308 DISCOVERY REPORTS 



phytoplankton) as before. The other organisms, Parathemisto, Euphausia spp. adult and 

 larvae, and Salpa fusiformis, give a confirmation of the N ioo H results. 



Now in this series of N 70 H nets, towed horizontally and not covering the complete 

 range of diurnal vertical migration of some of the species, we again come against the 

 difficulty of there being a higher proportion of night stations in the range of phosphate 

 values between 90 and 100 than those above 100 or below 90. We can again divide them 

 into two series, one of daylight stations and one of night stations (taken between sunset 

 and sunrise). 1 Whilst we can take the same ranges of phosphate values in the daylight 

 stations as those in the daylight N 100 H stations, in the night stations, because the 

 times of the N 70 H nets differed slightly from those of the N 100 H, we must take 

 slightly different phosphate ranges to give an equal number of stations in each range. 

 We take the ranges above 98, 92-98 and below 92 (instead of above 97, 92-97 and below 

 92 as in the N 100 H), giving five stations in each range. The results are tabulated in 

 Table LIX. 



The daylight series gives a confirmation for each organism except Salpa, which is 

 known to be patchy , and is too large an organism to be caught adequately in the N 70 H nets. 

 The night series gives a 71 per cent confirmation, including that for Salpa, the excep- 

 tions not being in the range of low phosphate values (i.e. high phytoplankton) but the 

 reverse. Again, what is still more important is that the two series of day and night 

 stations offer two sets of quite independent results, one in general confirming the other. 



The results are interesting in that they suggest that our methods in the field sampled 

 the plankton very much more accurately than we had believed possible, in view of the 

 patchiness of some of the organisms. It is gratifying too that the methods of laboratory 

 analysis appear to have been adequate. It is perhaps worthy of mention that these 

 results which confirm each other have been obtained by three different workers — 

 Mr E. R. Gunther analysed the N 70 V nets, Mr Andrew Scott the N 70 H nets, and 

 Dr Helene Bargmann the N 100 H nets. 



The working out of the zooplankton results in respect to the N 70 nets of later 

 surveys has not gone far enough yet to offer any material for comparison, but 

 Dr Mackintosh has now completed the analyses of the N 100 nets for a number of later 

 surveys, and his results have recently been published (1934). At my request he kindly 

 plotted the more important organisms against ranges of phosphate values in the South 

 Georgia surveys of the seasons 1928-9, 1929-30 and 1930-1. The curves resulting from 

 these correlations show that in general there is a good degree of confirmation of our 

 results; but in a number of instances confirmation appears to be only moderate or 

 lacking, a closer analysis of the data must be undertaken before it is possible to speak 

 with certainty. 



In considering the results of these later surveys in relation to the one at present under 

 discussion it is necessary to note that an important change was made in the methods in 



1 This has not been done in the case of the N 70 V nets (Table LVII) because, except for the deeper 

 water species which occur in too small numbers to be so divided, the vertical nets cover the migration range 

 of the different species. 



