742 THE AMERICAN NATURALIST. [VoL XXXII. 
of the precipitate. The space required, the tediousness, the 
loss of organisms, the fact that in this new process very many 
forms break up before all the material is settled have led to its 
abandonment in favor of the employment of centrifugal force. 
Previous to 1896 Cori devised a simple hand centrifuge and 
used it for collecting infusoria for class work. Last year 
a brief reference was made to our work with the centrifugal 
The Planktonokrit. 
method (Field, '97, I). Since then Kofoid ('97) has experi- 
mented on similar lines. His machine is “geared to give 
3000 to 4000 revolutions per minute and arranged to act 
upon a continuous stream of water, all of which was subjected 
to the maximum and uniform action of the centrifugal force.” 
This machine secured in some instances 98% of the planktonts. 
But as I pointed out last year, it is not so efficient with those 
organisms whose specific gravity is about that of water, such 
as the Cyanophycez, Anabcena, Clathrocystis, eż al. 
Experiments have been made with the centrifugal machine 
devised by Dr. C. S. Dolley, called the Planktonokrit, and 
