134 MARIE V. LEBOUR. 
Winchester for Peridiniales and Protozoa, which perhaps include the 
most delicate of all the plankton organisms. The samples were all 
examined fresh when possible ; if impossible, which was only seldom, 
they were preserved by adding strong Flemming’s solution at the time 
of capture as advised by Gran (i912a). For most species this method 
of preservation was found very satisfactory. 
For quantitative estimation a certain amount (usually 50 cc.) of the 
sample water was put in tubes and centrifuged. Five tubes each holding 
10 cc. were examined, the tubes pointed at the end after Lohmann’s 
pattern, so that the contents may be emptied out and leave the residue in 
the point ; this residue was removed carefully with a fine pipette, put 
on a ruled glass slide and the contents counted. The water was then re- 
centrifuged and the process gone through again. It was found that 
although re-centrifuging answered very well for diatoms, Peridinium 
and the more sturdy organisms, it was no use for the fragile forms such 
as the naked Peridiniales and small Infusoria, many of which are most 
probably destroyed even before they are brought in. 
It was found by experiment that centrifuging for ten minutes gave 
the best results, the largest number of gymnodinians being secured in 
this way. This is longer than the time taken by Lohmann, but his 
centrifuge made many more revolutions than ours, the number of ours 
not being exactly estimated. 
The tow nettings were not exhaustively examined, but the most 
important organisms were noted and their relative abundance. The 
nets used were of silk with meshes 26, 50 and 150 to the inch respectively, 
mouth 56 inches in circumference (inside), and bottom 15 inches in cir- 
cumference. Length of silk clear of the calico to which it is attached 
at the ends, 39 inches. Area of silk, 1382 inches. Duration of haul, 10 to 
15 minutes, or in exceptional cases a few minutes longer. 
The following quick method was adopted: anything large first noted 
with the naked eye, then a certain amount of each sample taken, and when 
30 or more of any organism was present it was marked ec; if 20 but 
under 30, c; if 6 but under 20, 4-; if more than one but under 6, r; if 
only a single specimenrr. In this way a rough estimate of what is common 
in the tow nets is made. In the case of the very fine samples after stirring 
two separate drops with a pipette are examined and the above method 
applied. 
On the few days when it was impossible to go beyond the Breakwater 
the samples and tow nettings were taken from the west channel at the 
side of the Breakwater. For a fortnight in April it was impossible 
owing to the storms to go out at all. After this, about the 25th, the 
increase in plankton is large. The samples were as nearly as possible 
