509 



tion again drops to a 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 in the most general terms, and is everywhere 

 subject to divergences that frequently reduce it well nigh to a 

 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 in this matter of pulses, or, in other words, in the cyclic 

 movement in plankton production, that the 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 



