THE OLDER STAGES 185 



developmental state of the shelf eggs is distinctly in advance of the corresponding state in oceanic 

 water, and while this may merely mean that development on the shelf is more rapid than in the open 

 sea^ a slower sinking rate in the shallower conditions seems a distinct possibility. As compared with 

 the open sea, however, the shallow waters of shelf regions are relatively unstable, being subject to 

 considerable turbulence arising through vertical mixing, tidal movements and so on, and it may be 

 that this turbulence alone contributes to the near-surface occurrence of developmental stages that in 

 oceanic water are more commonly encountered at deeper levels. As Fig. 23 shows, wherever 

 advanced eggs containing developing nauplii were encountered in shelf water, they tended to occur 

 nearest the surface where the water was shallowest. 



OCEANIC WATER 

 -EAST WIND DRIFT >• < WEDDELL DRIFT- 



XL 



Fig. 23. Diagrammatic illustration of the developmental condition of the eggs in shelf and oceanic waters, the vertical egg 

 columns representing the actual condition recorded at every station where observations on egg development were made. 



It seems clear then that such eggs as we have recorded must in fact have been sinking and were laid 

 above 250 m. With the possible exception of those at Station 540 (Fig. 19), however, the numbers we 

 find at this near-surface level are so consistently small that one hesitates to suggest that it is there, 

 near the surface, whether in oceanic or shelf water, that spawning principally takes place. All in fact 

 that can safely be concluded from the meagre results of our analyses is that some sporadic surface or 

 near-surface spawning, evidently on a very minor scale, does take place in both shelf and oceanic 

 water, and that the eggs so laid do in fact sink, developing as they go down, to hatch at deeper 

 levels. 



Turning again to Fig. 19 and to such evidence as it may be said to provide as to what the depth 

 of spawning might be, it will be seen that while it does emphatically not appear to be the near-surface 

 phenomenon of Ruud there are two other distinct possibilities to be considered, (i) that the eggs 

 might be laid on or near the bottom in Antarctic shelf or slope^ water (Stations 540 and 2603), and 



1 This, however, seems unlikely. It is well known for instance from the work of Apstein (1909) and others that in many 

 fishes the eggs develop much more slowly in colder than in warmer water. 



2 Taking here the near-bottom occurrence of Second Nauplii at Station 2603 as indicating the presence, or very recent 

 presence, of eggs. 



