THE DIURNAL MOVEMENT OF PLANKTON 
CRUSTACEA. 
CHANCEY JUDAY. 
INTRODUCTION. 
The following paper on the diurnal movement of plankton 
Crustacea is based upon observations made for the Wisconsin 
Geological and Natural History Survey between JulyjL, 1900 
and June 30, 1901. The work was planned to continue for a 
longer period but it became necessary to discontinue it at the 
end of a year. This left the work in a rather unsatisfactory 
condition for it had scarcely passed the experimental stage. As 
a result, this report is preliminary in nature but it is written 
with the hope that it may contain helpful suggestions for future 
work along this line. 
Enough, however, was accomplished during the year to show 
that diurnal movement is not a simple, unchangeable phenome¬ 
non which may be determined for the various crustacean forms 
of a, lake by a single set of observations. On the contrary, the 
results show not only that the movement of a single species is 
not the same in all the lakes in which it is found but also that 
the movement of a species may change from time to time in the 
same lake. To determine the extent and nature of these 
changes, iti would be necessary to make regular observations on 
a lake covering the period from early spring till late fall. Such 
a study would contribute much, m> doubt, to a better under¬ 
standing of the factors instrumental in the production and 
modification of diurnal movement. 
I wish to acknowledge my indebtedness to Dr. El. A. Birge, 
Director of the Survey, for the plan of the work, as well as for 
his direction and helpful counsel during its progress. 
