16 Illinois State Laboratory of Natural History. 



rests when placed in position. The plankton bucket, with its'- 

 method of attachment to the net, is similar to that described 

 for the vertical net. 



3. The Method of Operating the Pump. — The pump is 

 carried in a suitable row-boat, and the suction hose is operated 

 from the stern by one person while a second attends to the 

 pump and the net (Plate VI.). In the choice of a location 

 and in the position of the boat, due regard must be had to the 

 direction of the wind and the current, if any, so that no fil- 

 tered water may reenter the pump. In our work in the lakes it 

 has been our custom to tie the boat to poles set for this 

 purpose ; but in the river the boat has been allowed to drift 

 with the current in order to make the collection, so far as may 

 be, from the same body of water. After the depth is ascer- 

 tained the suction hose is lowered to within a foot of the 

 bottom, the pump is thoroughly rinsed, and while still filled 

 with bottom water the discharge hose is connected with the 

 net. As the pumping progresses the funnel is raised at regu- 

 lar intervals ; for example, every tenth stroke, the interval and 

 the distance raised varying, however, with the total depth of 

 the water to be traversed. Since the pump is filled with 

 bottom water when pumping begins, it is necessary to shorten 

 the first interval by the number of strokes required to fill the 

 pump and to correspondingly lengthen the last one. In this 

 manner a vertical column of water of the desired volume may 

 be pumped through the net. In addition to the vertical catch we 

 have followed the custom of making one from bottom water and 

 another from surface water. After the requisite number of 

 strokes of the pump have been made the hose is disconnected 

 and the net removed from the frame and thoroughly rinsed 

 down. The catch is concentrated in the bucket and trans- 

 ferred to the bottle of alcohol or formalin. 



The pumping method has been successfully employed in 

 freezing weather by attaching a foot- warmer to the side of the 

 pump and encasing the whole in a wrapping of felt paper. 

 The foot-warmer burns a cake of specially prepared coal, and 

 will keep the pump warm during a day's work of ten hours. 

 A special drain-cock (not shown in Plate Y.) provides for the' 



