I9 8 DISCOVERY REPORTS 



as Jacobsen & Paulsen (1912) found, for small samples this error is very small. This is also shown by 

 the results, given in Table 1, of ten repeated measurements on samples from St. 2414. The variations 

 in the measurements that occur at each depth in no way detract from the main conclusions to be 

 drawn from this particular set of data, namely, that the bulk of the plankton is concentrated below 

 250 m., the upper 100 m. being relatively poor in plankton (see Fig. 2). 



Table 1. The results of ten repeated measurements (in cc.) of the volumes of samples from St. 2414 





The rather crude method of ' drying ' the plankton on blotting paper is thus a convenient method of 

 reducing such errors to a minimum. While the basic method of measurement remained the same 

 throughout this work the procedure outlined above had to be variously modified when dealing with 

 many Antarctic spring and summer shallow samples containing phytoplankton. This paper is concerned 

 only with the variations in the standing crop of zooplankton, so that it was necessary to separate the 

 animals from the phytoplankton and measure their volume separately. No standard treatment was 

 possible, since among such samples there was every gradation from those rich in zooplankton and 

 poor in phytoplankton to those in which phytoplankton predominated. Where there was only a trace 

 of phytoplankton no attempt was made to separate it from the zooplankton, since it was considered 

 that the amount was so small as to be immeasurable by the displacement method. Other samples, 

 though rich in phytoplankton, contained only a few relatively large animals which could easily be 

 picked out for separate measurement of their volume. The most difficult samples to deal with were 

 those rich in phytoplankton and both adult and larval zooplankton organisms. To pick out the animals 

 would be a lengthy and difficult task, and it is doubtful whether the result would be commensurate 

 with the effort. The method adopted for a sample of this kind was to dilute it with water and pour it 

 into a large glass funnel having its stem closed by a large-bore glass tap. The zooplankton, by virtue 

 of its faster rate of settlement, collects at the bottom of the funnel, from which it can be run off via the 

 tap, and measured by the standard method, after which it is preserved again with the phytoplankton. 

 This method has the same disadvantage as the method of picking out the animals, namely, that some 

 of the smaller forms remain in the phytoplankton and are not measured. It was considered, however, 

 that as these are such small forms, the inaccuracy due to their omission from the final volume would 

 not be great enough to influence any conclusions drawn from the result, the main thing being to get 

 the best possible measure of the zooplankton volume alone rather than to measure the sample as a 

 whole and thereby to introduce a considerable error due to inclusion of the phytoplankton. A few 

 samples (23) defied all attempts to separate the animals, and these were not measured. Shallow hauls 

 rich in phytoplankton are noted in Tables 1 1 a-f in the Appendix 





