ANNUAL DISTRIBUTION OF THE ORGANISMS. 33 



in Green lake would be peculiarly favorable for Daphnia puLir 

 carlo,, but I have never found it, although my collections have 

 now covered a considerable number of years. 



In the other lakes examined in this investigation I found 

 Daphnia pulicaria only in Shamrock and Pansy of the Clover 

 Leaf lakes and in Pelican lake in two years. In the Clover 

 Leaf lakes it occurred below the thermocline. Its occurrence 

 in Pelican lake was somewhat unexpected, as this lake has no 

 thermocline, and the species was found in August, after the 

 lake was thoroughly warmed up. 



In former collecting trips I have found Daphnia pulicaria in 

 the deep waters of Lake Beulah in July and August, and Pro- 

 fessor Birge (Birge '97) has already noted that it is common 

 in the deep waters of the Oconomowoc lakes, which probably 

 should be classed with the small deep lakes. 



Bosmina. 



In Lake Winnebago I have not found Bosmina at all in the 

 months of July and August. In 1899 it did not appear until 

 the first of December, and very few were found in the winter 

 months. There was a very large increase about the first of 

 June. Then it abruptly disappeared and reappeared the last 

 of September. There was a fall maximum the first of Novem- 

 ber, and then a rapid decline. During the winter months there 

 were very few, and no marked increase until the first of June, 

 1901, when there was an increase corresponding to that of the 

 preceding year. It then disappeared and was found again the 

 first of October, when it commenced to increase with great 

 rapidity. 



In Green lake, as shown by the curves (Plate XVII) Bos- 

 mina occurs at all times of the year. Comparing these curves 

 with the curves in my former paper (Marsh '97) it would ap- 

 pear that we may expect Bosmina to have a fall maximum 

 in November or December. After this maximum there is 

 a sharp decline and the number then grows gradually smaller 



until June or July, when generally there is a slow increase 

 3 



