Juday—Diurnal Movement of Plankton Crustacea. 549 
Diaphanosoma brachyurum. —There was no diurnal move¬ 
ment of this species. 
Leptodora Lyalina. —This species was found in October, 
May, and June. It was found in only one of the six day series 
of these three months and that was October 25, in the catch 
made at a depth of six meters. Birge (2b, p. 405) found the 
movement of this form to be less than three meters in extent. 
In October, young came to the surface during the first half 
hour after sunset on the 5th and adults; half an hour later. 
Young appeared at the surface during the second half hour 1 be¬ 
fore sunset on the 8th and adults during the first half hour 
after sunset. In the morning series of the 12th, adults left 
the surface during the third half hour before sunrise and 
young were still present in the surface catch made just at sun¬ 
rise. 
In May, Leptodora came to the surface during the fourth 
half hour after sunset in an evening series and left, the surface 
during the third half hour before sunrise in a morning series. 
It was not found in the other evening and morning observa¬ 
tions. 
In June, adults appeared at the surface about half an hour 
after sunset on the 3rd and young had not yet appeared half an 
hour later. On the 11th, young came to the surface about an 
hour after sunset and adults had not yet appeared as late as an 
hour and a half after sunset. In the morning series of the 
12th, neither young nor adults were found as early as two and 
a half hours before sunrise. Adults came to the surface during 
the third half hour after sunset on the 24th but no young were 
found as late as an hour and a half after sunset. In the morn¬ 
ing catches of the 25th, adults left, the surface during the sec¬ 
ond half hour before sunrise and young about sunrise. 
Bosmina. —This form 1 was found in June but there was no 
diurnal movement. 
Chydorus. —There was no movement of this form. 
Epischura lacustris.—Epischura was not found in any of 
the day catches' but was present in the evening, night, and morn¬ 
ing catches of October and June. In October, it appeared at 
the surface about half an hour after sunset on the 8th. On 
the 12th, it left the surface about two hours before sunrise. In 
June, this species came to the surface during the second half 
hour after sunset in both of the evening series. In the morn- 
