HORIZONTAL DISTRIBUTION, GROWTH AND DYNAMICS OF DISPERSAL 349 



(3) The gradual spreading, during the next 4 months, of the larvae to the east, until by April the 

 whole of the Weddell current, both above and below (Figs. 99 and loi), is carrying them in large 

 or enormous numbers. 



(4) The later, February and March, beginnings of the main larval outburst in the coastal or near 

 coastal waters of the East Wind zone (Figs. 98-101). 



(5) The seemingly abrupt ending of major eastward transport of larvae in the Weddell stream in 

 about 30° E (Figs. 93, 94, loi and 102). 



(6) The larval barrenness of a vast area of the circumpolar sea, namely, the West Wind drift, except 

 for certain circumscribed and widely scattered regions where it is affected (Figs. 93, loi and 102) 

 by cold water deflected from the East Wind zone. 



(7) The virtual absence of eggs and of any larvae whatsoever from an enormous area of the West 

 Wind drift in the Pacific sector (all nine charts). 



Gross distribution of total eggs and larvae 



Fig. 103 shows the gross distribution and relative abundance of the eggs and larvae where- 

 soever and whensoever they have been encountered in the circumpolar sea. It uses the vertical net 

 hauls of every southern voyage we have made since 1927,^ the massed observations of these many 

 cruises emphasising again the overriding importance of the Weddell stream as a carrier of the larval 

 krill, throwing into sharp relief the general barrenness of the West Wind drift, a barrenness extending 

 up to particularly high latitudes in the Pacific sector, and demonstrating that all but a relatively 

 insignificant part of the immense total larval population must pass the winter beneath the polar pack. 



Growth and dispersal in the surface drift 



The northern or Weddell zone. From the dates of the earliest substantial risings in Weddell West and 

 the dates of the earliest major occurrences of the Sixth Furcilia in Weddell East, the only sector of 

 the current in which we have observations covering every month of the year, some estimate can be 

 formed of the time the young surface swarms take to complete their larval development.^ The 

 first substantial rising recorded in Weddell West took place (p. 314, Fig. 77, Station N 42) on 

 18 January, the first Weddell East swarms with the last larval stage clearly dominant (p. 339, 

 Fig. 95, Stations 2365 and 2372) being recorded on 13 and 16 July. This suggests that the purely 

 larval developmental phase in the surface takes about 6 months to complete. There is, however, 

 some uncertainty in this estimate. First, it is difficult to reconcile such a long period with 

 the early appearance of the penultimate (Fifth Furcilia) stage which as we have seen (p. 331, 

 Fig. 90) may be encountered already dominant in the surface swarms in the second half of March, 

 only 60-70 days after the earliest Calyptopis risings. Second it is based on an assumption that can 

 only partly be upheld, the assumption that the populating of the far eastern reaches of the Weddell 

 stream is brought about exclusively through the eastward spreading in the surface drift of larvae that 

 spring from risings in Weddell West. 



Taking these objections in turn, it is obvious that if we are to accept unreservedly such a long period 

 as normal for the surface life-cycle of the larva it must be assumed that once it reaches its penultimate 

 phase there must ensue a long and scarcely credible period, lasting several months, during which it 

 remains dormant as the Fifth Furcilia. That some such period of dormancy or retarded growth might, 



^ Augmented (p. 289) by those of the Norwegian and Australasian expeditions between 1927 and 193 1. 



^ The earliest appearance of the Sixth Furcilia is in the second part of March (p. 331, Fig. 90) when very small 

 numbers are recorded in the plankton of Weddell West. We are concerned here, however, with the major aspects of the larval 

 development, in other words with the time when the Sixth Furcilia first appears as the dominant stage in the larval, or mixed 

 larval and adolescent, swarms. 



