DISTRIBUTION OF ANTARCTIC MACROPLANKTON 149 



Whereas other lines crossing the northern zone have at their southern or south- 

 eastern ends an area of scarce plankton, most of these have at their south-eastern ends 

 the rich plankton of the neighbourhood of South Georgia. The first line, however, 

 (WS 140-2) is an exception, for in February 1927-8 the plankton was unusually thin 

 around the north and west sides of South Georgia, and between WS 141 and WS 142 

 we find the familiar abrupt change from a rich to a poor plankton. It must be admitted 

 that at these three stations the plankton is patchy. Rhincalanus is the dominant 

 copepod at WS 141 and WS 142, but at WS 140 this species is far exceeded by the 

 young stages of Calanus propinquus. At WS 141 the net evidently passed through a shoal 

 of Limacina. Apart from these species, however, the differences between the three 

 stations lie in the quantity rather than in the constitution of the plankton. 



The next line (WS 254-6) was the only winter line across the northern zone, and is 

 therefore hardly comparable with the others. The plankton of course was very thin, 

 but had moderate numbers of Euphausians towards South Georgia. The plankton at 

 WS 254, a midday station, was practically negligible. 



At WS 314-16 there is again a rather sharp fall in the quantity of plankton from 

 WS 315 to WS 314. At all three stations however Rhincalanus dominates the whole 

 sample except for the exceptional catch of Parathemisto at WS 315. Other species are very 

 uniform, though there is a slightly disproportionate number of Thysanoessa at WS 315. 



At WS 413-16 the Chaetognatha increase steadily towards the convergence and 

 Calanus acutus towards South Georgia. Parathemisto is fairly steady, but Rhincalanus 

 is the most plentiful copepod only at WS 414. At WS 415 it is equalled, and at WS 416 

 it is exceeded by Calanus acutus. Euphausians are inclined to be irregular. 



In the line WS 427-30 Rhincalanus is the principal copepod at all four stations. 

 Limacina increases towards the convergence, and the Chaetognatha tend to do the same, 

 though they fall off at WS 430. Calanus propinquus and Thysanoessa are quite evenly 

 distributed, though the former increases a little towards South Georgia. 



WS 465 is quite typical of the northern zone with its abundant Rhincalanus and 

 Chaetognatha, but WS 466, which is almost on the convergence, has unexpectedly large 

 numbers of Calanus acutus and C. simillimus. 



In the line WS 521-6 there are more stations between the convergence and South 

 Georgia than in any other. The quantity of plankton varies considerably, but this is 

 largely due to the diurnal variations of Thysanoessa. At WS 522 and WS 525 the samples 

 were taken near the middle of the night and at the other stations near the middle of the 

 day, and at the former Thysatioessa was enormously abundant and at the latter relatively 

 scarce. At WS 521-4 Rhincalanus was much the most abundant copepod, but at WS 525 

 and WS 526 (nearer to South Georgia) it was replaced by Calanus acutus and C. pro- 

 pinquus. C. simillimus was evenly distributed except at WS 525, and Parathemisto except 

 at WS 522. There was the usual increase of Chaetognatha towards the convergence and 

 a shoal of Limacina at WS 521. 



The last line (Sts. 656-9) differs from nearly all other lines across the northern zone 

 in the small amount of plankton taken at each station. Parathemisto and Thysanoessa 



