255 
at the rate of 1,000 revolutions per minute, resulting in an appli- 
cation of 1,420,484 dynes. All records and discussions in this 
paper are based upon this method of measurement. It brings 
about a considerable reduction in the volume of plankton as 
compared with that recorded by the usual method of allowing 
the plankton to settle in the Eggert color-tubes for twenty-four 
or forty-eight hours and condense by gravity only. I have de- 
termined the amount of this reduction in measurement of all 
planktons collected by us up to June 6, 1896. There are two 
hundred and forty-three of these catches, and they represent 
the full seasonal and local range in quantity and quality, cov- 
ering, as they do, a period of two years and all the localities 
with which we have dealt. The actual quantity of plankton 
handled in these tests ranges from .025 to 10.25 eubic centi- 
meters (centrifuge measurement), and 143 of the 243 catches 
lie between .25 and 2. cubic centimeters. 
The average decrease in volume when determined by the 
centrifuge as compared with that by the gravity method in 
these 243 cases was 49.5 per cent. As shown in the following 
table, the decrease ranges from 8 per cent. to 76 per cent. In 
21 cases itis just 50 per cent., in ill cases it is below this, 
and in 111 above. 
TABLE SHOWING DISTRIBUTION ACCORDING TO PERCENTAGE OF DECREASE OF 
243 CATCHES MEASURED BY GRAVITY AND CENTRIFUGE METHODS. 
Per No. Per No. Per No. Per | No. Per No. 
cent. of cent. of cent. | of cent:*|) of cent. of 
lost | catches lost catches} lost | catches} lost ;catches} lost | catches 
76 I 62 4 52 4 2 | 3 32 3 
75 I 6u | 28 51 5 41 | 2 31 I 
74 2 60 | 5 50 21 40 4 2 5 
71 I 59 9 49 8 39 I 2 I 
69 I 58 9 48 II 38 7 26 I 
67 4 Sie eLO) 47 10 37 5 25 I 
66 4 56 | 5 46 7 36 4 22 I 
65 3 55 12 45 9 35 4 21 I 
64 5 54 | 7 44 6 34 4 13 1 
63 3 53 II 43 9 33 I 8 I 
