METHODS. 
The collections were preserved in bottles of uniform capacity 
(60 cm.%), 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.* of a suitably diluted plankton is 
distributed evenly ina cell 20x50 mm. The plankton was diluted 
or condensed (from 60 cm.* 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 
lareer collections in 7/,, to */,, of the total catch; and the smaller 
organisms in +/,, to ‘/s. 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, 
inom /, tO ~/,,, 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.’ 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 3? 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- 
