NOTES ON THE SPECIES 261 



closely with Cleve's description (1894-5, Pt. i, p. 1 19 ; Pt. 2, pi. i, figs. 3, 4) of this species 

 were frequently observed upon whales, but not in samples of littoral diatoms at South 

 Georgia. It is, however, almost certain to occur there as a bottom form. The endo- 

 chrome of the individuals found upon whales was of a markedly brownish tint. 



NOTE ON BALEEN DIATOMS 



A few scrapings from the baleen of all three species of southern rorquals were ex- 

 amined while working on the skin-film diatoms at South Georgia in 1 930-1. Among 

 the film of the protozoan Haematophagiis, commonly found on the baleen, remains of 

 pelagic diatoms were numerous, but three characteristic species, one of Cymbella and 

 two of Noriciila, constantly occurred undamaged in large numbers, and it would appear 

 from their colourless cell contents that this may indeed prove to be their normal 

 habitat. 



AN OUTLINE OF EXISTING KNOWLEDGE OF WHALE 

 MOVEMENTS AT SOUTH GEORGIA 



A brief summary of the present state of our knowledge concerning whale movements 

 on the South Georgia grounds is necessary in order to appreciate the possible value of 

 the diatom data. Most of the published work is concerned with Blue and Fin whales, 

 which have furnished the bulk of the catch on these grounds ever since the intensive 

 fishing of Humpbacks ceased. Sei whale, however, provide a most important link in 

 the chain of evidence when the diatom data come to be considered, so that a brief state- 

 ment of the evidence concerning their migrations may be given before proceeding to the 

 main topic. 



Unlike the larger southern rorquals, southern Sei whales appear to pass the greater 

 part of their time in sub-Antarctic and sub-Tropical waters, making a brief journey 

 south late in the season, when the water temperature is at or past its maximum. They 

 very rarely appear on the South Georgia grounds before February and are generally 

 most numerous in March, after which their numbers fall away again even more rapidly 

 (Harmer, 1931, p. 106). This difference in behaviour is probably bound up with 

 differences in feeding habits. While Blue and Fin whales appear to feed very little when 

 in warm or temperate seas, being almost entirely dependent upon the dense shoals of 

 Euphaiisia superba encountered on their southern migration, Sei whales are known to 

 feed extensively on the dense shoals of " lobster-krill " (pelagic post-larval Miinida 

 gregaria) so common at times off the Patagonian coast (Matthews, 1932, p. 483). 



Our knowledge of the movements of the more important Blue and Fin whales may be 

 gathered from three main sources: Mackintosh and Wheeler (1929), in which the work 

 of earlier writers is summarized, Harmer (1931), and Kemp and Bennett (1932). 



All authorities seem well agreed that there is in both hemispheres an annual migra- 

 tion polewards in summer for purposes of feeding and to warmer waters in winter for 

 purposes of breeding. When we come to consider the catches on any given whaling 

 ground, such as that off South Georgia, it at once becomes apparent that the course and 



