136 DISCOVERY REPORTS 



Table VIII. This table shows the average number of warm- and cold-water species per 

 haul for each line of stations. On some of the lines none of the stations was taken in the 

 middle of the night, and consequently the diurnal variations of some species prevent a 

 reliable estimate of their numbers. A query is inserted where a species is absent but 

 might have been taken if there had been a haul between the appropriate hours at night, 

 and "Present" is inserted where a few were actually taken but where a larger number 

 might be expected in a night haul. 



In these waters the moderately "cold" species (group (g)) play a part corresponding 

 to that of the very "cold" group in the high latitudes. As in other regions, the figures 

 here show a diminution in the proportion of cold-water species as the summer advances. 

 A glance at columns 1 and 2 shows a much "warmer" plankton in April than in 

 February 1927-8. In the 1928-9 season the warm- water species were quite well 

 represented at the August stations, as they were in September off South Georgia, and 

 the "coldest" plankton is found in December, i.e. early in the summer. In February, 

 March and May there is a general reduction of cold-water species and an increase in 

 nearly all the warm-water species. In the 1929-30 season the "coldest" plankton, as 

 we should expect, is taken in November. The cold-water species mostly disappear in 

 March and April, though a specimen of Sibogita unaccountably appears in March. Of 

 the warm- water species Heterorhabdus sp., Euphausia triacantha, Pleuromamma, Pareu- 

 chaeta, Parathemisto and Euphausia frigida increase towards the end of the season. 

 Others are irregular and Eucalanus is more plentiful in November. In the 1 930-1 

 season stations in this area were taken only in March, but it will be seen that the catches 

 include slightly more cold-water species than those of March 1929-30 and 1928-9. 

 We should expect this in view of the fact that the 1930-1 season was a specially 

 cold one. 



It is now clear that over the area covered by the investigations, wherever it is possible 

 to compare observations taken at different times of year, the plankton at a given point 

 has a larger element of cold-water species at the beginning of the summer (November 

 and December) than it has later on. It seems also certain that in unusually cold seasons, 

 such as 1930-1, the cold-water species have a tendency to persist in relatively low 

 latitudes for a longer period than they would in a normal season. The stations taken in 

 August and September 1928, suggest that the relatively "warm" plankton, found at the 

 end of the summer, persists throughout the winter. There was at that time a thin plankton 

 composed only of the warm-water species in proportions resembling those of the 

 previous season. It is highly probable that the plankton undergoes little change from 

 March or April or through the winter, remaining as a slowly diminishing population 

 until the spring, when there is an invasion of cold-water species and a development of 

 the rich summer plankton. There seems to be an increase in the proportion of warm- 

 water species as the summer goes on, but this is not quite so clearly defined as the dis- 

 appearance of the cold-water species. 



The gradual change from a cold- towards a warm-water plankton does not of course 

 imply a southerly drift of the Antarctic surface water during the summer. It is quite 



