2o6 DISCOVERY REPORTS 



to Antarctic hydrology that could be held responsible for such a phenomenon — the sinking of the cold 

 highly saline shelf water which as Deacon (p. 99) has shown is formed in winter, on a major scale 

 in the south-western part of the Weddell Sea and on a lesser scale between the South Orkney and the 

 South Shetland Islands, and the subsequent spreading of this water northwards and eastwards below 

 the Weddell drift as the Antarctic bottom current. This, for the time being at any rate, hypo- 

 thetical conception of transport from shelf to deep water is illustrated diagrammatically in Fig. 3 1 , 

 which as before shows a shelf sea with deep oceanic water beyond, the sinking from the shelf of the 

 cold water supposedly carrying eggs, the hatching in deep water and the subsequent developmental 

 ascent. It is true that this mechanism cannot easily account for the frequency of eggs and scarcity of 

 early larvae we record in the Bransfield Strait, sometimes 100-200 miles away from the oceanic 

 depths outside. There is something yet to be explained here,^ but it is a mechanism which may well 

 apply to eggs laid on parts of the Weddell shelf and slope which are near enough for transport into 

 oceanic depths before they hatch. The eggs for instance recorded near 55° W beyond the eastern end 

 of the Bransfield channel (p. 298, Fig. 68) are not in fact very far away from the deep sea. 



Speculative although this hypothesis may seem it is nevertheless not entirely without substance, 

 for at least we have reason to believe (p. 100) that the cold bottom water flowing eastwards under the 

 Weddell Sea is carrying eggs, and doubtless First and Second Nauplii as well, and carrying them it 

 seems (p. 213) with considerable velocity. It seems, too, to have some measure of claim to be a 

 working hypothesis, providing as it does a not unduly far-fetched explanation, in so far at least as one 

 can search in Antarctic hydrology for one, of our otherwise inexplicable failure to find substantial 

 evidence of hatching in the shelf waters in which, or close to which, it seems so much of the spawning 

 takes place. Whatever substance however it may eventually prove to have one thing seems certain. 

 In view of the lack of evidence of mass sinkings of eggs (p. 185) to hatch at deeper levels and of our 

 failure so far to find the spent and gravid females at the great depths where clearly the eggs are hatched, 

 only intensive exploration of the cold bottom water below the Weddell and East Wind zones and the 

 subsequent discovery, not once or twice, but consistently and over a wide area, of substantial numbers 

 of spawning females there, will prove it to be substantially wrong. In the meantime, it may be observed, 

 the distant off-shore occurrences of deep recently hatched larvae recorded below the Weddell drift 

 and the coastal or near-coastal occurrences of the deep stages recorded below the East Wind drift 

 (p. 200, Fig. 28) are not inconsistent with the part I have supposed the bottom water to play in the 

 dispersal of the eggs and naupliar stages. For as Deacon in the passages already quoted has 

 shown (pp. 99-100) the cold water does not sink everywhere from the shelf to flow away as a major 

 current — it does so only in the Weddell Sea, the higher salinity and temperature of the warm deep 

 water elsewhere forming all round Antarctica an effective barrier to such a movement. If, however, 

 the shelf water, supposedly carrying eggs, were in fact sinking all round the Antarctic continent and 

 flowing away to the north we should expect to find, not as we do find in the Weddell region only, 

 but all round Antarctica, deep concentrations of Nauplii and Metanauplii much farther away from 

 the land than our observations have shown them to be. The inshore or near-coastal distribution of the 

 deep larvae in the East Wind zone, therefore, is only it seems what might be expected if the conception 

 of transport from shelf to deep water is correct and the sinking Weddell shelf water the instrument 

 engendering the eastward dispersal of the shelf and slope laid Weddell eggs I suspect it to be. 



By whatever chain of events the eggs and Nauplii come to be in the bottom water, deep transport 

 to the east of course implies that both must spend some considerable time there if they are to be 

 carried any distance along. There are some grounds for supposing they do. Heegaard (1948), for 

 instance, finds that in Meganyctiphanes norvegica the period, spawning to hatching, might last for 



^ It may be (see p. 121) that the hydrostatic pressure at the bottom of the shelf seas is too low for successful hatching. 



