1896.] 



NATURAL SCIENCES OP PHILADELPHIA. 



281 



The receptacles having been filled with the water to be examined, 

 are caused to revolve for one or two nnnutes, when the entire con- 

 tents of suspended matter in the water is thrown down to the bottom 

 of the tube, from which the volume may be read off by means of the 



graduated scale on the outside of the tube. The plankton thus ex- 

 peditiously secured can be transferred quickly to a vial or other re- 

 ceptacle, to be weighed or otherwise examined at leisure. 



The apparatus is simple and efficient, covering, I think, some of 

 the faults in the Hensen method, as pointed out by Haeckel, at any 

 rate supplementing the counting method by one which makes it 

 possible to secure a far greater number of estimations in a given time. 

 It is free from many sources of error connected with the use of a net, 

 and for the practical purposes of oyster and fish culture enables the 

 scientist in charge to ascertain the diurnal variations of any given 

 area of water, from planktonic standards previously established 

 under the most favorable conditions. I have chosen the name 

 planktonokrit for this apparatus, and I am confident that it will 

 facilitate in many ways the solution of the oecological problems 

 which confront the student of aquatic organisms, and at any rate 

 free him, to a certain extent, from " the Danaides task " of counting 

 the individuals. 19 



