ZZ 
Of the 18 pulses listed in the preceding table 17,fall within the 
limits of periods included in Plates I. and II. Of these 17 there are 
7 which coincide with, and 9 which follow shortly after, the culmina- 
tion of the pulses of the chlorophyll-bearing organisms, while 1, a 
small one in March, 1896, shows no such correlation. Food is thus 
a primary factor in the production of these recurrent pulses. As 
will be seen in Table I.,these pulses uniformly coincide with those 
of the total Ploima, and a similar relation may be followed in prior 
years. 
The eggs of this species are not usually carried by the female for 
any length of time, and are rarely found attached in preserved 
material. For this reason the sexual cycles are not easily followed 
with accuracy in the statistical data. It may be seen in Table I. that 
the free winter eggs belonging to both species of Svucheta are most 
numerous in the period of the larger pulses, and that their occur- 
rences show some tendency to coincide with these pulses. Proof 
that these pulses terminate in sexual reproduction is thus lacking, 
though it seems probable from some of the evidence. 
Syncheta pectinata has not been widely reported from American 
waters. Jennings (94) finds it in Michigan and Kellicott (’97) in 
Lake Erie, but it has not been elsewhere reported in American 
plankton. It appears, however, in many European records. Skori- 
kow (’96) finds it in the summer plankton of the River Udy, in 
Russia ; Zimmer ('99) finds it in common with S. tremula in the Oder 
throughout the year. He makes the statements-that it is never 
rare, 1s somewhat more abundant in the spring, and is, at other 
times, present “in relativ gleichmassiger Haufigkeit.’”’ In the 
light of our results it seems probable that the data at Zimmer’s 
disposal were insufficient to justify his conclusions as to the uniform- 
ity of its seasonal distribution. Schorler (’00) finds it in the Elbe 
in April, May, and October, with a maximum in May. Lauterborn 
(’98a) finds it perennial in the plankton of the Rhine, and lists it 
among the dicyclic species with two periods of sexual reproduction, 
one in April and one from the end of July to October. Judging from 
the character of the statistical data which have been presented for 
this and other species in the Illinois it seems probable that the later 
period noted by Lauterborn may include several cycles, and that 
the species is usually a polycyclic one. Seligo (’00) reports it 
perennial in waters near Danzig, with largest numbers in April and 

