540 'Wisconsin Academy of Sciences, Arts, and Letters. 
OKAUCIIEE LAKE. 
A complete set of observations was made on this lake in 
August, 1900, a day and a night series in October, and a com¬ 
plete set in June, 1901. The phytoplankton was rather abun¬ 
dant. 
Daphnia hyalina. —Two varieties of this form were found in 
August and October, those with round and those with pointed 
helmets. Only the round helmeted ones occurred in June. 
Young of the round helmeted variety were found a,t the sur¬ 
face and adults at a depth of two meters in the day catches of 
August. The latter appeared at the surface during the second 
half hour after sunset and disappeared during the second half 
hour before sunrise. Young were at the surface in Octo¬ 
ber and adults at a depth of one meter. The- latter were pres¬ 
ent in the surface catch at night. In June, both young and 
adults were at a depth of one meter in the daytime. The for¬ 
mer reached the surface about half an hour before sunset and 
the latter about sunset. Both disappeared from the surface 
about sunrise. 
The variety with pointed helmets did not show diurnal move¬ 
ment. 
Daphnia retrocurva. —This species was found in August and 
October but not in June. There was no diurnal movement. 
Daphnia pulicaria. —In August^ young were found at a 
depth of eight meters and adults at nine meters in the daytime. 
Two and a. quarter hours after sunset young were found at a 
depth of only two meters and adults four meters. 
In October, young were at a depth of six and adults twelve 
meters in the daytime. Three and a quarter hours after sunset 
the former were, at the surface and the latter at two meters. 
In June, the day catches showed young at a depth of one meter 
and adults at three meters. The former appeared at the sur¬ 
face about half an hour before sunset and the latter about two 
hours after sunset. Both disappeared from the surface during 
the fifth half hour before sunrise. 
Daphnia longiremis. —This species remained in the region 
below the thermocline or below twelve' meters, both day and 
night during these observations. It was most abundant within 
two or three meters of the bottom. About the middle of No¬ 
vember, however, after the disappearance of the thermocline, it 
was found at a depth, of only two meters on a cloudy day. 
