A SUMMER RESTING STAGE IN THE DEVELOPMENT 
OF CYCLOPS BICUSPIDATUS CLAUS. 
E. A. BIRGE AND C. JUDAY. 
[Biological Notes from the Laboratory of the Wisconsin Geological and Natural 
History Survey. I.] 
In examining some mud from the bottom of Lake Mendota, 
brought into the laboratory of the Survey in the fall of 1905, 
a small oval body was found, whose exterior was composed of 
particles of the mud and in whose interior we expected to find 
a winter egg or similar resting stage of some animal. Dissec¬ 
tion showed, however, that the cocoon contained a well devel¬ 
oped, though sexually immature Cyclops , and further study 
showed that the mud held a great number of these cocoons, from 
which the Cyclops soon hatched out in the laboratory. During 
the season of 1906, the history of this peculiar resting stage 
was investigated as closely as circumstances permitted, with the 
results which are given in the following paper. 
The annual development of the genus Cyclops in Lake Men- 
dota was described in a paper published in 1897, and is in brief 
as follows (Birge, ’97, pp. 326-335) : In April of each year 
the spring development of Cyclops begins and the numbers rise 
rapidly to a maximum. In 1895, the maximum was during 
the month of May, when the average number per square meter 
of surface was over 900,000. In 1896, the maximum extended 
from the middle of April to the middle of May, with an aver¬ 
age of over 1,400,000 per square meter of surface. This enor¬ 
mous number of animals is chiefly composed of immature in¬ 
dividuals, very few of them reaching sexual maturity. At the 
period of maximum development they are distributed pretty 
