24 University of California Publications in Zoology [Vol.22 



27 in the median line of the cell. The whole count was completed by 

 running over exactly half of the cell looking for strays and for a check 

 on larger organisms which might be irregular in distribution. After 

 a year's experience the writer is inclined to think that twenty-five or 

 thirty fields would be sufficient for the detailed count in view of the 

 half-slide check. At any rate he is satisfied that the possibility of 

 error in counting will rest elsewhere than on the method of selecting 

 areas for counting. It might be said too, that the year's experience 

 indicates that the method of filling the cell gives as uniform distribu- 

 tion of plankton in the cell as can be hoped for in any case. 



The method of recording the count was almost uniform. Mrs. 

 Allen sat near the microscope and wrote down names or made check 

 marks as the names were called. In two or three cases about half the 

 catch was recorded by the writer while himself counting. On about 

 ten occasions he recorded as much as ten fields in like manner. These 

 were the only exceptions. Occasionally the writer called the name of 

 one planktont when another was intended, the mistake being noticed 

 because it did not sound right. It is altogether probable that some 

 such mistakes were made which were not noticed. In addition to this, 

 of course, we must recognize the presence of clerical errors not humanly 

 avoidable in such a mass of material. It can only be said that all 

 reasonable precaution has been taken to avoid them. 



Computation and Tabulation 



After recording, the counts were computed for a full cubic meter, 

 and then tabulated by key sheets, such as suggested by Professor 

 Kofoid in his Illinois report. Prom these sheets they were finally 

 transferred to the statistical tables. 



Identification or Forms 

 Identification of species, or even genera, was very difficult in 

 many cases. This was due to several conditions. First, the preserved 

 planktont was often very different in appearance from the living speci- 

 men. Second, many kinds had very marked tendency to coherence 

 or agglutination in formaldehyde. Third, many of the smaller organ- 

 isms were hidden wholly or in part by silt or by larger organisms. 

 Fourth, many different organisms have the same appearance in very 

 young stages; they also resemble mature stages of simpler forms. 

 Fifth, distinctive characters were frequently invisible in the position 

 found in the Rafter cell. Sixth, many forms were not sufficiently 



