403 



if properly handled. The depth at which the net moves can then be regu- 

 lated by the rale at which it is drawn through the water. 



The only difficulty experienced in operating this net was that the 

 ring carried the open end under at once, thus catching enough air in the 

 net to float it. To obviate this difficulty, a 25x80 mm. glass shell partially 

 filled with water was fastened to the apex of the net by means of a cork 

 stopper. This carried the net under at once, and when the catch was made, 

 the cork was loosened and the collection dropped into the bottle. 



For quantitative work, on such plankton as was present, the following 

 variation of the pumping method was used: The whole apparatus had to 

 be light enough to be portable. Some difficulty was experienced in getting 

 a satisfactory pump. The pump used is known in the trade as the Barnes 

 hydroject pump, manufactured by Barnes Mfg. Co., Mansfield, Ohio. It has 

 a brass cylinder and throws one-fourth liter per stroke. Its general appear- 

 ance is shown in Fig 4. To this was attached a net of bolting silk (Du- 

 four No. 20) and a detachable bucket. (Windows covered with wire cloth. 

 200 meshes to the inch.) A three-quarter inch hose (inside measurement) 

 was used. The end was closed with a cork and an opening made in the 

 side of the hose just above the cork, so that the water from a given level 

 might be secured with greater accuracy. The end of the hose was fastened 

 to a float, so that the collection could be taken from any depth desired. 

 By means of a rope and pulley, this float could be placed at any point in the 

 pond. 



Material was killed in a 4% solution of formalin. All organisms were 

 counted in every collection except two. In investigating a small area, I 

 believe that greater accuracy is secured by filtering a small amount of 

 water and counting all the oragnisms than by filtering a large amount and 

 counting a fraction of it. The amount counted in either case must be large 

 enough to include samples of all the organisms present. 



The source of error in the first case is the uneven distribution of organ- 

 isms at a given level. In the second case, the error is due to the difficulty 

 of thoroughly mixing organisms having a different specific gravity. 



The soundings were taken when the pond was covered with ice. The 

 ice was ruled at ten-foot intervals, holes bored at the intersections, depth 

 measured through these openings and entered on the map of the pond. A 

 guage was set December 21, 1909. From the readings of the gauge, the 

 depth at any point at any time could be determined. 



