16 
relations existing between the different groups. The plants are 
more abundant (and generally smaller) than the animals, outnum- 
bering them nearly 5 to 1. Computation shows that for each one of 
the Cladocera there are 7 Copepoda, the predominance of the latter 
CONSTITUENT GROUPS OF THE ANNUAL PLANKTON OF THE ILLINOIS RIVER. 
AVERAGE OF 52 WEEKLY COLLECTIONS IN 1898—-NUMBER PER M32. 













| ae et Number of 
eet individuals 
recorded. ae : 
en eS ae = = 
Alge: 
Bactenacecc aay ie ieee eee 3 (57,142 ,822)* 
lela ZO OMCeEoarucpatinwe docu Gos caogowecace 9 85,909,985 
Chiorophyceci meas. 1a sort oer ee ee eee 33 935,175, 105 
BIG THENSEED. ooo noc nose cébbosdconaod cans Bo 396,192,716 
Conjupatawass 44k gtictcn 0 SLRS ee ON Oe a 7 48,459 
IPhanero Satins Sect a. can <a See ce Eee| 2 9 
RetalfphytoplanktontSees se ee eee eal 535,326,274 
Brotozoa—totalls as). uk vars a he ee | ( 185) } ( 1 1 ile 734 , 000) 
MAStiCO phOrasaaa namie owe sleet aa oe 68 95,856,449 
hizo pOdarmte sees POSER eae. tov atrs cto 59 55,364 
lmabehtey Aone Legenienss BYR MRC eo rar oks Bere picks ia mots | Sen 4,871 
SPOLOZO dey ccisr lameness hao PAS cane a eR oe ee | 3 1,638 
Cilia ae ae ey ee ee | 45 15,812,346 
SUI CLOIIE sary NS see ae cae Ae eee | S| 332 
JERoh es hen cee a ean aS no RR ERE ATA Oe Wah UN eer 104 | 592,416 
Bimtomostraca=—tOvall mime ge sa micice anne eens one (43) (47 ,041) 
Cladoceray. . ay Sab ais wet Gan en eee | 26 6,242 
Ostracodaa.tern a Tet ne  eee | 4 191 
Copepoda es cn tates ee creo a ee 3) 40,608 
Miscellaneous sac. eae eee 114 9,393 
Motalezooplamlctomts seen ase eee 446 112,379,850 
Total planktonts enumerated............. 529 647 , 706, 124 
Synthetic (chlorophyll-bearing).................|. ett Ae Nears 017 986 ; 
Analytic (non-chlorophyll-bearing)............../.:......... 34,687,781 


being accounted for in part by the fact that their larval stages are 
free-s vimming and appear in the enumerations, while the young of 
the Cladocera are not set free until nearer maturity. About 10 to 
20 per cent. of the Copepoda are adults. The relative numbers of 

* Represents fragments of filaments, and is not included in totals. 
