Table 71 shows the two-year mean counts of Copepoda, nauplii, and 

 Cladocera for the period from late May to early October, inclusive. 

 Only the four most numerous genera of adult Crustacea are included. 

 For each lake the copepods include Diaptomus and Cyclops; the 

 Cladocera include Daphnia and one other genus. In Lake Erie the 

 second ^enus is Diaphanosoma; in Lake Mendota and Lake .i/innebago it 

 is Chydorus; and in Green Lake, Bosmina. The figures would be affected 

 very little by the addition of the rarer forms, such as Epischura, 

 Limnocalanus, and Leptodora. Both Birge and Marsh recorded their 

 results in numbers per square meter of surface, and these have been 

 changed to the number per liter by dividing by the depth of the 

 sampling station in meters, and again by 1,000. For Lake Mendota 

 this was 18 meters; for Lake //innebago it was assumed to be 5 meters, 

 and for Green Lake, hS meters. 



The data given in Table 71 need not be discussed in detail. 

 It is evident that Lake Mendota had the highest mean number of 

 Crustacea (nauplii were not counted), and that Green Lake had the 

 least. This finding is to be expected, for eutrophic lakes are, in 

 general, much richer in plankton than oligotrophic lakes when they 

 are compared on a per unit volume basis. The counts for the Island 

 Section are lower than those for Mendota, but higher than those for 

 Green, and, since Mendota and Green are fairly typical of their 

 classes, it may be concluded that the Island Section stands between 

 the plankton-rich and the plankton-poor lakes. In the absence of 

 an exact measure of richness, it might be described as "moderately 

 rich" in plankton Crustacea. It is of considerable interest to note 

 that the Island Section had counts closer to those of Winnebago, 

 which it resembles hydrographically, than to those of the smaller and 

 deeper lakes. 



Portage River Section 



Samples were taken from only one station in the Portage River 

 Section. This was Station l59, located l/ii mile straight out from 

 the river's mouth. Conditions here are subject to marked changes due 

 to the influence of littoral ciirrents and intermittent discharge 

 from the river itself. We should expect marked changes in the abundance 

 of the various plankton organisms in such a situation, and a special 

 investigation would be necessary to determine the effect of the numerous 

 factors involved in the changes. The data collected here in 1929 and 

 1930 are shown in Table 72. It would be idle to attempt to discuss 



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