295 
recurrent pulses, which, in turn, are the cause of the similar and 
often coincident volumetric fluctuations. 
Attention should be directed to the fact that without any im- 
portant exceptions this recurrent movement pervades all the 
organisms of the plankton which are eulimnetic,—such as Scenedes- 
mus, Melostra, Trachelomonas, Codonella, Syncheta, Daphnia, and 
Cyclops,—and often those which at certain seasons become tempo- 
rary planktonts, such as Dafflugia and Hydra, but not with any 
regularity the tycholimnetic organisms, such as bdelloid rotifers or 
nematodes. It affects the more highly organized Rotifera and 
Entomostraca with slower growth, longer life, and consequent 
greater cumulative function as well as the alga, diatoms, and 
flagellates, where rapid multiplication, brief existence, and non- 
cumulative (in the individual) function prevail. The large share 
which the young (eggs and immature stages) play in the pulses of 
Rotijera and Entomostraca will be seen in Table IJ., and repeated 
attention has been called to this in the discussion of species. The 
prevalence of breeding females and of eggs or young during the rise 
of the pulse, and of eggless, moribund, or dead individuals or their 
skeletons during the decline, is a common phenomenon in all well- 
defined pulses. No species of plankton organisms appears to escape 
the operation of this recurrent movement in production. 
The proportion of individuals surviving from one pulse to the 
next is subject to great variation, being often least when the ampli- 
tude of the pulses is greatest,and largest when the pulses culminate 
at slight amplitudes. As a result of periods of minimum develop- 
ment, it follows that the possible length of life of most plankton 
organisms, even of the Rotifera and Entomostraca, in the plankton 
must fall within rather narrow limits of a few days or a fortnight 
at the most. Since the contrasts between minimum and maximum 
numbers are relatively greater among the chlorophyll-bearing 
organisms, it follows that the survival proportion is less in these 
groups. 
The duration and amplitude of the plankton pulses will vary 
within certain limits according to the method of delineation. The 
volumetric minima and maxima present the total product in cubic 
centimeters, and the pulses thus marked cat have been described 
in Part I. They may also be delineated by statistical data of the 
total plankton or of its larger groups of organisms, or by the domi- 
