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 cubic 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 it is just 50 percent., in 111 cases it is below this, 

 and in 111 above. 



TABLE SHOWING DI-.TK1 BUTTON ACCORDING TO PERCENTAGE OF DECREASE OF 

 243 CATCHES MEASURED BY GRAVITY ANO 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 



1 



62 



4 



52 



4 



42 



3 



32 



3 



75 



1 



61 



5 



5i 



5 



4i 



2 



3i 



1 



74 



2 



60 



5 



50 



21 



40 



4 



29 



5 



7i 



1 



59 



9 



49 



8 



39 



1 



27 





6o 



1 



58 



9 



48 



1 1 



38 



7 



26 





67 



4 



57 



10 



47 



10 



37 



5 



25 





66 



4 



56 



5 



46 



7 



36 



4 



22 





65 



3 



55 



12 



45 



9 



35 



4 



21 





64 



5 



54 



7 



44 



6 



34 



4 



13 





63 



3 



53 



11 



43 



9 



33 



■1 



8 





