Juday■—Diurnal Movement of Plankton Crustacea. 537 
In. stating the time at which the various forms reached the 
surface in the evening and left it in the morning, the exact hour 
of the day is not given. The time is reckoned in; half hours 
with respect to the time of sunset and sunrise. This is done 
because the time of the movement is closely related to the time 
of sunset and sunrise and this latter time is constantly chang¬ 
ing with respect to the hours of the day. 
The following results are given in, considerable detail for 
each lake in order to indicate whatever change there may be in 
the movement of any form at different times in the same lake. 
Then: the results are given for each form for all the lakes in 
which it is found, so as to show the differences in the move¬ 
ment of the same form in different lakes. 
BEASLEY LAKE. 
The observations on this lake consisted of a day and a night 
series the last of July and a complete set of observations early 
in September, 1900. The lake was comparatively poor in 
phytoplankton. 
Daphnia hyalind. —In July, young were found at the surface 
during the day and adults at a depth of one meter. In the 
flight catch made an hour and three quarters after sunset, adults 
were very numerous at the surface, apparently indicating the 
presence of a “swarm.” 
In September, the' day position of both young and adults was 
the same as in July. Adults appeared at the surface during 
the second half hour after sunset and disappeared about half 
an hour before sunrise. 
Diaptomus. —In July, both young and adults were absent 
from the upper four meters in the daytime but both were found 
at the surface an hour and three-quarters after sunset. 
Only adults were found in September. They were at a 
depth of one meter during the day. They appeared at the: sur¬ 
face during the' first half hour after sunset and were not found 
in the surface catch made' nearly two hours before; sunrise. 
Cyclops. —This form did not show any diurnal movement 
either in July or September. 
Nauplii. —There was no diurnal movement of the nauplii. 
Corethra larvae.—In the day catches of July they were not 
found above a depth of eight meters but were- found at a depth 
