Juday—Diurnal Movement of Plankton Crustacea. 543 
Epischura lacustris. —This species was not taken in the day 
catches in August but it appeared at the surface during the first 
half hour after sunset and disappeared during the second half 
hour before sunrise. It was not found in October. 
In June, it was found at the surface only in the morning 
catches and it disappeared during the second half hour before 
sunrise. 
Diaptomus. —In August, young were at the surface and 
adults at a depth of two meters in the daytime. The latter ap¬ 
peared at the surface about sunset and left the surface again 
about sunrise. There was no diurnal movement in October 
and June. 
Cyclops and nauplii. —There was no diurnal movement of 
these forms. 
Corethra larvae.—In August, Coretkra larvae were not found 
in the upper eight meters in the daytime but were at five meters 
in the night catches. In October, they were at a depth of four¬ 
teen meters in the daytime but were at three meters at night. 
Only one individual was found in all the catches made in June. 
NAGAWICKA LAKE. 
Two complete sets of observations were made on this lake, 
one in August, 1900 and another in June, 1901. Phytoplank¬ 
ton was rather abundant. 
Daphnia hyalina. —Two varieties of this species were pres¬ 
ent. Those with round and those with pointed helmets were 
found in August but only the former in June. In August, the 
young of the round helmeted variety were at a depth of six 
meters and adults at three meters in the daytime. The for¬ 
mer appeared at the surface about sunset and adults during the 
second half hour after sunset, ]STo adults were found at the 
surface one and a half hours before sunrise and the young left 
the surface during the third half hour before sunrise. 
In June, young were at the surface and adults at one meter 
in the daytime. The latter appeared at the surface during the 
second half hour before sunset and disappeared again about 
sunrise. 
Young with pointed helmets were at the surface and adults 
at one meter in the daytime in August, The latter came to the 
surface during the first half hour after sunset and were not 
