474 



The Ohio Journal of Science [Vol. XIX, No. 8, 



The distribution of Ceratium throughout the series is most 

 interesting. This protozoan was present in successively and 

 sharply decreasing numbers with increase in the age of the 

 pond. There were enormous numbers of it in the one year 

 pond. In the five year pond there were only one-fourth as 

 many and in the ten year pond there was a sharp decline from 

 this reduced number to scarcely one-fifth of it. This one-fifth 

 was reduced by fifty per cent in the fifteen year pond. In the 

 thirty year pond there was only a trace of Ceratium. Appar- 

 ently, then, Ceratium found its optimum conditions in the two 

 younger bodies of water. That this condition is a matter of age 

 rather than of distribution or location merely, is borne out by 



TABLE 25. 

 SltmmaRy of Qvantitative Plankton Results per 100 Liters. 



Species 



Ceratium longicorne 



Rotifera 



Arcella vulgaris 



Nauplius 



Dinobryon 



Cyclops 



Chydorus 



Daphnia 



Blue-Green algae 



Pediastrum 



Pleodorina 



Cy pris inequivalva 



Cy pris sp 



Closterium 



Potamocypris 



Cyclops ater 



Bosmina longirostris 



Scapholebris 



Ophryoxus 



Ceriodaphnia 



Total number of individuals 



Ponds 



1 Year 



850,000 



4,500 



4.000 



15,625 



1,325,000 



2,000 



1,500 



2.199,125 



5 Year 



203.125 

 2,231 

 6,250 

 7,500 



6,696 

 2,000 



1,000 

 750 



225,802 



10 Year 



11.160 

 10,892 

 Few 

 55.800 



685.250 

 17,850 

 67,000 



847,952 



15 Year 



5,250 

 5,750 

 5,375 

 Few 



5.890 



6.250 



535,750 



5,000 



569,265 



30 Year 



Trace 

 2,000 



Few 

 2,250 



1,000 



6.300 

 1,250 

 2,250 

 2,250 



15,300 



the fact that the oije, ten and thirty year ponds are within half 

 a mile of each other, whereas the one and five year ponds are 

 five miles apart and in somewhat different surroundings. 

 Furthermore, towings taken at various intervals during the 

 summer for three years, showed that the differences were not 

 merely a matter of pulse. 



In general, then, it can be said, regarding the zooplankton, 

 that the percentage of entomostraca increases with age and in 

 the older ponds, forms the greater part of the plankton animals, 

 although the data do not show an absolute increase in numbers. 

 On the other hand, the protozoa and rotifera form the greater 

 part of the zooplankton in the two younger ponds. 



