44 DISCOVERY REPORTS 



determined the food consisted of E. superba. Kemp and Nelson (193 1) report great quantities of this 

 species in the surface waters of the deep, now submarine, volcanic crater they discovered between 

 Cook and Thule Islands. In a long and important paper, to which many further references will be 

 made, Ruud (1932) in his report on the euphausians of 'Vikingen's' expedition to the Weddell Sea, 

 gives the first published account of the two-year life-cycle of the krill,^ a phenomenon then thought 

 to be without parallel among other euphausians, and gives the first short descriptions, with figures, 

 of the egg, First Nauplius, Metanauplius, First, Second and Third Calyptopis together with that of 

 an early Furcilia stage which is clearly the First. He emphasises that the species is essentially a surface 

 one, the Antarctic surface layer being the principal locus of abundance of both adults and larvae alike, 

 and calls repeated attention to the importance of the Weddell Sea current as a carrier and distributing 

 agent of the larvae in the Atlantic sector. From the monthly developmental condition of the ovaries 

 of the females he examined and from the brief period of larval abundance this expedition encountered, 

 he concluded that spawning was a ' spontaneous ', that is, not a protracted, phenomenon, which, during 

 the season ' Vikingen ' was in the field, was confined to the first half of January. He found a remarkable 

 scarcity of eggs and Nauplii in the plankton, a phenomenon leading him to suppose that the krill 

 spawn close to or right under the Antarctic pack, where, hidden away and beyond the reach of our 

 nets, the early larval development would take place. Rustad (1934) is the first to call attention to the 

 later (February) spawning characteristic (p. 177) of higher latitudes near the Antarctic mainland and 

 shows conclusively that in Thysanoessa macrura at least the early larval development takes place in 

 deep water and not at the surface as postulated by Ruud. Hart (1934), referring to the stomach 

 contents of adult and post-larval krill, states that the most frequently occurring remains are those of 

 the diatoms Fragilaria antarctica^ and Thalassiosira antarctica. In post-larval specimens he often found 

 entire examples of large Foraminifera (Globigerina sp.) and suggests they are possibly eaten for their 

 calcium content. Mackintosh (1934) refers to its extreme patchiness and tendency to form shoals in 

 the western Weddell drift region and notes that many of the big shoals have been seen at the surface 

 both by night and by day. Disregarding samples containing over 1000 specimens and so eliminating 

 what he has called ' the disturbing influence of heavy shoal catches ' he shows that Euphausia superba 

 undergoes only a minor degree of diurnal vertical migration and suggests that the greater part of the 

 population remains permanently near the surface, ' especially perhaps when forming shoals '. He calls 

 attention to how readily the older and more active krill dodge out of the way of a surface net by day 

 and shows that in the Falkland Dependencies this species is numerically among the most important 

 of macroplankton animals, including it in his ' cold-water ' group which in this region may occur in 

 large numbers anywhere south of the 3° isotherm. Hardy and Gunther (1935) describe its distribution 

 on the South Georgia whaling grounds and give the first eye-witness account in modern times of the 

 swarming habit there. Following Ruud (1932)^ they point out that it would seem likely that the older 

 larvae ('Furcilias' and 'Cyrtopias') encountered in this locality in March, April and May are not of 

 local origin but get carried there in the surface drift from some distant locus of spawning in the south. 

 They are the first to give a practical demonstration of the remarkable patchiness of its distribution. 

 From a wealth of material, Fraser (1936) gives the first comprehensive description, richly illustrated by 

 figures, of every stage of the larval development from the egg to the last Furcilia, and it is on this 

 classic account that more recent determinations of the eggs and larvae have been based. He discards 

 the former division of the later stages of euphausian development into Furcilias and Cyrtopias, and 

 this, together with his recognition that both are in fact Furcilias, of which in E. superba there are 



1 Already noted, however, by my former colleague, Dr J. F. G. Wheeler, in a report to the Discovery Committee in 1930. 

 ^ Revised by Hendey (1937) and now called Fragilariopsis antarctica. 

 ^ And incidentally it transpires (p. 43), Risting. 



