,8^ DISCOVERY REPORTS 



the deepest net. Our failure to make a systematic exploration of this near-bottom stratum may in fact 

 have been vital and it might have been more profitable it seems if we had taken greater risks, for it must 

 surely be significant that the net which probably came within closer striking distance of the sea bed 

 than any other of the shelf series, the 500-250 m. net at Station 540, should yield the second largest 

 catch of eggs we have so far recorded. Failure to make systematic search in the near-bottom stratum 

 of the slope waters of the continental land must also it seems be held to account for our failure there to 

 strike them, the vertical distribution at Station 2603 (Fig. 19 and p. 93, Table 14) of that very near 

 product of hatching, the Second Nauplius, distinctly suggesting that had we gone still deeper^ on 

 that occasion we might well have struck them, lying possibly on the bottom itself. Finally, turning to 

 the open sea (Fig. 19), it seems obvious, having regard to the apparent vertical distribution at 

 Station 2594, that our failure (except once) to sample them in mass over deep water must simply be 

 ascribed to our failure to carry out systematic observations (p. 98) at great depths below 1000 m. 



We may turn now to the possibility, originally suggested by Fraser, that although shed at higher 

 levels they may sink before hatching to depths below 1000 m. In 3608 of the 

 4231 eggs identified by Fry and me from the vertical samples the state of develop- 

 ment was clearly distinguishable, some being unsegmented or just beginning to 

 divide, others fully segmented with relatively large or with very small cells, the 

 most advanced showing varying degrees of naupliar development culminating in 

 the easily recognisable form of the First Nauplius evidently near the point of 

 hatching. A diagrammatic illustration of the developmental condition of those 

 taken between the surface and 1000 m., based on the numerical record given 

 in Fig. 20, is shown in Fig. 21 in which the conditions in shelf and oceanic 

 water are compared. Taking the picture as a whole it will be seen that the eggs 

 approach progressively nearer to a ripe condition as the depth increases, and the 

 inference seems to be that those recorded in both shelf and oceanic water were in 

 fact sinking eggs that were developing towards maturity as they went down. It 

 would appear too, that they were Uberated in their unsegmented state, as Fraser 

 (1936, p. 17) found with his laboratory-spawned specimens, that they were liberated in the Antarctic 

 surface layer and that by the time they had sunk below 750 m. the majority had developed incipient 

 or clearly recognisable naupliar forms. 



Of the total of 3444 eggs recorded at oceanic Station 2594 the developmental condition was 

 recognisable in 2880 and is shown separately in Fig. 22. It will be recalled (p. 100, note 2) that the 

 deep 1 500-1000 m. net at this station unfortunately failed to close, fishing from 1500 m. open to the 

 surface. We cannot, therefore, be certain of the level, or levels, at which this exceptionally large 

 catch was made. It might be supposed however from (i), the absence of eggs from all levels above 

 1000 m., from (2), the high proportion of the total catch, 75%, that contained developing nauplii, 

 and from (3), the developmental condition of the deep eggs in oceanic water generally (Fig. 21), 

 that an unknown but probably very considerable portion of it did in fact come from the 

 1 500-1000 m. horizon to which it is possible it may have sunk from a higher level.^ 



Recent laboratory experiments by Marshall and Orr (1953 «) indicate that the eggs of Calanus 

 finmarchicus tend to sink more slowly in water at 0° C than they do in warmer water. It seems too 

 that under natural conditions the eggs of E. superba behave in the same way, sinking more slowly 

 in the colder waters of the shelf than they do in the warmer conditions of the open sea. It will be 

 seen (Figs. 20, 21 and 23) that at all subsurface levels where significant numbers are involved, the 



1 The deep 1400-1000 m. net at this station came within approximately 50 m. of the bottom in 1450 m. 

 - See, however, p. 210. 



Fig. 22. Developmental 

 condition of the eggs at 

 St. 2594. 



