114 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
and distribution of the minute floating organisms comprehended 
under the general name of plankton, for it is on these that all the 
fishes and other large forms are ultimately dependent for their food 
supply. Besides the mere determination of the species of animals 
and plants which comprise the plankton, if is desirable to ascertain, 
by means of specially devised apparatus, its volume and its vertical 
distribution. Since 1898, Professor Reighard, in association with 
Prof. H. B. Ward, had been at work on a net which would register 
automatically the volume of water from which a given amount of 
plankton had been abstracted; and this subject was continued in 1900. 
During the summer of 1899, it had become evident that, in order to 
determine the amount of water passing through a plankton net when 
in use in the lake, it would be first necessary to ‘‘rate” in a labora- 
tory the meter placed in the net opening for the purpose of indicating 
the rate of flow of the water through the opening. It was required 
to measure the volume of water passing through the net opening at 
different net velocities in a unit of time, and to determine the number 
of revolutions of the meter corresponding to such volume for each 
velocity. This could be done only in a hydraulic laboratory, and 
after investigation it was decided to make use of the facilities of the 
hydraulic¢ laboratory of the Ohio University at Columbus, Ohio. The 
Commission had the services of Prof. William T. Magruder, of the 
Columbus laboratory, and the rating was carried out under the joint 
direction of Professor Magruder and Professor Ward. 
The work of practically testing the efficiency of plankton nets was 
then transferred to Put-in Bay. Here four nets were constructed of 
bolting cloth of four different degrees of fineness. Each of these nets 
was then hauled repeatedly in the open lake from the steamer Shear- 
water, and about seven hundred such hauls were made. The auto- 
matic record of each haul showed the time occupied by the haul 
(recorded in fifths of a second) and the number of revolutions of the 
meter during the haul. From the curve constructed from the labora- 
tory tests it was possible to determine the amount of water filtered by 
each net during the entire haul, as well as during each fraction of the 
haul. The results so far obtained may be stated as follows: 
1. All of the nets experimented upon become clogged during the haul, so that 
they filter less water toward the end of the haul than at its beginning. This clog- 
ging is so serious as to make it donbtful whether such nets can be, in any way, 
made to yield quantitative results of value. 
2. The records show that the pitching of the boat affects the amount of water 
passing through the net, a downward motion of the boat decreasing the amount 
and an upward movement increasing it. 
3. The records show that currents in the water or the drifting of the boat 
noticeably increase the amount of water passing through the net. 
+. It was rendered probable that the nets filter a much larger part of the water 
through which they are drawn than the work of Hensen has indicated. 
This work yields the first direct measurement of the water passing 
through a plankton net, and when completed will show under what 
conditions, if at all, such nets may be used. The conclusions stated 
