io6 



DISCOVERY REPORTS 



On the left of the figure, where Chaetoceros socialis is absent and Thallassiosira ant- 

 arctica less abundant, the average size of the krill is small, but on the right, representing 

 stations at the southern end of South Georgia, the average length is greatly increased, 

 and it is here that the two diatoms reach their maximum. It is open to question whether 

 the increase in size of the krill is a direct result of the greater abundance of these par- 

 ticular diatoms, or whether the correlation rests on a community of environmental con- 

 ditions, namely those to be found in the western Weddell Sea water affecting diatoms in 

 abundance and the euphausian in length. 



The results of Hart's examination of the stomach contents of adult and post-larval 

 Euphausia superba suggest that the correlation between abundance of Thallassiosira 

 antarctica and increased average length of the euphausians is a direct one: for he states 

 that on the occasions when this examination was made, of two forms which occurred 

 constantly, one was Th. antarctica. 



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®- 1926-27 CLASS 

 e -19 27-28 

 A-1928-29 

 0-19 29-30 

 H -1930-31 

 B -193 1 -32 



NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV 



Fig. 29. Half-monthly average length of Euphausia superba larvae obtained from 70-cm. vertical nets and 

 from the i-m. nets fished during the circumpolar cruise. 



AVERAGE LENGTH OF LARVAE 



In Fig. 29 there is represented the half-monthly average lengths of the Euphausia 

 superba larvae obtained from the 70-cm. vertical nets, except for the 193 1-2 series which 

 was taken in the i-m. nets fished during the circumpolar cruise. The scattered distribu- 

 tion of the average lengths gives some indication of the variation which can take place. 

 It is in part due, no doubt, to the different seasons involved and to local environmental 



