120 University of California Publications in Zoology [Vol.22 



The Rotifera (pi. 19) show substantial agreement with the Ciliata, 

 both collectively and individually. Hence we are still further led to 

 doubt the dominance of temperature. 



As to Entomostraca (pi. 19) the catches of Cladocera were too 

 variable to give any information, and those of Copepoda were also 

 rather indefinite. There was not much difference between the forenoon 

 and afternoon catches either of Cladocera or of Copepoda or of both 

 together. 



As shown by plate 1, the whole plankton volume increased strongly 

 through most of the twelve hours, both actually and also relatively 

 to the volume of sediment. No explanation of this fact seems to be 

 available, although the distribution of the chlorophyll bearers may 

 be of sufficient importance. 



The foregoing discussion leaves a final impression which is badly 

 muddled. This may truly represent the facts, but it is not satisfying 

 to the mind. A different form of discussion may help to clear the 

 problems involved. Examination of tables and plates already men- 

 tioned discloses the fact that, based on distribution through the twelve 

 hours, there were two fairly well marked groups of planktonts, con- 

 sisting on the one hand of the chlorophyll bearers and on the other 

 hand of the more highly motile animal forms. The former showed 

 a steady increase in numbers as the hours of afternoon passed. The 

 latter showed just as pronounced a decrease, though less uniform, 

 from the forenoon numbers. 



Apparently the general factors which could probably be involved 

 are the following: vital, chemical and physical. While specific sub- 

 divisions of these make a formidable list, which is further complicated 

 by their very general interdependence, it seems that some are suffi- 

 ciently dominant to enable tentative discussion, as in the accompany- 

 ing list : 



Vital Factors Chemical Factors Physical Factors 



Locomotion Organic content Viscosity 



Irritability Mineral content Turbidity 



Feeding Gaseous content Suspended solids 



Respiration Currents j™?. 



Excretion (Wind 



Reproduction Oscillations 



Other organisms Temperature 



Light 

 Pressure 



Locomotion, among the vital factors, is characteristic of the typical 

 animal forms, but its effectiveness may be increased or diminished by 

 respiration and excretion, or other factors, in the same animal or in 



