rections, such as coefficient, have been made, so that the data are 
as comparable as the circumstances will permit. The data in 
the table are derived from 642 catches, and covera sufficient 
range of seasons and years to yield averages significant of any 
larger relations existing between the several bodies of water 
examined, and also to illustrate the influence of certain com- 
mon, as well as some contrasting, factors in this fluctuating en- 
vironment, 
The backwaters in the list of stations examined by us are 
typical of practically the whole range of the bottom-land wa- 
ters of the Illinois, including, as they do, a reservoir and a 
spring-fed lake, both tributary at practically all seasons, a 
marsh, and a lake tributary for only a part of the season and 
free from vegetation. Results derived from an examination 
of these will therefore afford some conception of the relation- 
ship between the plankton of the backwaters of the stream as 
a whole and that of the channel. 
In the discussion of production in these backwaters ( pp. 
350-454) IT have noted the periods when hydrographic condi- 
tions permitted a run-off of the backwaters impounded in the 
several localities to the main channel, and instances in which 
their plankton contents served to increase or dilute that of the 
channel. It will suffice in the present connection to note that 
production is less in the backwaters than in the channel in 
only 48, or 26 per cent., of the 185 monthly averages—the total 
number of all of the monthly averages of all stations but the 
Illinois and Spoon rivers. In Quiver Lake we find 30 months 
out of 53, or 57 per cent., deficient in production as compared 
with the channel; in Dogtish Lake, 6 out of 25, or 24 per cent.; 
in Flag Lake, 2 out of 24, or 8 per cent.; in Thompson’s Lake, 8 
out of 52, or 15 per cent.; and in Phelps Lake, 2 out of 31, or 6 
per cent. 
Lakes most free from access of tributary water and from 
vegetation are most constant in their excess of production over 
channel waters. Thus we find that of these 48 instances of 
deficient production in the backwaters 30 occur in Quiver 
