358 DISCOVERY REPORTS 



At present we can do no more than suggest that delayed spawning may be due to the 

 failure of the parent generation to reach maturity by the normal spawning time, owing 

 to external conditions such as temperature unfavourable to growth. 



GENERAL SUMMARY 



1. The foregoing paper is an account of the horizontal, and as far as possible the 

 vertical, distribution of the species Rhincalaniis gigas (Brady) in the Falkland Sector of 

 the Antarctic during the summer seasons 193 1-2 and 1932-3, and during the winter 

 months of the year 1932 around the Antarctic Continent. Some account of the life 

 history of the species, as far as it can be judged from the data available, has also been 

 given. The material upon which the paper is based consists of the catches from a large 

 number of hauls made with the i-m. stramin net in the Falkland Sector of the Antarctic 

 and around the Antarctic Continent during the 193 1-3 commission of the R.R.S. 

 ' Discovery II '. At every station from which the catches were analysed in this work the 

 i-m. net was towed from 250 to 100 m. approximately and from approximately 100 m. 

 to the surface. 



2. Rhincalaniis gigas is the dominant species in the copepod macroplankton, and thus 

 in the macroplankton generally, throughout a wide area of the Falkland Sector of the 

 Antarctic. In the season 193 1-2 it constituted over 75 per cent of the copepod catches 

 in Antarctic water flowing north-eastwards from the Bellingshausen Sea, around the 

 west coast of South Georgia, into the South Atlantic Ocean. In this water during the 

 season 193 1-2 over 10,000 individuals were taken in the upper and lower of the two 

 towings together. In the season 1932-3 the catches were smaller, and over 10,000 in- 

 dividuals were only taken at two stations, one in the Bellingshausen Sea current and 

 one in sub-Antarctic water between the Falklands and South Georgia. At the remaining 

 station the catches usually amounted to between 5000 and 10,000 individuals. R. gigas 

 constituted more than 75 % of the copepod catches in both Antarctic and sub-Antarctic 

 water in the Drake Passage in the season 1932-3 (pp. 294, 308, 313). 



3. The Weddell Sea is an area of scarcity of R. gigas, contrasting sharply with the 

 area of abundance in water of Bellingshausen Sea origin. In 193 1-2 R. gigas amounted 

 to less than 15 per cent of the total catch in Weddell Sea water where the average tem- 

 perature of the surface 100 m. was less than 0° C. (p. 296). In the season 1932-3 

 this species formed less than 25 per cent in Weddell Sea water, of which the average 

 temperature of the surface 100 m. was less than 0° C. and less than 15 per cent in water 

 with a temperature less than — i-o° C. (p. 313). In both seasons the total catches in 

 Weddell Sea water with a temperature below — i-o° C. amounted to less than 500 in- 

 dividuals in both nets. 



4. During the summer months the species extended north of the Antarctic con- 

 vergence in the Falkland Sector, but in the winter it became restricted to Antarctic 

 waters and the convergence formed the northward limit of its range so far as the surface 

 250 m. is concerned (pp. 298-301). 



I 



