509 
tion again drops toa low level, and this movement appears in 
60-70 per cent. of the instances in each month. In December 
the decline in production is checked, and in a few cases the 
upward tendency reappears, only to give way again in most 
cases to the January minimum. 
There is thus a general seasonal regimen apparent in the 
totals of all localities, and an approximately parallel seasonal 
routine for each of the localities, the degree of approximation 
varying with the locality and the season. But this regimen can 
be outlined only inthe most general terms, and is everywhere 
subject to divergences that frequently reduce it well nigh toa 
semblance of chaos—a condition arising from the instability of 
this aquatic environment. 
The course of production above outlined considers only the 
movement of the average monthly production, and consequently 
deals only with the larger and more general seasonal move- 
ments. It masks almost completely the minor fluctuations, 
and especially obliterates all consideration of the phenomenon 
of pulses discussed in the treatment of the course of produc- 
tion in the several localities. 
It is inthis matter of pulses, or,in other words, in the cyclic 
movement in plankton production, thatthe nearest approach to 
a normal regimen appears in our volumetric data. I have 
shown that wherever our collections were made at intervals of 
a week, or less, this movement is generally distinctly traceable. 
In the backwaters, where collections were usually less frequent, 
the cyclic character of planktographs is still apparent, even in 
fortnightly collections. This phenomenon is therefore, it seems, 
a constant feature of the movement in plankton production in 
our waters as it appears in the purely volumetric data. Sug- 
gestions of the occurrence of a similar movement in the plank- 
ton of other waters may be found occasionally in the data of 
other investigators, but nowhere, to my knowledge, is there at 
present a chronological series of collections of sufficient dura- 
tion and brief enough interval of collection for comparison 
with the data presented in this paper. The main basis for the 
