CIRCULATION OF THE MACROPLANKTOX 381 



will be convenient to consider the more important of these species in the order of their 

 relative abundance in 8o° W. 



The distribution of Rhincalanus gigas is shown in Table IV and Fig. 5. Its vertical 

 distribution does not differ very much from that of the total organisms. The largest 

 numbers are usually near the convergence and the maximum concentration in summer is 

 between 100 and 50 m. Some very large catches were taken at this depth in March, but 

 included in these was a considerable proportion of immature specimens. In December 

 the vast majority were found in the surface layers as far south as 64 ° S. Beyond this 

 latitude the species was scarcer, and living mostly in the warm deep water, as if winter 

 conditions still prevailed in the higher latitudes. 



The numbers of this species have everywhere increased in March, especially in the 

 surface layers. Ommanney (1936) finds that it has a spawning period in late November 

 or early December in the Antarctic surface water of the Drake passage and western 

 Scotia Sea. This will account for the large catches in 8o° W in March. The proportions 

 of juveniles and adults have not been recorded, but large numbers of young forms were 

 noticed in some of the catches, notably at St. 13 17, 100-50 m., and these might well 

 have been hatched about December. Two other points are to be noted in the March 

 distribution. One is the comparatively large number of R. gigas now occupying the 

 Antarctic surface water south of 64 ° S, where the species was extremely scarce in De- 

 cember. The other is the development of a new centre of concentration in deep water to 

 the north of the convergence. The latter phenomenon we have noted in the section for 

 the total number of organisms. 



In September the numbers are in general reduced, but the species is almost confined 

 to the warm deep water, the largest quantity being at a depth of round about 500 m. At 

 this depth the deep water is at its warmest (see Fig. 3 c) and the southward movement no 

 doubt at its strongest. Moderate numbers occur even at depths below 1000 m. 



The stations in October were worked about six weeks after those in September. 

 During this period R. gigas had risen towards the surface again and we see the greatest 

 concentration as well as the nearest approach to the surface at St. 1447, just to the south 

 of the Antarctic convergence. Farther to the north and to the south the majority are still 

 at a rather lower level, and the numbers are less. 



In November also (only two weeks later) the largest numbers were taken on the south 

 side of the convergence. Farther south, and possibly farther north, the species seems a 

 little higher in the water than in October. 



This distribution of R. gigas in 8o° W in spring (October and November) agrees on 

 the whole very well with the results obtained by Ommanney (1936). His analyses of the 

 catches from i-m. nets, towed obliquely between the surface and about 250 m., showed 

 that in November, 1931, the greatest concentration of this species in 75 W lay im- 

 mediately to the south of the Antarctic convergence. In October, 1932, in about 8o° W, 

 he found the largest numbers at stations a little to the south and a little to the north of 

 the convergence. 



The distribution of the Chaetognath, Etikrohnia hamata (Table V and Fig. 6) is in 



