346 ■ DISCOVERY REPORTS 



upwards from beneath the Antarctic surface layer. One may therefore expect that the 

 stock of Rhincalanus taken in the lower nets at this station has been carried into this 

 position in warm deep water from somewhere farther north. The stock at this station 

 (i 1 15) is, therefore, probably much the same as that at St. 1 1 16, and it may be possible to 

 explain the comparatively high percentage of adults at St. 11 15 on the assumption that 

 the autumn descent from the surface has already begun in this area (as it apparently 

 has — see Fig. 12), and that, if adults sink into the warm deep water before the 

 younger stages, as we have elsewhere supposed that they do (p. 340), a high proportion 

 of adults may be expected in this water where it is found moving upwards as at St. 1 1 1 5. 

 At Sts. 1 1 16 and 1 1 17 we see what is evidently the summer generation in an advanced 

 state of development. At St. 11 16 the population consisted of stages iv and v, with a 

 small proportion of adults, and at St. 11 17, farther north near the convergence, the 

 population is considerably older and consisted of stages v and vi (adults). The spawning 

 therefore which gave rise to the stock at St. 11 17, in the warmer waters of the Drake 

 Passage, must have taken place earlier in the year than that which gave rise to the stock 

 at St. 1 1 16, in the colder water. No deep hydrological observations were made at St. 

 1 1 16, so that it is not possible to say with certainty whether it lies within the optimum 

 range (an average of i ■0-4-0° C. for the o-ioo-m. layer) of spawning or outside it. The 

 surface temperature was 2-76° C, so that it seems probable that this station lay 

 within these limits. It must be remembered, however, that the population sampled 

 at this station in early February had drifted from considerably colder water farther to 

 the south-west where the average temperature (Fig. 7) may have been lower than i-o° C. 

 At St. 1 1 17 the average temperature was 4-11° C, but the population sampled at this 

 station must again have drifted from the south-west where the temperature of the water 

 was colder than this, though probably not colder than i-o° C. (Fig. 7). The age of the 

 stock at both these stations seems to point to an early spawning in these waters. In the 

 season 193 1-2 it was seen that spawning took place first in December east of South 

 Georgia and later in the Scotia Sea and Drake Passage. In the season 1932-3 it has been 

 suggested, from the time of appearance of a high proportion of males and of the attain- 

 ment of maturity by the over-wintered generation, that spawning may have taken place 

 earlier than in the previous season. The condition of the population at Sts. 11 16 and 

 1 1 17 in the Drake Passage in early February 1933 seems to confirm this suggestion, 

 although it is evident from the stock curves at St. 1083 (stages v and vi ; Fig. 27), south 

 of South Georgia, that no spawning took place in the colder waters of the Scotia Sea 

 before the end of December. As will be seen in the following section (p. 348) conditions 

 at Sts. 1 1 27 and 1131 also point to a later spawning in the Scotia Sea, as compared 

 with the warmer waters farther west near the convergence. 



Falkland Islands to South Georgia, February 1933 (Fig. 28, Table VI //) 



The Rhincalanus population was analysed at five of the stations taken between the 

 Falkland Islands and South Georgia in late February 1933. 



On the Antarctic side of the convergence stages iii and iv predominated at the two 



