astound¬ 
ing aggregate of three hundred and fifty thousand barrels, or seven¬ 
ty-five thousand tons, per annum, equal to eight and a half tons per 
hour the year round. This was about fifteen times the total weight 
of the fish then taken from the river each year. 
Besides our plankton studies made at the various Havana sta¬ 
tions, each representative of a characteristic aquatic situation, a 
beginning has been made in a study of the system of the entire 
stream, taken as a single unit of environment. For this purpose, 
trips by steamboat were made for considerable distances, with con¬ 
tinuous plankton collections throughout each trip. Longitudinal bio¬ 
logical sections of the stream were thus made, aggregating four 
hundred and fifty miles for the Illinois river and three hundred and 
sixteen miles for the Mississippi, from St. Louis to Quincy and re¬ 
turn. On the first trip, made in May, 1899, an iron pipe delivered 
a continuous stream of water into a plankton-net which was lifted 
and emptied every twelve miles. In all the other trips a steam 
pump was used to supply a continuous current, which was passed 
through a meter, enabling us to determine precisely the amount of 
water strained. 
By such studies one gets a vivid idea of the individuality of the 
river as an organism, and of the complexity of its structure and the 
sensitiveness of its physiological reactions. A stream like the Illi¬ 
nois, with its flowing current, varying in rate in different parts of its 
course, variously fed by streams, by lakes, by marshes, and by under¬ 
ground springs, temporarily influenced and often profoundly af¬ 
fected by local storms, by drouth, by floods, is a very different sub¬ 
ject of study from a lake, and to me a far more interesting one. A 
lake is sessile, simple, stolid, coelenterate; a river is motile, com¬ 
plex, sensitive, and articulate: a lake has an aspect, a constitution; 
but a river has a character, a behavior. The river has also a spe¬ 
cial attraction to the student of biology in that it is more readily 
analyzable than a lake, into distinct and largely independent sec¬ 
tions or situations which can be studied separately and as a series. 
For a discussion of our data of continuous collection, we have 
divided the Illinois from Hennepin to its mouth, the part patrolled 
by us, into six sections, each with its well-marked individuality. 
The slope of the bed, the extent and nature of the bottom-land 
waters feeding the main stream, the size, length, and number of its 
tributaries, and the contributions of sewage waste from towns upon 
