161 
ASPLANCHNA PRIODONTA. 
Females Females Females Total 
Date Males | without | with sum- | with winter | .. ,.°° 
individuals 
eggs mer eggs eggs 
MiaelOR okies ce nee sok —— 3,200 —— — 3,200 
il Kee kong eRe: Ee sae 800 10,400 3,200 — 14,400 
OEE Te DAE A Soe nN Oe 120 1,600 200 200 BNO 
Peis cee es eae lh amas — 1,600 400 —_—— 2,000 
years, leads us to infer that the species may be polycyclic in our 
waters. 
This limnetic rotifer figures largely in the fresh-water plankton 
of other localities, attaining a relative development greatly surpass- 
ing that thus far found in the Illinois River. Apstein (’96) reports 
it of irregular occurrence in the smaller lakes of Holstein, and Seligo 
(00) finds it perennial in Prussian lakes, with maxima in April and 
September. Wesenberg-Lund (’00) also finds it perennial in Danish 
waters, with sexual cycles in May and September. Marsson (’00), in 
waters about Berlin finds a great variation in theseasonaloccurrence, 
but the intervals of his collection—four to six weeks—were too great 
_to follow seasonal distribution satisfactorily. Zacharias (’98b) finds 
it in the summer and autumn plankton in a number of German 
lakes and streams. Zimmer (’99) traces its appearance in the Oder 
from February to a maximum in May, from which time until the end 
of July it is “einer der haufigsten Planktonorganismen”’ (!). It 
then declines, but returns in small numbers in November. Schorler 
(00) records it in the Elbe from April to October, with maxima in 
April-June and September. Burckhardt (’00a) finds, on the other 
hand, that in Swiss waters it reaches its greatest development from 
December to March with a maximum in January-February. There 
are also secondary maxima in May—June and in August. Lauter- 
born (’93) finds it to be a dicyclic perennial planktont in the Rhine, 
with maxima in April and September—October. A part of the great 
variation in the seasonal distribution of this species which is ap- 
parent in this survey of the literature may be due to insufficient 
collections or too great an interval between collections. The species 
