536 Wisconsin Academy of Sciences, Arts f and Letters. 
entire depth of each lake with the exception of Green lake. The 
day catches were made not earlier than three hours, after sun¬ 
rise and, with one exception, not later than three hours before 
sunset; the night catches, two to three hours after sunset. 
The evening and morning catches extended to a, depth of two 
to eight meters. They were made at half hour intervals and 
usually covered the period from about half an: hour before sun¬ 
set to two hours after sunset. Some observations, however, 
were begun as early a,s an hour and a. half before sunset. The 
morning series were begun an hour and a half to three 1 hours 
before sunrise and continued until sunrise., or sometimes an 
hour' after sunrise. The purpose of these observations was to 
determine approximately the. time at which the various forms 
showing diurnal movement, reached the surface in the evening 
and left it- in the morning. 
The depth of all the surface catches varied from about three 
centimeters, when the water was calm, to. seven or eight centi¬ 
meters when it was disturbed by waves. 
The time was too. limited to permit a count of the smaller 
forms for nearly nine hundred catches were made during the 
year. So each catch was examined under the low power of a 
microscope and the relative number of individuals of each of 
the smaller forms was indicated by the five terms, absent, rare, 
few, many, or abundant. The larger 1 forms were counted. The 
results for each form in the day catches and in the night catches 
were then tabulated in parallel columns so that the depth to 
which diurnal movement affected the. day distribution could be 
determined readily. In making these comparisons, however, 
one must constantly remember the fact that two catches from 
the same depth and separated by only a brief interval of time, 
may show a considerable, difference in the number of crusta¬ 
ceans. Therefore, unless the difference between a day catch 
and a night catch at the. same depth was great enough to exclude 
all doubt, it was counted as no change.. But at and near the 
surface, there, was little danger of a mistake, especially in those 
forms which were absent from this region in the. day time but 
occupied it at night. 
Separate but similar tabulations were made, for the evening 
and morning catches. Some of the genera represented, such as 
Diaptomus and Cyclops, were tabulated as a whole and not sep¬ 
arated into species. 
