part of the available data; enough to show the usual distribution of 

 the more important plankters in the day-time, and some of the variations 

 encountered. In Table 6? are shown all of the data taken at 

 Station 37A in 1930 for Diaptomus, Cyclops, nauplii, Daphnia, and 

 Rotifera. 



The data presented in Table 6? need not be discussed in detail. 

 The folloiiiing summary, based on these and many other data, should 

 suffice. During the day-time the leading groups of adult plankton 

 Crustacea (Diaptoraus, Cyclops, and Daphnia) usually avoid the upper 

 half meter of water, and concentrate in the middle depths; they are 

 usually rare near the bottom but less rare than at the surface. 

 The nauplii are much less consistent in their distribution than are 

 the adult copepods. In general they appear not to avoid the upper 

 water; but frequently they are found in largest nujnbers near the 

 bottom. In a large niimber of cases they are foimd concentrated at more 

 than one level. The rotifers also are inconsistent and often show con- 

 centration at more than one level. The remaining groups of plankton 

 organisms are too rare to permit a positive statement with regard to 

 their vertical distribution. 



Seasonal distribution 

 Season of 1928 



Plankton studies with the vertical closing net were begun on 

 May ill in 1928, and discontinued on November 20, No samples were taken 

 during the last two weeks of August or the first two weeks in September. 

 The samples were taken at a large number of stations which were well 

 distributed over the Island Section. The results will be discussed in 

 less detail than those of 1929 and 1930 because they vzere obtained 

 with a relatively unreliable type of apparatus, and because of the break 

 in the record during late August and early September. 



Seasonal distribution of the four principal groups (Diaptomus, 

 Cyclops, Daphnia, Diaphanosoma) is shown in Table 68. Each month of the 

 period studied was divided into two periods of approximately two weeks, 

 with minor exceptions noted in the first column of the table. The mean 

 date of sampling for each period is given in the second column. The 

 third coliimn gives the number of stations used in determining the mean 

 nurober of organisms for each period. 



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