366 
History Survey, Professor Forbes, without whose aid in these more pro- 
foundly important respects the present investigation would doubtless 
neither have been conceived or carried out in its present scope and form. 
Illustrations of Apparatus ——Fig. 1. Iron dredge, showing canvas 
protector covering posterior bobinet bag, and forward coarse-mesh bag 
hung backward inside. 
Fig. 2. Iron dredge, showing canvas protector rolled back to un- 
cover bobinet bag; and forward coarse-mesh bag pulled out in front of 
frame. 
Fig. 3. Ekman dredge, showing canvas protector covering pos- 
terior bobinet bag, and forward coarse-mesh bag hung backward inside; 
front mud shoes of Ekman design omitted. 
Fig. 4. Ekman dredge, disposed as iron dredge in Figure 2 
Fig. 5. Mud-dipper, showing bobinet bag pulled out in front of 
thimble, and canvas protector in position for drag. 
Fig. 6. Apparatus used in 1914 for collecting samples of the thin 
bottom ooze for study of the composition of the lighter detritus and the 
microorganisms entering into the food supply of the small bottom animals. 
GENERAL SUMMARY 
It is the purpose of the studies here reported to make an estimate, 
based on many quantitative collections, of the total store of animal life on 
and in the bottom sediments of different sections of the middle and lower 
Illinois River and its bottom-land lakes and on the plants of their shal- 
lower, marginal waters, to trace the causes of the wide differences in this 
respect between river and lakes and between different sections of the 
stream, to estimate, also quantitativly, thesfood resources which the bottom 
muds contain for the animals inhabitating them, and thus to trace in a gen- 
eral way the successive steps by which the organic materials in the muds 
and waters of the river system are converted into forms available as food 
for man. This is, in fact, to be regarded as essentially a soil survey of 
these aquatic public properties, for the beds and weedy margins of rivers 
and lakes are a natural soil of various fertility, of which the animals, 
mainly univalve mollusks and a few kinds of insect larvae, are the crop, 
harvested chiefly by fishes, these being harvested in turn by man. From 
this point of view the upper Illinois River is, under present conditions, 
mainly a mass of plant and animal weeds—forms which occupy the pol- 
luted waters to the practical exclusion of everything useful to human 
kind—but the current of this section carries elements of a normal fertility 
to the lower reaches of the river, depositing a large part of them finally 
in the silts and sediments of river and lake in forms available for the 
nutrition of normal aquatic life, but bearing also an immense quantity 
to the mouth of the stream where it escapes unutilized into the Mississippi. 
The river system below Chillicothe varies enormously in the produc- 
tiveness of its different parts, the richest of them being the weedy margins 
