422 Birge — Vertical Distribution of Pelagic Crustacea. 



to me by Messrs. Harder and Olson, and have been re- worked 

 by myself and put into final shape for publication. Each gentle- 

 man reported upon the species investigated by himself. A large 

 amount of detailed work was done, especially by Mr. Olson, 

 which does not appear in the following paper. No attempt has 

 loeen made to offer the results of each set of observations. The 

 value of statistical work of this kind lies rather in the average 

 results obtained than in the record of each single observation. 

 It is believed that the use to which this paper may be put does 

 not warrant the printing of the very numerous detailed com- 

 putations. They are, however, preserved, and can be referred 

 to by any person who is interested in the subject. 



The original purpose of the investigation was to determine 

 'the supposed diurnal migrations of the Crustacea, but since the 

 results in this direction have been entirely negative, the out- 

 come of the work has been to give us a definite idea of the ver- 

 tical distribution of the Crustacea in the lake during the month 

 of July. This may be called their summer position, for it 

 should be expressly noted that this position is not a constant 

 one during the different seasons of the year. The conditions of 

 July apparently obtain through August and the greater part of 

 September, but later in the year a totally different and more 

 uniform scheme of distribution is developed. The conditions of 

 the later spring and of June are not yet known. — E. A. B. 



LAKE MENDOTA. 



Lake Mendota, in which these observations were made, lies 

 immediately to the north of the grounds of the University of 

 "Wisconsin, which extend for a mile along its southern shore. 

 The greatest length of* the lake is about 6 miles from east to 

 west, and its greatest breadth is something under 4 miles. It 

 is partially divided into two basins by points on the east and 

 west shores, which leave between them a space of about two 

 miles. The smaller or southern basin is about 3 miles in 

 length. With the exception of these projections the lake is 

 •quite regular in form, being without islands and having only 

 broad bays with wide mouths. The conditions of life, therefore, 

 ;are substantially uniform throughout the lake. 



