86 DISCOVERY REPORTS 



It will be seen then, that the temperature range of this species, while varying as might be expected 

 from month to month and from season to season, varies also, and varies quite significantly, from one 

 geographical region to another. It is neither a creature of the coldest Antarctic water nor of the 

 warmest, but essentially of both, its existence in one range of temperature or another depending 

 entirely upon the time of year and locality in which it may be found. 



Table 1 1 . Vertical net hauls. Monthly surface temperature range of the larvae in the West Wind 

 drift, Bransfield Strait and on the South Georgia whaling grounds (See heading to Table 4) 



Autumn 



A comprehensive view of the variation that may be encountered, in both time and place, is given 

 in Table 12, which, summarising the data in Tables 5-8, 10 and 11, shows the monthly temperature 

 ranges of the surface population in the four principal regions of its abundance, beginning the year in 

 each instance with January when (p. 102) the larvae first begin to appear in substantial numbers in 

 the surface waters of the Weddell stream. In this summary the figures for the optimum range are 

 based for the most part on average catch-figures of not less than 100 in the stramin nets and of not 

 less than 50 in the vertical nets. In instances, however, where no such catch-figures are available, 

 owing to the periodic scarcity of certain developmental phases in the plankton, the optimum range 

 is based on the two highest adjacent average catch-figures in the absolute temperature range. 



From these figures then, taking the optimum range as the most significant measure for regional 

 comparison, and considering in the first instance the surface population as a whole, it is evident that 

 E. superba could be described as a creature of the coldest Antarctic water — in the East Wind drift 

 from March to December, in the Weddell drift from July to December, in the Bransfield Strait from 

 April to November and on the South Georgia whaling grounds from at least August, but probably 

 before, to October. It could equally well be described as a creature that exists in from very cold to 

 moderately warm Antarctic water — in the East Wind drift from January to February and in the 

 Weddell drift from January to June — or as one that lives in from warm to moderately or very warm 

 water — in the Bransfield Strait from December to March and in South Georgian waters from about 

 the middle of November to the end of May at least, if not later. 



Taking now the three broadly grouped developmental phases in turn, and taking our data as before 

 from the optimum range, it will be seen that in the East Wind drift the larvae spend virtually their 

 entire surface existence in sub-zero temperatures, the few recorded in the low positive (o-oo° to 

 0-99° C) range in January being in fact the last Sixth Furcilias surviving (p. 371) from the previous 



