THE OLDER STAGES 205 



been recorded in the shallow water of the Antarctic continental shelf. In the first place it will be seen 

 (p. 201, Fig. 29) it is there, and there only, that the rarely seen First Nauplius has ever been en- 

 countered, and secondly that all three stages, the First Nauplius, the Second Nauplius and the 

 Metanauplius, in their vertical range consistently approach far closer to the surface than their counter- 

 parts in deep water, the Second Nauplius and the Metanauplius, are ever found to do. Obviously, 

 as already stated (p. 98), the absence of the First Nauplius from our oceanic stations is simply 

 because there it occurs beyond the range of our deepest nets. It seems equally obvious that its rare 

 occurrence in shallow water is simply because the few eggs that hatch there, and hatch it would 

 seem on the bottom, must sometimes, in shallow soundings, inevitably be so near the surface on 

 hatching that the First Nauplius cannot fail to come within striking distance of it almost immediately 

 it begins to climb. Bottom hatching in shallow water must also of course explain the occasional near- 

 surface occurrence in shelf seas of the Second Nauplius and the Metanauplius. 



A more realistic illustration of the near-surface occurrence of the Nauplii and Metanauplii that 

 results from the occasional hatching that takes place in shallow water, as compared with the deep-sited 

 occurrence of these stages that results from hatching in the open sea, is given in Fig. 30, which, again 

 representing a shelf sea with deep oceanic water beyond, shows what evidently must happen to eggs 

 which, supposedly laid not far below the surface in both shelf and oceanic water, subsequently sink, 

 developing towards maturity as they go down. 



Fig. 30 is based somewhat broadly on Fig. 20 and it will be seen that I have not used a true vertical 

 scale, nor have I pictured the developmental phases of the eggs quite as they would appear if based 

 exactly as shown in the earlier diagram. However, the main purpose of this figure is to emphasise 

 again (i) that such eggs as we have recorded are evidently sinking, (2) that they develop progressively 

 nearer to maturity as they go down, and (3) that in shallow water those that complete the final 

 stages of their development and eventually hatch, it seems on the bottom, cannot help giving rise to 

 Nauplii and Metanauplii much closer to the surface than the Nauplii and Metanauplii in the deep 

 ocean could ever be expected, and are ever in fact found, to be. In fact, since the trend in Fig. 20 

 shows the penultimate egg stage at depths round about 500-750 m. we must assume that the eggs in 

 the final stage (with fully developed nauplius) must sink from somewhere near 1000 m. to about twice 

 this depth before they hatch. 



Influence of the sinking shelf water on the liberated eggs 



Unless some major blunder has been made in the interpretation of the data — as, for example (i) too 

 much having been assumed from the frequency of occurrence of eggs in shallow water, (2) too much 

 from the solitary discovery in a shelf sea of any concentration of eggs at all, (3) too much from our 

 failure to find, except in the surface layers, spent or gravid females in the concentration in which we 

 should expect them to be if spawning were to take place at great depths, and (4) too much from our 

 failure to find evidence of large-scale hatching other than deep down in the open sea, then it seems 

 clear enough that, although the shelf and possibly slope waters of the far western and south-western 

 reaches of the Weddell drift are apparently a major locus of the spawning krill, the bulk of the eggs 

 deposited there, instead of hatching and producing large numbers of Nauplii and Metanauplii in 

 situ, do so on the contrary in the open sea at great depths and at varying distances from the shelf. 

 If, as Fraser (p. 179) originally suggested, the eggs when laid do in fact normally sink below 1000 m. 

 before hatching it would follow that those that are laid in shelf water, as they continue to sink, must 

 inevitably come in contact with the bottom itself, there presumably to lie until they hatch. Since, how- 

 ever, such as do hatch there are so rare it seems possible that all but a very few do not remain in the places 

 where they fall but get carried away to hatch at deeper levels. There is only one movement known 



