542 Wisconsin Academy of Sciences , Arts, and Letters. 
OCONOMOWOC LAKE. 
A complete set of observations was made on this lake in Aug¬ 
ust, 1900, a day and a night series in October, and a complete 
set in June, 1901. The lake was poor in phytoplankton. 
Daphnia hyalina. —In August, young of this species were 
rare in the upper five meters in the daytime and adults were at 
a depth of seven meters. The former appeared at the surface 
during the second half hour after sunset and adults half an 
hour later. Yo adults were at the surface an hour and a half 
before sunrise and the young left the surface during the second 
half hour before sunrise. Only young were found in the Oc¬ 
tober catches. They were at a depth of five meters in the day¬ 
time but were found at the surface two hours after sunset. 
In June, only adults were found. They were at a, depth of 
two meters in the daytime but came to the surface about an, 
hour and a half after sunset and were not found in the surface 
catch made two and a. half hours before sunrise. 
Daphnia pulicaria. —Young were at a depth of six meters 
and adults ten meters in the day catches of August. The for¬ 
mer came to the surface about half an hour after sunset and 
adults half an hour later. Yeither young nor adults were 
found in the surface catch made an hour and a half before sun¬ 
rise. Adults only were found in October. They were at a 
depth of twelve meters in the daytime but were taken in a sur¬ 
face catch made two hours after sunset. 
In June, both young and adults were found at a depth of 
only one meter in the daytime. The former came to the sur¬ 
face during the first half hour after sunset and adults half an 
hour later. Both left the surface during the second half hour 
before sunrise. 
Diaphanosoma brachyurum. —There was no diurnal move¬ 
ment of this form. 
Leptodora Jiyalina. —Only the young of this species were 
found in August. They were not present in the surface catch 
made two hours after sunset but were in some of the morning 
surface catches. They left the surface during the second half 
hour before sunrise. Leptodora was not found in June. 
Bosmina. —There was no diurnal movement of Bosmina. 
Chydorus. —This form! was not found in August and Octo¬ 
ber. In June, it was rare but showed no diurnal movement. 
