PLANKTON OF LAKES WAUBESA AND KEGONSA 129 



baena, Aphanizomenon, Lyngbya, and Microcystis, while the most im- 

 portant diatoms were Melosira, Fragilaria, and Stephanodiscus. 



The largest quantity of organic matter noted in the net plankton of 

 1915 was found in the catch taken on October 2 (No. 5153). In this 

 maximum catch, only two Crustacea appeared in considerable numbers, 

 namely, 17,100 Cyclops per cubic meter of water and 44,000 Chydorus 

 per cubic meter. The rotifer Anuraea cochlearis averaged 26,200 indi- 

 viduals per cubic meter, while Ceratium numbered 905,000. There 

 were 614,000 colonies of Microcystis per cubic meter of water in this 

 catch and slightly more than a million masses of Anabaena per cubic 

 meter. The most abundant forms at this time, however, were the 

 diatoms Melosira and Stephanodiscus, the numbers being, respectively, 

 4,123,000 and 4,500,000 per cubic meter. 



In 1916 the Crustacea showed a June maximum and an October maxi- 

 mum, with a more or less pronounced minimum during the intervening 

 months. Diaptomus, for example, numbered 3,500 individuals per cubic 

 meter of water on June 15 and 4,200 on October 2, with a minimum of 

 800 on August 8. Cyclops gave a maximum of 8,000 per' cubic meter on 

 June 29 and another of 13,100 on October 2, with a minimum of 1,500 

 on July 25. The copepod nauplii ranged from a minimum of 4,300 per 

 cubic meter of water on July 25 to a maximum of 19,500 on October 

 30; a secondary maximum of 18,500 was noted on July 11. Daphnia 

 pulex was most abundant on June 29, namely, 3,000 per cubic meter 

 and its numbers were negligible in the catches taken after July 11. 

 DapMia hyalina yielded a maximum of 13,700 individuals per cubic 

 meter on June 29 and one of 11,200 on October 2, with an intervening 

 minimum of 900 on August 8. Chydorus, on the other hand, showed 

 no distinct maximum during the early part of the season, but the num- 

 ber rose to 40,500 individuals per cubic meter on September 19 and 

 again to 52,000 on October 30. 



Anuraea cochlearis was the only rotifer found in considerable num- 

 bers; 223,200 individuals per cubic meter were obtained in the catch 

 secured on October 2, 1916. Ceratium attained a maximum of 2,200,000 

 per cubic meter on August 23 and it stood a little above two million on 

 October 2. 



Microcystis was found in greatest abundance on September 19 when 

 2,734,000 colonies per cubic meter of water were obtained. The number 

 of masses of Anabaena rose slightly above one million per cubic meter 

 on September 7, while Lyngbya was rather scarce during the entire 

 season, the largest number being 490,000 filaments per cubic meter on 

 July 25. The diatom Melosira rose to a maximum of 3,286,000 filaments 

 per cubic meter on October 18, while Stephanodiscus reached a maxi- 

 mum of 2,914,000 individuals per cubic meter on the same date. 



