?3 8 DISCOVERY REPORTS 



The present study was suggested by Dr N. A. Mackintosh, C.B.E., who has given me advice and 

 guidance during the whole time I have been engaged on it. 



I should like to thank both Dr J. H. Fraser, F.R.S.E., who has read and corrected the typescript 

 and given me a great deal of valuable advice during the preparation of this paper, and Dr H. E. Barg- 

 mann who read the first draft and made many helpful suggestions. 



Mr E. Childs has assisted me in sorting a number of the samples required for this work, and my 

 colleagues, Mr P. Foxton and Mr A. de C. Baker, have drawn my attention to any interesting 

 specimens which they found while they were engaged upon work on the Discovery collections. 



I wish to thank Professor T. Tokioka of the Seto Marine Laboratory, Japan, for kind permission to 

 reproduce two of his figures (Figs. 9 and 13); Walter de Gruyter and Co. of Berlin for permission to 

 reproduce four of Ritter-Zahony's figures (Figs. 1 and n) from the Deutsche Siid-Polar Expedition 

 Report; A. H. Pettifer of the Government Printing Office, Sydney, N.S.W., for permission to repro- 

 duce one of Johnston & Taylor's figures (Fig. 2) from the Australasian Antarctic Expedition Report ; 

 and the Council of the Linnean Society for permission to reproduce two of Fowler's figures (Figs. 3 

 and 4) from the Report on the Biscayan Plankton of H.M.S. 'Research'. 



METHODS 



All the material used in this investigation came from plankton samples in the Discovery collections. 

 Most of the samples were taken from stations worked in the Southern Ocean, but in order to confirm 

 that <S. gazellae is confined to this area, the field examined was extended where possible by examination 

 of tropical and subtropical stations. 



It was the practice on board ' Discovery II ' to make both vertical and oblique hauls at each full 

 station, mainly with closing nets. (There are a number of stations at which only one or two nets were 

 used, and some also at which plankton nets were not used at all. This accounts for many of the serial 

 numbers ' excluded ' in Tables 1 and 2.) At the great majority of full stations samples were taken with the 

 standard 70 cm. vertical nets (N70V) from six or seven depths: 50-0, 100-50, 250-100, 500-250, 

 750-500, and 1000-750 m. ; and on a good many occasions (especially on lines of stations on the 

 o° meridian) a haul from 1500 to 1000 m. was added. Except when this series was curtailed on account 

 of bad weather or shallow water, the vertical nets covered a much greater range of depth than the 

 oblique nets (N 100 B and N70B), which were normally towed through approximately 100-0 m. and 

 occasionally also through deeper horizons. The oblique nets, however, usually take larger samples. 

 Occasionally deep 2 m. and 4^ m. nets were used, and in many cases the resulting samples have been 

 examined for S. gazellae, but owing to the irregularity with which these hauls were made, in time, 

 position and depth, the material so obtained was only of use in anatomical comparisons. 



For certain aspects of this work samples from a particular series of nets alone were examined, e.g. the 

 vertical 70 cm. nets were used for the section on vertical distribution, but for other aspects, where it was 

 necessary to obtain as many specimens as possible, all nets from any appropriate station were examined. 



At the outset of this study a great deal of data were already available. These consisted of counts of 

 S. gazellae present in the oblique 1 m. net hauls which had been analysed from time to time, and also 

 in the 70 cm. vertical net hauls from lines of stations which had been repeated at different times of 

 year in the meridian of 8o° W. More detailed information was also made available through the 

 kindness of Mr Marr who studied the Chaetognatha during the commissions of the ' Discovery II ' 

 in 1931-33 and 1935-37. These data consisted of measurements and numbers of chaetognatha from 

 the 1 m. oblique nets (commission of 1931-33) and 70 cm. vertical nets (commission of 1935-37), 

 and included notes on food, and observations on the state of maturity. 



