294 
the data where collections are of sufficient frequency to adequately 
delineate the curve of production, that 1s from July, 1895, to Oc- 
tober, 1896, and from July, 1897, to March, 1899, a total of 37 
months, and suggestions of a like phenomenon appear in the less 
complete data of other years. The degree of agreement indicated 
in the pulse of July, 1898, will be found,on examination of the data 
in Table I. and in the plates of this paper, to vary with the environ- 
mental conditions. Times of rapid change in hydrographic condi- 
tions or in temperature generally show less agreement, and more 
stable conditions will exhibit an equal or even greater uniformity 
in the prevalence of the pulse-like rise and decline of the component 
organisms. 
In order to show the course of these recurrent pulses in the 
chlorophyll-bearing planktonts, the total Chlorophycee, Bacal- 
lariacee, and chlorophyll-bearing Mastigophora on the one hand, and 
of the Rotifera and Entomostraca (‘‘Crustacea”’ of the plates), I have 
presented the data graphically on Plates I—IV., and in the table on 
pages 296-299 have drawn up a list of the pulses, indicating the 
dates of the collections which in the main enter into the respective 
pulses, and the dates of the maxima or culminations of the five 
groups named. Owing to the irregularities in the data, there are 
some instances in which several possible dates might have been 
chosen. Reasons for the choice are in several important instances 
given in the foot-notes to the table. 
It is evident from the data here presented in graphic and tabular 
form that the pulses of the five groups of organisms tend in the main 
to coincide. This is shown in Plates I.-IV., and in the fact that the 
average divergence of 175 group pulses listed in the table is 6.4 
days, or, if 5 aberrant instances are omitted, only 4.8 days. In other 
words, the pulses of the totals of the 5 groups included in the table 
culminate on an average within an interval of 6.4 (4.8 in 170 cases) 
days. The average of the extreme limits between maxima of 
eroup pulses in the 36 periods of movement listed in the table is 
11.7 days. 
It is apparent that the pulses would be more completely de- 
lineated by collections at daily intervals, but even in the somewhat 
irregular and at times chaotic data here presented, the evidence 
seems conclusive that the seasonal production of the dominant 
species and groups of planktonts tends to fall into coincident 
