214 
PuLSES OF SYNCHETA STYLATA—continued. 
































| | | | 
Year | Date Temp. | No. | Date Temp. | No. Date Temp. No. 
| | | | | 
| 
1894 | -—— 
1895 | | | Aug. 1 79° | 10,287 | Sept.27 | 73° (20208 
1896 es ——— || Ane, 8 86° 8,400 | 
° | | 
1897 July 21 So e103 200 | Sept. 7 80° 28,000 
1898 July 19 34° 64,800 | Aug. 2 79° | 170,400 | Sept. 27 73° 265,600 
TT Oe Bae 24,800 
Year Date | Temp. No. | Date Temp. No. Date | Temp. No. 
| | | | 
| | | 
1 894 Octy e179) 58° 9 263;.9351)] | — — 
| | | | | | 
1895 | | | Nov. 27 33° | 901,901 | Dec. 11 32° | 1,121,056 
| | | | | 
1896 | | Nov. 17 44°} 114,000 | 
1897 | Oct. 5 | 71°] 12,000] Nov. 9 50° 26,400 | Dec. 14 36° 72,200 
| fe 498) y 652)! ) ase s00 “30° | 34.59 87,200 
1898 Oct. 25 49° | 824,500] Nov. 15 41° | 110,000 | Dec: 6 34° 42,500 
S220 33° 59,200 






This is the most abundant of all the rotifers in our plankton, 
exceeding by 30 per cent. Polyarthra, the next in abundance. It 
constituted one fifth of the total Plowma in 1898, and is accordingly 
a large factor quantitatively and ecologically in the economy of the 
plankton of the Illinois River. 
It is a perennial planktont, occurring in six sevenths of our 
collections and usually in considerable numbers. The distribution 
in 1898 (Table I.) is a fair index of the usual seasonal routine, with 
the exception that in all prior years the July-August minimum is 
more pronounced and better sustained. The development in 
January—February is never large, rarely exceeding 20,000. In 
March, numbers rise rapidly, usually with a minor pulse, the re- 
covery from which in April culminates in a vernal pulse, which in 
three of the six years was the largest of the year. Following this 
vernal pulse there is a series of smaller pulses throughout the sum- 
mer. The decline of the June flood, when this occurs, seems to offer 
favorable conditions (cf. foregoing table and Pt. IJ., Pl. [X.—XII.) 
for the development of a pulse which is but little smaller than the 
vernal one. It may be of some significance that this pulse and the 
to 
