30 PLANKTON OF WINNEBAGO AND GREEN LAKES. 



the year with two pronounced maxima, one in the spring and 

 one in the summer or early fall. In the summer of 1899 the 

 summer increase was distributed from July to December, with 

 no great rise at any time. In the summer of 1901 there was a 

 single maximum in the middle of July, while in 1902 this 

 maximum did not come until the first of September. In the 

 spring of 1900 there was, about the first of April, the largest 

 number found at any time in the whole period under observa- 

 tion. In the next year, 1902, the maximum came about the 

 middle of June. 



It is extremely difficult to correlate these curves with those 

 of the mature copepods. The summer increase is doubtless 

 largly composed of Diaptomus oregonensis and Cyclops brevis- 

 pinosus, with some specimens of Cyclops Leuckarti and Epis- 

 chura. A comparison of the summer curves of these species 

 shows a very close relation with the curves of larvae. The win- 

 ter larvae are probably entirely of Cyclops pulchellus. The 

 spring maximum is composed of the three species, Cyclops 

 Leuckarti, Cyclops pulchellus, and Dwptomus oregonensis. 



In Green lake the curves resemble in general those of Lake 

 Winnebago, with the exception of the marked increases in the 

 winter months. In the three summers under observation there 

 was a single maximum coming in the successive years in July, 

 August, and September. I know of no reason why there should 

 have been this difference. In the summer the larvae probably 

 belong to all the species of copepods except D. sicilis, Limno- 

 calanus, and Episcliura. The rises in the winter months are 

 due largely to the two latter forms. I have found larval E pis- 

 chum only in February and March. The increase in October 

 and November is because of the coming in of Diaptomus sicilis. 



The rise in the curve in May and June is doubtless largely 

 due to the increase in D. minutus, which later forms one of 

 the chief elements in the plankton. 



Diaplianosoma brachyurum Liev. 



Diaphanosoma is distinctively dependent for its development 

 upon the high temperature of the summer months. In Lake 



