500 cubic centimeter samples. Samples of that size would be expected 

 to show inequalities in distribution. V/ilson's data were based 

 entirely on horizontal hauls and hence their adequacy is open to serious 

 question. Southern and Gardiner, in a series of carefully planned 

 experiments involving both vertical and horizontal hauls, were able to 

 show marked irregularity in the distribution of the Crustacea of 

 Lough Derg. However, they called attention (p. lUh) to a number of 

 special conditions which tend to operate against uniform distribution 

 in that lake. Somewhat similar conditions exist in Bodensee, studied by 

 Bayersdoerfer, 



Even the most confirmed proponents of the idea of uniform 

 distribution do not argue for absolute uniformity, and no one expects 

 to detemiine the number of organisms per unit volume with absolute ac- 

 curacy. While Birge (I898, pp. 366-37$) was able to show irregularities 

 in distribution and to observe swarms with the unaided eye, his data on 

 seasonal distribution show such regular trends and such close agreement 

 in the different years for certain forms that there is no doubt regard- 

 ing their adequacy. His results prove that it is easily possible, for 

 Lake Mendota, and probably for most inland lakes, to take samples fre- 

 quently enough to eliminate the errors arising from unequal distribution. 



Large and consistent inequalities in horizontal distribution 

 were found between the different sections of Western Lake Erie, as will 

 be pointed out in later pages. There were also inequalities noted 

 within the Island Section but they appeared to be fortuitous. It 

 appears unnecessary to present the available data on horizontal dis- 

 tribution in this section of the lake. An attempt was made to avoid 

 errors from that cause by taking samples -from several stations r&ther 

 than from one. The adequacy of the sampling program will be discussed 

 in later pages. 



Vertical distribution 



Lack of uniformity in the vertical distribution of plankton 

 organisms was noted very early, even before the introduction of 

 Hensen's quantitative methods. It was noted also that certain of the 

 Crustacea were more abundant at the surface at night than in the day- 

 time, indicating a diurnal vertical migration, A review of this subject 

 has been published by Kikuchi (1930), In the present investigation, all 

 of the samples were taken during the day-time, and hence the data are 

 incomplete with regard to vertical distribution. Because of this in- 

 completeness, it has been considered sufficient to present only a small 



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