APPENDIX: VALIDITY OF METHOD 5°9 



the Recorder (Type I) being fitted with a 3 in. diameter opening as compared with 

 the 1 1 in. opening of the Indicator. However, a comparison of the results is not without 

 interest. The variations in the numbers of the four predominant species of Copepoda 

 and the total phytoplankton obtained by the Recorder are shown in Fig. 31 as con- 

 tinuous line curves together with the indicator results as histograms in their relative 

 positions along the line of traverse. The positions of the twenty-six indicator samples 

 (each one mile tow) are shown by the letters A to Z to distinguish them from the posi- 

 tions of the recorder sections (each taken over 3-5 miles) numbered 23 to 33. The re- 

 corder run ended at section 33 ; the earlier part of the record before section 23 is not 

 figured. Now it has been shown in the main part of the paper, p. 495, that a section of 

 the recorder roll samples not only the plankton of the unit of distance (in this case 

 3-5 miles) travelled by the machine as a division winds across the water tunnel, but also 

 a fraction of the preceding and following unit of distance. Calculations have been made 

 on this basis to render the results from the Indicator as closely comparable as possible 

 with those from the Recorder and the result is shown in the diagram as a broken line. 

 This result is probably rendered less reliable on account of the loss of the samples 14 

 and 18 (N and R) which for purposes of the calculation were given values based on an 

 average of the two adjacent samples, but which in reality may have varied markedly 

 from them. In spite of the difference in the depth of the two instruments the general 

 increase in the numbers of Calanus, Pseudocalantis, and Temora over the recorder sec- 

 tions 27 to 31 is well confirmed by the indicator samples, as also is the fall in numbers at 

 the end of the record if the histograms are followed (the calculated broken line cannot 

 be extended beyond section 31 because at section 32 the Recorder is sampling also 

 fractions of the area which extends beyond the last of the indicator samples). The corre- 

 spondence between the Calanus curves, in spite of the loss of the samples iV and R, is 

 particularly close. The Acartia result shows a marked difference probably due to the 

 difference in depth distribution. The zone of phytoplankton abundance shown by the 

 indicator samples corresponds with the peak of abundance in the recorder record, but 

 here again difference in depth may likely account for the difference in general distribu- 

 tion. Near the surface the Indicator reveals a dense concentration of phytoplankton at 

 samples 1 to 8 (A to H) and but little beyond ; at 10 m. depth the Recorder shows much 

 less but more widely spread. 



A brief note may be added on the distribution of the phyto- and zooplankton. If 

 considering indicator samples alone, it might be thought that the increase of zooplankton 

 away from the phytoplankton zone might be explained simply as an increase caused by 

 vertical migration bringing more of the animals into the path of the Indicator with the 

 passage of time towards night. A time scale is shown in hours in Fig. 30. But now re- 

 ferring to the recorder graph we see that there were also larger numbers of the same 

 species of Copepoda before the patch of phytoplankton was encountered, i.e. earlier in 

 the afternoon. It would appear then that here is further evidence of the inverse dis- 

 tributional relationship between phyto- and zooplankton discussed in Part v of the 

 report (Hardy and Gunther, 1935) already referred to in the main paper. 



