519 



RELATIVE NUMBER OF SPECIES IN THE PLANKTON OF QUIVER CREEK AND SPOON 



AND ILLINOIS RIVERS. 



Group 



Algae — totals 



Schizophyceae 



Chlorophyceae 



BacillariaceEe 



Conjugal as 



Protozoa —totals 



Rhizopoda 



Heliozoa 



Mastigophora , 



Ciliata 



Suctoria 



Rotifera — totals , 



Rhizota 



Bdelloida 



Ploima 



Crustacea— totals 



Copepoda 



Cladocera , 



Ostracoda 



Other Crustacea 



Miscellaneous — totals . . , , 



Insect larvae 



Other forms 



Total No. Species 



Quiver 

 Creek 



60 



Spoon 

 River 



Illinois 

 River 



170 



429 



method and season of collection. The meager representation 

 of the Ciliata may be due to the absence of sewage contamina- 

 tion and hence of excessive bacterial development in the creek 

 waters. The food supply of many species is thus lacking. The 

 absence of a well-developed phytoplankton, aside from dia- 

 toms, and the fact that much of the vegetable debris of the 

 silt is only in the early stages of decay may account for the 

 small number of species of Rotifera and E}itoiiiostraca, groups 

 which in part depend upon these sources of food either directly 

 or indirectly. The recent origin of the creek water from rain, 

 or springs and ground seepage, affords insufficient time for the 

 breeding, not only of these organisms which form the more dis- 

 tant links in the chain of food relations, but also for many of 

 the nearer ones, such as the algse, which subsequently do ap- 



