94 
by current, waves, seines, boats, and fish make relatively larger 
contributions at low-water stages to the diversification of the 
plankton. In addition to these factors, however, there is abun- 
dant indication that many individuals assume during the warmer 
months a eulimnetic habit, and that some of the Rhizopoda 
become, for the time being at least, typical, though temporary, 
planktonts. 
It naturally follows that in so far as the plankton is concerned, 
the Rhizopoda exhibit a seasonal preference for the warmer months 
above 60°. Maximum numbers were attained only at the higher 
temperatures save in those instances where they attend winter 
floods. Ina measure the seasonal distribution of the Rhizopoda in 
the plankton reflects that of the group in its normal habitat; but at 
the best the picture is incomplete. 
The Rhizopoda have important relations in the economy of the 
plankton. They feed upon diatoms, desmids, the smaller alge, and 
even the chlorophyll-bearing Mastigophora such as Trachelomonas 
and Carteria. Their occurrences in the plankton do not exhibit any 
striking correlation with those of the groups named. The great 
pulse of September 7, 1897, for example (Pl. II.), lies in a depression 
of the diatoms and coincides with pulses of Chlorophycee and 
Mastigophora, and that of August 10 (68,400) exhibits a similar 
relation, the diatoms rising the following week as the Riizopoda 
fall. In 1898 the pulse of Riizopoda on June 28 of 37,000 (Table I.) 
culminates a fortnight after that of the diatoms and Chlorophycee 
and a week after that of the Mastigophora. It thus 1s intercalated 
between the June and July pulses of these chlorophyll-bearing 
organisms (PI. II.). The Rhizopoda pulse of July 19 (28,800), on 
the other hand, occurs with the coincident pulses of the three 
groups named (Pl. IJ.). The immediate diluent effect of flood 
waters upon the plankton combined with their tendency to increase 
the number of adventitious Rhizopoda results at times in the 
intercalation of their pulses with those of the chlorophyll-bearing 
organisms whose relative numbers are reduced by the dilution. The 
data evidently do not afford any adequate solution of the inter- 
calations of the Riizopoda with other organisms. 
The Rhizopoda are very frequently found in the digestive tract 
of limnetic rotifers, but I have never noted the Entomostraca feed- 
ing upon them. They are important elements in the food of young 
a ee 
