584 Wisconsin Academy of Sciences , Arts , and Letters . 
ascertaining its food value. In order to secure enough ma¬ 
terial for such studies it is necessary to centrifuge from 1,000 
to 1,500 liters of water and this requires an apparatus that 
will act continuously in separating the nannoplankton from 
this large quantity of water. For this work a De Laval 
clarifier and filter, belt style, A size, is used, in which the 
water is first centrifuged and then filtered. Fig. 7 is a sketch 
drawing, showing the equipment of the laboratory that is 
used in making these investigations. C is the clarifier-filter 
or centrifuge; M is the electric motor by which the centri¬ 
fuge is driven through an intermediate; T is the tank into 
which the water is pumped from the dock by a pump marked 
P in the figure. 
The sample of water is obtained from a regular station 
situated in the deepest portion of Lake Mendota and it con¬ 
sists of a certain quantity of water pumped from each meter 
between the surface and 20 meters, with the exception of 19 
meters. The vane pumps described on p. 508 are used in 
procuring the sample. The water is strained through the 
large plankton net and it is caught in containers (milk cans) 
as it flows from the large can in which the net is suspended. 
It is then conveyed by launch to the laboratory dock where 
it is pumped into the tank. The launch carrying about 500 
liters of water and the pumping apparatus is shown at the 
dock in Plate XXXVII, fig. 1. 
The tank is made of galvanized iron and has a capacity of 
about 1,200 liters. It is mounted on a framework which 
rests on a platform scale so that the quantity of water used 
for a sample is readily ascertained by weighing. With the scale 
one can also readily ascertain the fate at which the sample 
is being centrifuged. The framework elevates the tank to 
such a height above the centrifuge that the water readily 
flows from the forfner to the latter through a hose, the rate 
of flow being regulated by a valve. 
A sectional view of the bowl of the centrifuge is shown in 
Plate XXXVII, fig. 2. The water enters at A and passes down 
to the bottom of the clarifying compartment B where some of 
the material is deposited. Then it passes out to the peri¬ 
phery of this compartment, C, where the centrifugal force 
is at a maximum. By far the greater portion of the material 
is deposited here. The water next flows upward and toward 
