ANNUAL DISTRIBUTION OF THE ORGANISMS. 19 



the last of July, in 1899 its greatest development was early 

 in October, and in 1901 it reached a maximum about the mid- 

 dle of September. The total production in 1901 was much 

 greater than in the preceding years. 



Codonella lacustris Entz. -riv^F w 



Codonella- does not occur in Green lake. In Lake Winne- v^* 

 bago it is found most abundantly in the winter months, 

 although it occurs at other times of the year. It is never pres- 

 ent in sufficient numbers to affect the total plankton. 



Epislylis galea Ehrenberg. 



Eyistylis was found in small numbers in the plankton 0^. 

 Lake Winnebago in the fall of 1900 and 1901. 



I found it also in the plankton of Birch lake in August, 1900. 



Anuraea cochlearis Gosse. 



• Anuraea cocUearis is ted at all times of the year in both *fc H 

 lakes. There is no uniform maximum period. Apstein states 

 for Ploner See that the greatest numbers are found in July. 

 Seligo finds for various lakes maxima in May, June, July, and 

 September. 



The largest single collection in Green lake was made in Au- 

 gust, while the largest collection in Lake Winnebago was made 

 in January. The occurrence of the species, however, was very 

 erratic, and I can draw no conclusions as to its annual period- 

 icity. 



Anuraea aculeata Ehrenberg. 



Anuraea- aculeata was found in Green lake only in two col- 

 lect inns, — in July and December, 1901, and then in very small 

 numbers. In Lake Winnebago it was pretty constantly in the 

 plankton from October or November until the next May. The 

 largest single collection was in January, 1900. Thus Anuraea 

 aculeaia would appear to be a distinctly winter form. This 

 agrees with the statements of Seligo and Voigt, but Apstein 

 has found it a summer form. 



