Juday—Diurnal Movement of Plankton Crustacea. 535 
LOCATION OF THE LAKES. 
Observations were made on thirty of the lakes of southeast¬ 
ern Wisconsin. Twenty-five of these lakes lie in two groups, 
fifteen belong to The Chain o’ Lakes in Waupaca County and 
ten belong to the Oconomowoc-Waukesha lakes in Waukesha 
County. The five lakes not included in these two groups are 
Mendota, Geneva, Green, Big Cedar, and Elkhart. Only ten 
of these thirty lakes, however, were studied with special refer¬ 
ence to diurnal movement: Beasley and Rainbow of The 
Chain o’ Lakes, Okauchee, Oconomowoc, Nagawicka, and Pe- 
waukee of the Oconomowoc-Waukesha lakes; and all the in¬ 
dividual lakes named above except Elkhart. 
The physical features of these lakes have been fully discussed 
by Fenneman (5) in Bulletin No. 8 of the Wisconsin Geolog¬ 
ical and Natural History Survey, so that little need be said here 
on that point. Suffice it to say that these, ten lakes represent 
various physical, as well as biological conditions. They differ 
widely in area, the largest lake having over seven hundred times 
the area of the smallest. The maximum depth ranges from, a 
little less than fourteen meters in Pewaukee lake to seventy-two 
meters in Green lake, but it is less than thirty meters in seven 
of the ten lakes. 
There was also a very marked difference in the amount of 
aquatic vegetation found in the lakes. 
APPARATUS AND METHODS. 
The pump method was used in making the catches. A num¬ 
ber three clock pump and garden hose with a diameter of two 
and a half centimeters, were used. A quantity of water, ten 
to fifteen liters, was pumped from each depth and strained 
through, a plankton net whose straining cone was made of Du- 
four’s No. 20 bolting cloth. During the process of straining, 
the net was: submerged so that the stream of water from- the 
pump would not strike the bolting cloth directly. 
A complete set of observations consisted of four series : a 
day, an evening, a night, and a morning series. These were 
made during clear weather, with the exception of one day 
series, and at a time when the surface water was disturbed as 
little as possible by waves. The day and night catches were 
made at intervals of one to three meters and they covered the 
