ARTICLE X. STUDIES ON THE BIOLOGY OF THE UPPER ILLI- 

 NOIS RIVER. BY STEPHEN A. FORBES AND R. E. RICHARD- page 

 SON (21 Plates) June, 1913 481-574 



Acknowledgments 482 



Objects of the investigation 482 



Character and chronology of field operations 484 



Importance of the plankton 487 



Changes in river levels 487 



The river plankton 488 



The lake plankton 491 



River and lakes compared 493 



Causes of an increased plankton 494 



Illinois River work of 191 1 and 1912 495 



The microplankton, summer of iQii 496 



Definition of terms. . . 498 



The Sanitary Canal at Lockport 501 



Des Plaines River, Lockport 502 



Des Plaines River at Dresden Heights 504 



The Kankakee River at Dresden Heights 506 



Illinois River at Morris 507 



Imperfect mixture of waters 508 



Extreme midsummer conditions 509 



The bottom sludges 510 



Sludge worms 512 



Composition of the sludges 512 



Marginal conditions, July, 191 1 513 



Plants and animals of the stream in general, July, 1911 513 



Late summer and autumn conditions, 191 1 514 



Reappearance of fishes and other animals 514 



Winter conditions, 1912 515 



The winter search for fishes 515 



Summer and fall of 1912 516 



Illinois River at the Marseilles dam 518 



Above the dam 518 



Below the dam 522 



Ottawa 524 



Starved Rock 527 



La Salle-Peru 529 



Spring Valley 530 



Depue 531 



Hennepin to Henry 532 



Henry to Chillicothe 534 



Summary by stations 539 



The Sanitary Canal at Lockport 539 



The Des Plaines River at Lockport 539 



The Des Plaines River at Dresden Heights 540 



The Kankakee at its mouth 540 



Morris to Marseilles 541 



The Marseilles dam 542 



Ottawa and Starved Rock 542 



Spring Valley 543 



Hennepin to Henry 544 



Henry to Chillicothe 544 



General summary of chemical features 545 



July and August, 191 1 545 



September and November, 191 1 546 



