4 Wisconsin Academy of Sciences, Arts and Letters. 
ever, that a large amount of oxygen was present when the ani¬ 
mals entered the resting stage. The following table shows the 
facts: 
1906. 
Depth, m. 
Temp., C. 
0, cc. per 1. 
Remarks. 
May 22. 
22 
9.6° 
5.2 
No cocoons. 
May 29. 
22 
9.6° 
4.7 
No cocoons. 
June 2. 
22 
9.9° 
4.0 
Abundant cocoons. 
June 8. 
22 
10.1° 
3.0 
Abundant cocoons. 
It appears that there was as much as four cubic centimeters 
of oxygen per liter when the cocoons were formed. This is a 
smaller amount than the surface water contained, as this held 
from six to seven cubic centimeters per liter. This Survey 
has found, however, that the genus Cyclops is by no means 
sensitive to a decline in oxygen under the ordinary conditions 
found in lakes, and that it can live in large numbers in water 
which contains 0.5 cubic centimeters or more of oxygen. These 
observations do not apply directly to C. bicuspidatus , but it is 
hardly probable that this species differs widely in this respect 
from its nearest allies. It does not seem probable that the rise 
of temperature in the lower water determines directly the time 
of pupation. It will be seen from the table that during the 
period in which the change took place the temperature rose 
from 9.6° to 10.1°—a change of only 0.5°. 
The hatching in the autumn begins and seems to be almost 
completed before the oxygen reaches the bottom water in ap¬ 
preciable quantities and while the temperature of the bottom 
water is not changing greatly and is decidedly higher than it 
was in June. This will appear from the following table: 
1906. 
Depth, m. 
Cc. O per 1. 
Depth at 
which O 
disappeared. 
Temp, at 
bottom. 
Sept. 26. 
22 
0.0 
15 m. 
12.2° 
Sept. 29. 
22 
0.0 
14.5 m. 
12.7° 
Oct. 6. 
22 
0.0 
17 m. 
12.8° 
Oct. 8.. 
22 
0.0 
14 m. 
13.0° 
Oct. 11. 
22 
5.5 
13.8° 
