METHODS , 9 



(a brass sliding weight of special design) down the wire to operate the first closing 

 mechanism which in turn released a second messenger to slide down the wire to close 

 the bottom net. The actual times of closing were noted by placing a hand on the towing 

 wire and feeling the shock of the messenger striking the closing mechanism. This series 

 of N ioo H nets was immediately followed by a similar series of N 70 H nets towed and 

 closed in exactly the same manner except that the length of tow was \ mile. This opera- 

 tion completed a full routine station. 



At horizontal routine stations only the above procedure with the N 100 H and N 70 II 

 nets was carried out. 



The samples collected were taken to the laboratory, poured into glass jars, treated 

 with formalin, labelled and allowed to settle. Formalin was added as soon as possible 

 to these quantitative samples, otherwise if the sample contained a large number of 

 carnivorous animals, such as Hyperiid Amphipods, its composition might be materially 

 altered after a little time. When the sample had settled the excess fluid was filtered off 

 and the bulk reduced to a convenient size for storage in small jars or tubes. Any or- 

 ganisms remaining on the filtering silk, which in all but the N 50 V samples was of a 

 finer mesh than that used in collecting, were washed off into the sample. 



When heavy catches of the larger organisms, such as Salps, Euphausians and Para- 

 themisto, were taken, making the sample of unreasonable size, only a small fraction of 

 the total would be kept: those thrown away were counted and their number recorded. 



Whenever possible a preliminary examination of the sample would be made, together 

 with an approximate estimate of its volume. At times, however, on account of the 

 heavy rolling of the ship in these latitudes or lack of time, when stations followed one 

 another in quick succession, not more than a cursory glance at the material could be 

 taken. This is regrettable, but unavoidable when one is working at high speed to get 

 through an extensive programme before another period of bad weather sets in. It is 

 regrettable because when one comes to examine the samples in greater detail one often 

 wishes one had just one more sample for confirmation or had altered the course of the 

 ship a little or had extended the line of observations just a little farther on: the oppor- 

 tunity has gone for ever. It is important that the intervals in time between stations in 

 a plankton survey should be as small as possible ; it is also important to learn as much as 

 possible of the results in the time available as one is going along. 



DESCRIPTION OF CRUISES UNDERTAKEN 

 The cruises during which the plankton samples were taken may be briefly described 

 in chronological order. Stations other than routine plankton stations will not be men- 

 tioned. The exact position of stations in latitude and longitude will not be given in the 

 text; these with date, time and sounding are given in the tables in the Appendix; 

 other details, including state of weather, sea and phase of moon, will be found tabulated 

 in the Station List, 1925-7, Discovery Reports, vol. I, together with the hydrological 

 observations. 



In February 1926 the 'Discovery' approached South Georgia from the north-east, 



