METHODS. 



The collections were preserved in bottles of uniform capacity 

 (60 cm. 3 ), in alcohol-formalin mixture (2 per cent, formalin in 70 

 per cent, alcohol), and after measurement by the centrifuge were 

 released from the compressed condition in the measuring tubes and 

 returned to the containers. 



The counting was done by a modified Sedgwick-Rafter method 

 (see Kofoid, '97), in which 1 cm. 3 of a suitably diluted plankton is 

 distributed evenly in a cell 20 X 50 mm. The plankton was diluted 

 or condensed (from 60 cm. 3 of fluid) according to the quantity of 

 plankton and the amount and nature of the silt. Larger organisms 

 such as the Entomostraca were counted in the whole catch, or in 

 larger collections in Yio to 1 / 50 of the total catch ; and the smaller 

 organisms in l l^ to V^o- The filter-paper catches which supple- 

 mented those of the plankton net from August 3, 1896, to the end 

 of the series, March 28, 1899, were often subjected to considerable 

 dilution on account of the great amount of fine silt in the collections, 

 from Vio "to Yioo being the limits of dilution as a rule. 



The even distribution of the organisms in the Rafter cell was 

 secured by shaking the collection in a mixing cylinder gently till 

 the sediment was thoroughly distributed, and taking the sample 

 immediately with a long 1 cm. 3 pipette, inserted to the bottom of 

 the jar and raised to the surface during the filling process, and by 

 discharging the contents immediately into the cell at one corner, 

 the cover having been previously displaced at a slight obliquity to 

 admit the end of the pipette. With the filling of the cell the cover 

 automatically moves into place, and practice soon enables one to 

 fill the cell without inclusion of air bubbles. With the exception 

 of the heavier rhizopods, all of the organisms are as a rule very 

 evenly distributed by this method. 



The identification and enumeration of the contents of the cell 

 were carried on with the help of a mechanical stage and a f Bausch 

 & Lomb objective, with a Zeiss C for higher magnification when 

 needed for the detection of fine details or for counting the smaller 

 organisms in the filter-paper catches. 



After considerable experimenting, the following method was 

 established in the work of enumeration. Four sheets, each with 

 numbers 1 to 76 at the left, were fastened temporarily to accom- 



