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 M3. 
eS 2 Number of 
acre deine individuals. 
Alge: 
Ba Cteniaice coins Wachee ee ees 3 (57,142 ,822)* 
SCM ZOPANClGs. wissen: ode ee ein tea oR 9 85,909 ,985 
Chioropliyeceidianee tree etic: eee 33 535175005 
Bacillatiaces2s 40m ce easoe ae ke Leen epee 29 396,192,716 
Competes nts Seren nas ak. BS ea eee ee 7 48,459 
Phaneto canmia aesag sm stas is gels ee ee 2 9 
Totaly phytoplamietombss 0.21... sent pire ecu | 83 539 5.320%, 20 
Preto zo —LOtalk, magith «ics SA nh eee eee | (185) | (111,734,000) 
Masticophoranycie tenses seein soca enact ell 68 95,856,449 
Rib Zopocla tance tone steerer ier cie mes 59 55,364 
IGIIGZO dite eee Aa ee eR ae hte te ee eal ee 5 4,871 
SPOLOZOAT oe sek Riese Ce Be Co eras | 3 1,638 
Ciliata ete eines ww etaee es Oe TE apne 45 15,812,346 
SUCTOTIat ce MORE ae CREE ice) cake ornee os 5 SO 
ARO ILET Uae erro Oe oe hate ok ae On Ee 104 592 ,416 
DimOimOg nei — HOW 55 coon apo one vloneoocaous (43) (47 ,041) 
GIAO Cera eee ccs tess ees ae ME rt een ae 26 6,242 
Ostracoda srr esies se sat ee eee aA es 4 191 
Copepodain ier lad So usenet eNMeIpp eeaee eee 13 40,608 
MiScelilanme ous serpent teak valence eee 5 ears 9 Ui rea cree 114 9,393 
MotalizooplanikctontS see eee eee 446 112.379 850 
Total planktontsenumerateds).- 4.6.46 se 529 647,706,124 
Synthetic (chlorophyll-bearino)i e000 hare bret a || eee 613,017,986 
NGakbypene ((caronai-elalloncoyolmvalll-levernaun)), 05850005 n500lbo000005040 34,687,781 
being accounted for in part by the fact that their larval stages are 
free-swimming 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. 
