324 DISCOVERY REPORTS 



of December), stage iv is almost absent, stage v is dominant and adults are present in 

 large numbers. In some of the hauls from these stations north of the convergence adults 

 (stage vi) are even dominant. At stations south of the convergence (Sts. 731, 733, 739, 

 741 and 745), stage iv is usually present in fairly large numbers, especially in the lower 

 hauls, but stages younger than this are absent. At Sts. 735 and 737, the most southerly 

 of the stations in the Drake Passage, fair numbers of stage iii were taken (at St. 735 more 

 than 20 per cent in the lower net). Thus the stock north of the convergence is definitely 

 older than the stock south of it, and the stock in the warmer Antarctic water is apparently 

 older than that in the coldest Antarctic water. Now the stock found at these stations at 

 the western end of the Drake Passage in November 193 1 was in the course of or had just 

 completed its spring ascent to the surface. It had just passed the winter at a depth 

 below 250 m. Further, several considerations lead one to believe that the young stages 

 (stage iii) found at the edge of the ice do not result from a recent spawning. In the first 

 place they are not present in sufficient quantities to indicate a recent spawning. At St. 

 735 only 22-0 per cent stage iv and 11-7 per cent stage iii were found in the two hauls 

 together, and at St. 737 only 26-0 and 9-7 per cent of stages iv and iii respectively. 

 Stage ii was present at each station in very small numbers, and no stage i or nauplii were 

 found. In the second place, we have seen from figures for the following season that the 

 adult females at this time of year are not yet ripe and no males had appeared. It seems 

 evident, then, that in the coldest Antarctic water, with an average temperature less than 

 — 1-5° C, the stock in the spring, which had just passed the winter below 250 m., con- 

 tained a proportion of individuals which had not developed beyond stage iii. The stock 

 in the warmer Antarctic water (average temperature below about 3-0° C.) appears to 

 have developed as far as stages iv and v by the spring and that in water north of the 

 convergence as far as stages v and vi. The population in all these three classes of 

 water probably results from a mid-winter spawning, as we shall see later (p. 338), 

 and it must be assumed either that the stock in Antarctic water with an average 

 temperature less than — 1-5 °C. has been spawned later in the winter than that in 

 warmer Antarctic water (average temperature below about 3-0° C), or else that it was 

 spawned at the same time as the stock farther north but that its rate of development 

 has been retarded. Similarly the stock in the warmer Antarctic water must either have 

 been spawned later than the stock north of the convergence or else have developed 

 more slowly during the winter months. 



In the main the stock curves of the population in the western Drake Passage in 

 November 1931 show that the species rises to the surface from its winter level prin- 

 cipally in stages iv and v, so that one may say that Rhincalanus gigas, like other species 

 of oceanic Copepoda (S0mme, 1934, Calaniis finmarchicus and C. hyperboreus; NichoUs, 

 1933, C finmarchicus; Campbell, 1934, C tonsus and Euchaeta japonica; and others) 

 spends the winter months in these two stages. 



At the stations in the eastern Drake Passage and in the South Atlantic near the 

 Falklands at the end of November stages iv and v were predominant and the pro- 

 portion of adults was high in the lower nets. 



