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February, March, and April have been covered by collections 

 at intervals of five days or less, and from July 14, 1897, to March 

 28, 1899, a period of nearly twenty-one months, the series of 

 regular weekly collections is almost unbroken. The following 

 table gives the distribution of the collections by months in the 

 several years. 



DISTRIBUTION OF COLLECTIONS BY MONTHS. 



The distribution by months is such that a fair basis is 

 formed for the determination of the seasonal fluctuations, 

 since every month is represented by a considerable number of 

 collections. The larger numbers in the summer months re- 

 sult from the fact that the field station was always open dur- 

 ing this season. The total number, 235, is more than twice 

 that made at any other station in our field of operations, and 

 affords the most complete and longest series in our collections. 

 It is fitting that in this our most variable station the interval 

 between collections should be least. The total period covered 

 by our collections here is a little over fifty-seven months, and 

 the average interval between collections 7.4 days. I know of 

 no series of quantitative plankton collections, in any waters, of 

 equal range or time, variety of season, and brevity of interval. 



THE LOCAL DISTRIBUTION OF THE PLANKTON AND ITS RELATION TO THE LIMIT 

 OF ERROR IN THE METHOD. 



The investigator of plankton problems is constantly con- 

 fronted by the question of the extent of the error resulting 



