19 
tips of the elbows before it returns to the axis for discharge at 
the lower end. This machine is geared to give, with power, 
8,000 revolutions per minute. When fitted with cranks for two 
men, four to five thousand revolutions can be obtained. This 
apparatus was tested with water from the river at a time when 
it was full of water bloom,—formed principally of Carteria,— 
and also with water from the lakes in varying kinds and amounts 
of plankton. It proved to be more effective in the removal of 
the plankton than any method previously tried, but the opera- 
tion of the machine. by hand was extremely laborious, and the 
precipitation of the plankton was very slow. Furthermore, a 
variable and oftentimes considerable amount of the plankton— 
especially that found in the water-bloom—is at times lighter 
than the water, and thus cannot be removed by centrifugal force 
with the heavier constituents. 
In November, 1897, a Berkefeld army filter (system 
Bruckner) was added to the plankton equipment. It is very 
efficient in removing all the solid matter from the water, and its 
operation with ordinary samples is quite rapid. It consists of 
a force-pump and a cylinder of diatomaceous earth, upon which 
the plankton and silt contained in the water are collected. This 
is removed by washing with a brush, but in the process a 
part of the substance of the cylinder is brushed off. This 
debris is added to the silt of the water and renders subsequent 
microscopic examination more difficult. The brushing is also 
disastrous to some of the more delicate organisms, but leaves 
by far the greater part of the minute forms which escape the 
silt intact and in suitable condition for enumeration, 
During the past two years some progress has been made 
with an examination, measurement, and enumeration of the 
plankton of the regular series, though much of the time has 
been given to the preparation of plankton apparatus and the 
improvemeit of the method. In this work the examination of 
the test collections by the enumeration method has been par- 
ticularly time-consuming. The work of enumeration has been 
facilitated by the use of a set of six counting machines, which 
enable the observer to keep a record of six different species at 
once without the mental effort of carrying the count in the mind. 
An extended amount of this work remains to be done before we 
