312 DISCOVERY REPORTS 



From the dates of the major January recordings of these surface forms some estimate can be formed 

 of the duration of the developmental ascent. All, both Norwegian and British, fall late in the month, 

 from the 22nd onwards, and since the earliest recorded major spawning in Weddell West is in 

 December (at Station 540 on the 19th) and since there is no evidence of any large-scale populating of 

 the surface layers there throughout that month, it would appear probable that the bulk of the developing 

 eggs and ascending larvae spend at least 30 days in their deep environment before the latter, as First 

 Calyptopes, reach the surface on any substantial scale. What part of this time is spent in the actual 

 ascent is harder to judge for we do not know how long the eggs, after being shed, take to develop to 

 the point of hatching.^ We do know, however, that hatching must be taking place deep down through- I 

 out December (p. 300) and on that ground it might be supposed the developmental ascent takes the 

 better part of a month, if not longer. J 



From the East Wind zone we have a single mid- February observation off the Princess Martha Coast " 

 to suggest that at its earliest the arrival of the First Calyptopes at the surface there takes place about 

 a month later than it does in Weddell West. The preponderance, however, of negative, or virtually 

 negative, observations in the former region, especially between 30° W and 60° E, suggests that it ■ 

 may not in fact be until March (p. 311, Fig. 75) that the accomplishment of the developmental 

 ascent becomes general in these high latitudes. 



There is one anomalous occurrence of three Calyptopes, two First and one Second, which lies 

 actually outside the Antarctic convergence immediately to the west of the S-shaped bend in it that 

 occurs about half-way between the Falkland Islands and South Georgia. No doubt this anomaly can 

 be ascribed as already recorded (p. 76) to the complex and somewhat unstable hydrological conditions 

 that seem to exist in this locality. 



March-April. In general the March-April distribution of the surface Calyptopes (Fig. 75) 

 follows closely that of the deep larvae for the same period. The whole of the Weddell drift from west 

 to east is now carrying large, sometimes enormous, numbers, and in the East Wind drift, notably 

 again in the Australian-Indian Ocean- Atlantic sectors, it is evident that, although our observations 

 there are rather few and widely scattered, there is an almost equally substantial surface population 

 in the slope, coastal or near-coastal waters from March onwards. 



Turning again to Figs. 74 and 75 it will be seen that as with the deep larvae there is again a 

 west to east shift involving by March the extension of the principal concentrations of the surface 

 Calyptopes, confined in January-February to Weddell West, to a point about half-way along Weddell ' 

 Middle, an extension that at first sight seems to be simply the result of the easterly movement of the 

 surface stream. While the surface drift is manifestly involved it is not, however, the sole instrument of 

 easterly dispersal, comparison of the developmental condition of the surface swarms in Weddell West 

 in February with the corresponding condition of those of Weddell Middle in March, and further j 

 comparison of the developmental condition of the Weddell Middle March swarms with the cor- 

 responding condition of those encountered still farther east in April, suggesting very strongly that an 

 equally important transporting agent is the cold bottom current out of which the new-born krill seem | 

 to be rising. This is illustrated graphically in Fig. 76 which shows the stage frequency of the total j 

 surface larval catch at eighteen stations covering the Weddell drift from west to east, Weddell West in 

 February, Weddell Middle in March and Weddell East in April. The stations are arranged in the 

 order of their progression towards the east, that is, in the direction of flow of the surface stream, the j 

 gatherings of the several stages obtained at each station being expressed in each instance as a per- 

 centage of the total catch in the surface (250-0 m.) layer. The number (not the percentage) of deep 



1 In the eggs of Meganyctiphanes norvegica, Heegaard (1948) gets the impression that the period, spawning to hatching, , 

 might last for 5 or 6 days. 



