14 VICTOR | . -Ill LI-UKD. 



The table shows that the number of bacteria is greater in tin- 

 older ponds, except in 5* which is noncomparable because of 

 contamination. 



(4) The Plankton. The study of the plankton has been prac- 

 tically limited to the Entomostraca the most important food 

 of young fishes. The presence of a larger number of rotifers 

 and protozoa, etc., is observable as we pass from the younger 

 to the older ponds. 



The number of Entomostraca in approximately 90 liters of 

 surface water, to a depth of 10-12 decimeters, is given in the 

 table below. It was thought best to simply clip the desired 

 amount from the water while walking and strain the dippings 

 through a bolting cloth strainer. After the first collection this 

 was repeated in as uniform a manner as possible and Birge net 

 collections were made at the same time for comparison. There 

 was no great discrepancy in the results of the two methods of 

 collecting, except in the case of Ostracoda in pond i4/>. As com- 

 pared with dippings, some Birge net collections showed less 

 Ostracoda. Ostracoda w r ere probably started from the bottom 

 by the feet of the collector but were not by the drawing of the 



Birge net. 



TABLE XYIII. 



THE NUMBER OF ENTOMOSTRACA IN 90 LITERS OF WATER. 



The table shows that with the exception of pond 5^, which 

 is probably noncomparable because of contamination, the older 

 ponds contain most Entomostraca except in early spring when 

 conditions are somewhat reversed. 



A large quantity of plankton in old ponds has been noted lor 

 sevcral years in connection with class work. For comparison 

 with the; ponds under consideration we have studied \Yoll Lake, 



