122 



straining part was made of Dnfonr's No. 2(i lioltiiiii- cloth, were used. 

 Tlie quantity of water strained for a catch was the amount produced by 

 forty strokes of the pumi*, which averaged 2'2.~) liters. 



The counting method was used to determine the relative abundance 

 of the various plankton forms. In most cases 20 per cent, of the material 

 obtained in a catch was coimted, and the results thus obtained for the 

 various forms were multiplied l)y live in onb'r to determine the numl)er 

 of individuals in a whole catch, ^^'henl•ver a catch contained a compara- 

 tively small number of individuals, for example, the catches near the 

 surface in day time, the whole catch was counted. Also, ;\11 the indb 

 viduals of the hirger forms, such as p]pischin-a and Leptialoi'a, which are 

 readily recognizable with tlie naked eye. were counted. 



The sets of observations may li(> divided iiili) five groups: 



1. Twenty sets of day catclies which wvvr made not earlier than '.) 

 a. m., nor later ttian 4 p. m. 



2. Six sets of night catches which, wilh one exception, wei'c niadi' 

 between 9 i). ni. and midnight. On Septembci' 2. a sei-ies was macb' as 

 early as 8 p. m.. Iiut this, however, was an hour and ;i h.ilf after sunset. 



3. Four sets of evening catches were ma(b'. These were begun short- 

 ly before sunset and continued ;it lialf liour intervals .-in hour or more 

 after sunset. 



4. The morning obsei'vations were begun one and a half to two hours 

 before sunrise and were continU(Ml at thirty minute interv,\ls until after 

 smu'ise. Six sets of these were made. 



5. In Aiignst there were two sets of observations in which catches 

 were made at the surface at regular intervals during the entire night. 

 Both series were begun before sunset and continut'd until after sunrise. 

 Catches Avere nuule at half hour intervals until S and '.) p. m., respective- 

 ly, then every hour until ■"> and 4 a. m.. respectively, and again at half 

 Ikhu- int(>rvals mitil after s\nu-ise. The residts of these observations are 

 sliov.n in Figs, 1 to 4. 



The tirst and second groups covered the entire depth of tlu^ lak(> 

 (twenty-five meters), while the catches of the third and fourth groups 

 were contined to the upper four meters. The fifth gioup consisted of 

 surface catches. 



