OUTLINE OF STUDY. 9 



the conclusions reached by Reighard (Reighard '98) that it is 

 very doubtful if the pump gives one a representative collection 

 of a column of water. In deep waters, of course, the pump in- 

 volves very unwieldy apparatus. In shallow waters, especially 

 for making collections at specific levels, the pump is a useful 

 adjunct to plankton apparatus. In the opinion of the author 

 no method has yet been devised that serves the purpose so well 

 as a vertical net. It is very much to be desired that the net 

 should have a wide opening, as is stated by Reighard. Port- 

 ability was so necessary in my case, however, that size had to be 

 sacrificed. The undoubted fact that nets vary in their collect- 

 ing ability because of the clogging of the meshes, especially in 

 silt laden waters, was deemed in these researches as of minor 

 importance, partly because the waters examined were for the 

 most part fairly clear, and partly because, as will be seen later, 

 the author attaches very little importance to exact measure- 

 ments of the plankton, but relies for results on averages. 



The net used was of the pattern of Hensen, the upper cone 

 being of copper, with an opening 10.5 cm. in diameter. The 

 net was of bolting silk, attached below to a removable bucket, 

 of a form devised by Professor Birge. The net was drawn 

 from the bottom to the surface, the net washed down from the 

 outside, and the bucket, by the aid of a wash bottle filled with 

 alcohol, emptied directly into the collecting bottle. I made it 

 a rule to make three collections at each station, and in stating 

 results the three collections were averaged. 



To determine the gross amount of plankton it was decided to 

 use the centrifuge. The objections to the method of settling 

 in graduated tubes have been well stated by other authors. 

 (Ward '95, Kofoid '97.) The lack of exactness in plankton 

 measurements does not warrant the labor of the gravimetric 

 method. It was decided to use the centrifuge, as being the 

 best method yet devised. For this purpose the ordinary uri- 

 nary centrifuge was used, with tubes graduated to tenths of a 

 centimeter. After a little experience it was decided to ran 

 the centrifuge in the following way: 1st, two revolutions of 

 the crank ; 2nd, two revolutions in the reverse direction ; 3rd, a 



