368 DISCOVERY REPORTS 



(2) Whether among purely larval, or mixed larval and adolescent swarms, the Sixth Furcilia remains 

 dominant almost to the end of w^inter, but in September is rapidly surrendering and occasionally 

 losing its dominance to the early adolescent. 



(3) Exceptionally it seems the Fifth Furcilia may remain dominant until late August, a pheno- 

 menon to which reference has already been made on pp. 349-51. 



(4) Fraser's conclusion (1936, p. loi) that 'the vast majority of the larvae reach the Furcilia 6 

 stage before the end of the southern winter', while correct as far as his material went, can now only 

 be considered valid for the northerly region of larval abundance in the Weddell drift and on the South 

 Georgia whaling grounds. In their high latitude region of abundance in the East Wind zone, from 

 which Eraser had no material, clearly, it has now been established, they grow so slowly that vast 

 numbers of them not yet in the Sixth FurciUa stage must persist at least throughout September and 

 possibly (pp. 334-8) until long after. 



(5) Both larval and mixed larval and adolescent swarms display a heterogeneous pattern of modal 

 values throughout the season. 



Spring. The distribution and relative abundance of the massed surface larvae in spring (October- 

 December) is shown in Fig. 117. Except for a single instance in Weddell East (Fig. 118, Station 

 2447) where a few Fourth and Fifth Furcilias were recorded still surviving in early October, the 

 surface larvae, everywhere throughout the ice-free zone, have reached the Sixth Furcilia stage and 

 in this state survive until November by the end of which, in the Weddell drift at least,^ all have become 

 adolescent. During this, the final phase of their existence in the plankton, they continue to be massed 

 in considerable abundance throughout the greater part of the Weddell zone, although nowhere, except] 

 for three instances on the heavily sampled South Georgia whaling grounds, in such enormous numbers 

 as are encountered in winter. There is, however, a curious, largely barren, area in Weddell West, and 

 two alternative explanations are suggested to account for it. Either (i) our nets through chance missed 

 the larger mixed larval and adolescent swarms or, (2) and perhaps the more likely, the region is one 

 from which by springtime the young purely larval swarms encountered earlier in the year have already 

 passed onwards in the surface stream to the South Georgia whaling grounds and beyond. The isolated 

 minor occurrence of the Sixth Furcilia that appears about half-way along this section of the drift, 

 the plot representing the larval component of a young mixed larval and adolescent swarm (Fig. 118, 

 Station 1868) recorded there in November, need not necessarily, therefore, have been of local 

 origin. It could probably in fact be traced to a rising that originally took place in the East Wind drift, 

 possibly, as suggested on p. 357, off the Princess Martha Coast. Similarly, the November swarm with 

 a dominant larval component encountered in the Bransfield Strait (Fig. 118, Station WS 488) 

 could, in view of its backward developmental state and position at the extreme western end of the 

 channel, also have got carried there from the East Wind drift, being probably traceable to the north- 

 ward deflection of East Wind water that occurs near Peter I Island. 



Between 30° and 60° E, it is evident that there has now been some minor overflow of young spring 

 swarms from the richly populated Weddell drift. Elsewhere the West Wind drift is largely barren 

 of larval stages except again south-east of Kerguelen where there is a conspicuous instance of larval 

 encroachment from the East Wind zone, the major occurrence of the Sixth Furcilia recorded there 

 (Fig. 118, Station 1640), an early December record, suggesting that in isolated regions such as 

 this the young first year swarms diverted from the East Wind zone, although developing considerably 

 more rapidly (p. 327) than their contemporaries in higher latitudes, grow less quickly than, and in 

 consequence do not, in general, become exclusively adolescent until later than, the swarms that are 

 carried in the Weddell stream. All our observations in the West Wind region south-east of Kerguelen 



1 See again, however, p. 338, note i. 



