ON THE LIMNETIC CRUSTACEA OF GREEN LAKE. 



BY C. DWIGHT MARSH, 



Professor of Biology in Ripon College, 



WITH PLATES V TO XIV. 



The investigations on which this paper is based were com- 

 menced in August, 1893. At that time I constructed a vertical 

 net, which could be closed at any depth. With this net I made 

 twelve series of five meter hauls in a little more than twenty- 

 four hours. My object was to determine the facts in regard to 

 the diurnal migration of limnetic Crustacea, — a migration which 

 I was certain, at that time, took place. The material obtained 

 in these collections was carefully counted, the results tabulated, 

 and reduced to percentages, and a report on the subject was 

 made at the summer meeting of the Wisconsin Academy, in 

 June, 1894, and a brief resume was published in the American 

 Naturalist in the same year. 



So far as difference of diurnal distribution was concerned, the 

 experiments gave only negative results, but certain facts in 

 regard to the general vertical distribution of the different 

 species came out very clearly. It seemed to me probable, bow- 

 ever, that the distribution might not be the same on different 

 days, and, in all probability, would differ greatly in the differ- 

 ent seasons. At that time, very little had been published 

 in regard to the occurrence of the entomostraca in different 

 seasons. It seemed to me that if a systematic series of collec- 

 tions could be made throughout the year, the results would be 

 very interesting. The matter was brought to the attention of 

 the trustees of Ripon College, who recognized its importance, 

 and made a special appropriation to pay the necessary expenses 

 of the investigation. 



