206 
This was not true in other years, but collections in those years were 
too infrequent to trace the seasonal distribution of the species with 
accuracy at that season. It is volumetrically of some importance 
in determining the quantitative fluctuations in the total plankton. 
Computations based on its average size indicate that approximately 
600,000, including eggs, would be required to form 1 cm. of plank- 
ton. On this basis, and allowing 10 per cent. for interstices, it 
constituted at the time of its vernal maximum in 1898 about 10 
per cent. of the total volume of the plankton (silk-net catch). 
The table on pages 204 and 205 lists 43 pulses, of which 6 le out- 
side of the period included in Plates I.and II. Of the 38 remaining 
pulses 16 coincide in location with the whole or a part (in case of 
divided culminations) of the pulses of the chlorophyll-bearing organ- 
isms; 12 follow at the next collection, usually at intervals of one 
week; and 6, after a fortnight. The remaining 4 do not bear this rela- 
tion, occurring in autumn or midwinter, when all pulses were feeble 
and ill-defined. A comparison of Plates I. and II. with V. will 
show that not all of the chlorophyll-bearing pulses are attended by 
pulses of Polyarthra; nor is there any constant relation, excepting 
the vernal pulse, between the size of the pulses of the two groups 
of planktonts in question. Nevertheless, the dependence of the 
recurrent periods of rapid multiplication of Polyarthra upon the 
rhythmic occurrences of the chlorophyll-bearing organisms upon 
which they largely depend for their food is strongly suggested by 
the data here offered. Food relations thus dominate the repro- 
ductive cycles. 
The pulses of Polyarthra form a considerable portion of many of 
the pulses of the total Plowma, and it is but natural that we should 
find a coincidence in their locations. This may be followed for 1898 
in Table I. Ina number of instances the culminations of the pulses 
are not exactly coincident, but separated by the interval between 
two collections. The association of the two pulses is, however, 
apparent in every case, and a similar relation may be traced in prior 
years. 
These recurrent pulses afford evidence for the polycyclic habit 
of this species. Additional proof of this phenomenon is found in the 
evidences of sexual .reproduction—either male or winter eggs 
attached to the female—which have attended many of the pulses. 
The eggs of this species, both summer and winter forms, are very 
