The Coefficient of the Dredge. 
285 
of Crustacea had been selected, or if the total of all the Crusta¬ 
cea had been chosen. 
There is still a third question relating to the coefficient to 
the dredge, namely, does the net function similarly on different 
occasions, or does its coefficient vary irregularly and in such a 
way as to vitiate conclusions based on the hauls of the net? 
This question is partially answered by the determination of the 
dredge coefficient, as shown in Table I. A second answer can 
also be given. During the winter the numbers of Daphnia and 
Diaptomus do not increase by reproduction, and the successive 
catches should therefore show no very great variation. In a sub¬ 
sequent section, dealing with the question of swarms, I have 
given the figures for the catches of these genera during the 
winter of 1895, from which it appears that the variation in suc¬ 
cessive catches made within a short time of each other is no 
greater than may be found between catches made on the same 
day. Still further, a diagram is given (Fig. 21), showing the 
numbers of Cyclops caught during the year 1895. This diagram 
shows plainly that when the average number of Cyclops is ap¬ 
proximately constant, the individual catches do not ordinarily 
vary greatly from the average, no more than would be expected 
from Cyclops ’ necessarily somewhat irregular distribution in the 
lake. An examination of the maximum and minimum catches 
in the tables for the different species shows the same result. 
I do not pretend that I have determined the coefficient of my 
nets with absolute accuracy, nor that the coefficient of the net 
is exactly the same on different occasions; but the careful study 
whose results are summarized above has convinced me that the 
coefficient of the net is quite as constant as any of the factors 
entering into the determination of the plankton. The number 
of the Crustacea certainly varies from point to point in the lake. 
Where a fraction only of the Crustacea are counted, the deter¬ 
mination of the number caught is an approximation and is sub¬ 
ject to error. This error, is, of course, multiplied greatly in 
stating the number of Crustacea in terms of square meter of 
surface. Among the variables and approximations which en¬ 
ter into the statement of the results of plankton work, I think 
it may fairly be said that the coefficient of the net is one of the 
