_ Drxon & Joty—On Some Minute Organisms. 743 
portion. This was treated in a centrifugal apparatus. By this 
means the water was cleared of all turbidity, and its solid contents 
were thrown to the bottom of the test tubes of the centrifuge, in 
the. form of a compact mat of whitish gray material. 
Examination of this material showed at once that coccoliths 
abounded in the free state in the sea-water. Their numbers, 
indeed, exceeded all anticipation, for there were about 100 on 
each slide prepared from the precipitates which formed in the 
centrifuge. An estimate of the actual number present in the sea 
is equally astonishing. A sample of water taken 3 miles off the 
coast, on a calm day, afforded 200 coccoliths in each cubic 
centimetre. The estimate was made by permitting the solid matter 
of a large volume of water to settle. The clear upper fluid was 
then siphoned off, and the remainder with the solid contents of 
the whole was vigorously shaken up. The number of coccoliths in 
a drop of this latter was then estimated by means of a divided 
stage (such as is used in counting blood-corpuscles). From 
this the number present in the original volume is obtained. 
Several closely agreeing estimates of the number present in the 
same sample gave the above-mentioned remarkable result. 
The centrifuge was an efficient way of getting large numbers 
of coccoliths, but all the solid matter suspended in the water was 
so closely compacted by its action that a clear view of the contained 
organisms was often difficult to obtain from this material. Later 
on, we found that the simplest manner of obtaining these bodies 
was straining large quantities of sea-water through fine silk; a 
procedure which, in the anticipation of finding but very few 
specimens, we did not at first adopt. The silk should be stretched 
as a diaphragm across the lower end of a wide glass tube (the 
chimney of an argand-burner answers well for this purpose), and 
while the latter is held in a vertical position, sea-water is poured 
in above. After many gallons have passed through, the silk is 
removed, and washed in a small quantity of water, and the 
washed-off precipitate bottled. We found this method more 
satisfactory than towing the strainer in the water. In the latter 
ease a backwash, which may lead to the loss of much of the material 
gathered, is always liable to occur. 
These methods supplied us amply with material to study 
the form and manner of occurrence of the coccoliths. These 
SCIEN. PROC. R.D.S., VOL. Vill., PART VI. 3 if 
