58 PLANKTON OF WINNEBAGO AND GREEN LAKES. 



plankton is the vegetable material. This is especially true in 

 shallow lakes in which the Crustacea form', relatively a much 

 smaller part of the plankton than they do in the deep lakes. 

 The conclusions which I reached in my former papers were very 

 largely derived from work on Green lake, in which the Crus- 

 tacea are more abundant than in Lake Winnebago, not only rel- 

 atively to the vegetable organisms, but absolutely. It would 

 follow that aggregations of Crustacea would affect the total 

 plankton much more in the deep lakes. In lakes like Lake 

 Winnebago Crustacea seldom form a controlling part of the 

 plankton except when large numbers of certain of the cladocera 

 are present, and then the total may be appreciably affected. 

 For instance, in the collections listed for July 10, '99, the 

 larger totals were caused by the presence of Eurycercus which 

 was present in unusual numbers, and the evidence from my col- 

 lections seems to show that Eurycercus occurs in moving aggre- 

 gations or swarms that perhaps move under the influence of 

 slow currents. 



The collections from the deeper lakes, like Green lake and 

 Stone lake, show greater differences when taken on the same 

 day at different localities than do the collections from shallow 

 lakes. In these deeper lakes the Crustacea form) a larger pn>- 

 portion of the plankton. 



My conclusions then are as follows : 



1. I must acknowledge that the uniformity of horizontal dis- 

 tribution is greater than I had formerly supposed. 



2. Variations in uniformity, when general conditions remain 

 the same, are largely due to variations in the numbers of Crus- 

 tacea. 



3. Inasmuch as Crustacea in deep water lakes are not only 

 more abundant relatively to the plants, but are absolutely more 

 numerous, it follows that the horizontal distribution of the 

 plankton in deep water lakes will be less uniform than in shal- 

 low 1 water lakes. Large variations in the horizontal distribution 

 of the plankton in shallow lakes will only be noticed, under ordi- 

 nary conditions, when, for some reason, there is a local aggre- 



