Juday—Diurnal Movement of Plankton Crustacea. 539 
Bosmina .—This form was rare and no diurnal movement 
was apparent. 
Holopedium gibberum .—In July, this species was found in 
the region of the thermocline but there was no movement. It 
was not found in September. 
Epischura lacustris .—In July, this form was at a depth of 
two meters in the day catches but was present in the surface 
catch at night. It was not above four meters in the daytime 
in September but appeared at the surface near the end of the 
first half hour after sunset and was not found in the surface 
catch made an hour and a half before sunrise'. 
Diaptornus .—Young were at the surface and adults at a 
depth of one meter in the day catches of July. The latter 
came to the surface at night. In September, adults were at a 
depth of two meters in the daytime. They reached the surface 
during the first half hour after sunset and left the surface again 
during the second half hour before sunrise. 
Cyclopsnauplii, and Corethra larvae.—Yo diurnal move¬ 
ment was shown by these forms in either month. 
BIG CEDAK BAKE. 
The observation on this lake consisted of a day and a night 
series made on August 1, 1900. 
Daphnia hyalina .—This form was not found in the upper 
three meters in the day catches but it was present in the surface 
catch at night. 
Ceriodaphnia .—This form was rare and showed no diurnal 
movement. 
Diaphanosoma braehyurum .—The day and night positions of 
this species were the same. 
Bosmina .—This form was rare and showed no diurnal move¬ 
ment. 
Epischura lacustHs .—This species was found at a depth of 
four meters in the day time but it was present in the surface 
catch at night. 
Diaptornus .—Both young and adults of this form were found 
at a depth of four meters in the day time but both came to the 
surface at night. 
Cyclops .—The young of this genus were found at the sur¬ 
face in the day catches but the adults were at a depth of four 
meters. The latter came to the surface at night. 
