-538 Wisconsin Academy of Sciences, Arts, and Letters. 
of only four meters at night. In September, their day and 
night positions were practically the same. 
RAINBOW LAKE. 
A day, a night, and an early morning series were made late 
in July and a complete set of observations early in September, 
1900. Comparatively little phytoplankton was found on both 
occasions. 
Daphnia hyalina. —Two varieties of this form were found. 
One variety had round helmets and the other had rather long, 
pointed helmets. The former remained in the region of the 
thermocline both day and night in July and also in September. 
Young of the variety having pointed helmets were found at 
the surface in the day catches of July and adults at a depth of 
two meters. The latter were present in the surface catch made 
two and a half hours after sunset. 
In September, young were not found in the upper four 
meters and adults not in the upper six meters in the day 
catches. Both appeared at the surface during the second half 
hour after sunset and both left the surface about one hour 
before sunrise. 
Daphnia retrocurva. —Adults were absent from the upper 
two meters in the daytime in July but were present in the sur¬ 
face catch at night. They were at a depth of six meters in the 
daytime in September. They came to the 1 surface a little more 
than an hour after sunset and were not found at the surface 
two hours before sunrise. Young were not noted in either 
month. 
Ceriodaphnia. —This forms was rare both in July and Septem¬ 
ber but showed no diurnal movement. 
Diaphanosama hrachyurum. —Young and adults were not 
found above a depth of five meters in the day catches of July 
but both were at the surface at night. In September, young 
were at the surface and adults at a, depth of two meters in the 
day catches. The latter appeared at the surface during the 
first half hour after sunset and disappeared again during the 
second half hour before sunrise. 
Leptodora hyalina. —In July, this form was not found in the 
upper nine meters in the daytime but was taken at a depth of 
only one meter at night. The September day and night posi¬ 
tions were six and four meters respectively. 
