26 PLANKTON OF WINNEBAGO AND GREEN LAKES. 



Limnocalanus macrurus Sars. 



Limnocalanus only occurs in deep lakes, so it is not found at 

 all in Lake Winnebago. In Green lake it is found at all times 

 of the year. In my former paper (Marsh '97) I stated that 

 its maxima were in May and November. The curves from the 

 present series of observations (Plate VI) seem to confirm the 

 former results, although the spring maximum occurs as early 

 as April in some years, in others as late as June, and in the 

 summer of 1900 the greatest number during the year was in 

 July, although there had been a marked rise in April. Dur- 

 ing the winter months most of the individuals are larval forms. 



It will be noticed that the maxima of Limnocalanus are not 

 very widely different from the smaller numbers found at other 

 times. This is doubtless due to the habits of this species, 

 which, as I have shown before, prefers a low temperature of the 

 water, and during the summer months is found to very little 

 extent above the thermocline. In the winter it is found at all 

 depths. While, for the sake of the lower temperature, it suc- 

 ceeds in adapting itself to the stagnant conditions of the deeper 

 waters of the summer, it does not flourish at that time as it does 

 when, the temperature being favorable, it can find a home at 

 any depth. 



Cyclops brevisplnosus Herrick. 



C. brevispinosus is found in both Green lake and Lake Win- 

 nebago. The curves (Plates VII and VIII) show that it 

 should be ranked as a summer form, although it may be found 

 at all times of the year. In the three summers under observa- 

 tion there was a marked increase the latter part of July or the 

 first of August. In 1902, however, the greatest number of the 

 year was found about the middle of September. 



In Green lake apparently there may be expected a great in- 

 crease in the latter part of June or in July. In December, 

 1902, however, I took the largest collections of the whole pe- 

 riod of two and a half years. These results correspond with 

 the results reported for Green lake in my former paper (Marsh. 

 '97). 



