270 DISCOVERY REPORTS 



species involved. Bearing in mind the scattered and isolated distribution of most of 

 the earlier observations, this fact in itself provides striking evidence of the completely 

 circumpolar distribution of the more important species. 



More recent work in the Antarctic zone has been directed mainly at the elucidation 

 of the ecological problems presented by the phytoplankton. Hendey's valuable syste- 

 matic revision of the Bacillariophyceae is most conveniently considered here, however, 

 on account of its close relation to other observations based on Discovery material and 

 its recent date. 



From observations carried out on the Whale Factory ' Vikingen ' in the summer 

 season of 1929-30, Gran (1932, pp. 351, 352) concluded that the stabilization of the 

 surface layers was the most important factor favouring the onset of the main phyto- 

 plankton increase. It was extremely encouraging to find such close agreement with our 

 own observations from so distinguished an investigator (cf. Hart, 1934, p. 191)- On 

 this occasion Gran's observations were not sufficiently numerous to permit of much 

 further discussion in relation to the seasonal cycle. 



In considering the observations obtained during the Antarctic part of the Meteor's 

 programme, Hentschel has divided them into west Antarctic and east Antarctic sections. 

 The first of these coincides roughly with the area to which Norwegian whaling in- 

 vestigators give the same name, and which has also been called the Falkland sector. 

 The second refers to the region east of the Scotia arc to the longitude of Cape Town, 

 and south of 50° S lat. Summing up the conditions he observed in the west Antarctic, 

 Hentschel (1936, p. 229) points out that the absolute means for both microplankton 

 and Metazoa were the highest of all the regions investigated during the whole voyage. 

 He also comments on the richness of the region in Antarctic mammals and birds, 

 including large numbers of species dependent on land. Diatoms and Protozoa were the 

 dominant groups of microplankton, Coccosphaeriales falling entirely into the back- 

 ground. An inverse relationship between diatoms and Protozoa, in respect of their local 

 abundance and regional distribution, was observed. This is not readily apparent from our 

 more numerous observations obtained at all seasons of the year. It is, however, perhaps 

 significantly related to our observation of a very distinct inverse relationship in relative 

 {fiot absolute) abundance between these two groups at different seasons, Protozoa being 

 more important in the scanty winter microplankton. In all other respects Hentschel's 

 generalizations tally perfectly with our observations. 



In the 'east Antarctic', where the Meteor's observations were comparatively few, 

 Hentschel (1936, p. 301) points out its strong resemblance to his west Antarctic region, 

 though total plankton and diatoms were poorer, and the vertebrate fauna shows few 

 species dependent on land. Again the agreement with our findings is complete. 



The principal importance of the Meteor results in relation to the present work lies 

 in the evidence they provide concerning nanno-forms which may be missed by our 

 methods. Before embarking on a further consideration of this aspect, it is important 

 to realize that Hentschel has included some stations as Antarctic which we, with more 

 recent hydrological evidence, would regard as sub-Antarctic. He apparently took the 



