98 DISCOVERY REPORTS 



captured. Other examples of deep Metanaupliar moulting are provided by the analyses for Stations 

 823, 1138, 1144 (Table 13) and 1545 (Table 14), while the unmistakable growth of this stage during 

 its upward passage at Station 647 (Table 13) is revealed by the length frequencies given by Fraser 

 (1936) which are shown below. 



Table 16. Growth of the ascending Metanaupliiis as revealed by the length frequencies at Station 64^} 

 {after Fraser), the frequencies in Roman type, the range of size {in mm.) in italics 



Depth 0-84 0-87 o-8g o-go o-g2 o-g4 o-gs o-gj o-g8 i-oo V02 1-03 1-05 Average 



(m.) length 



750-500 ___ 4 2 10 22 41 5 7 3 4 2 0-97 



1000-750 2 5 16 21 25 17 7 52 — — — — o-g2 



So far we have traced the development of the early larva from the Second Nauplius to the First 

 Calyptopis stage and seen that during this phase in oceanic water it rises from great depths to the 

 surface. All now that is required to complete the early developmental history is to fit into its probable 

 position in the bathymetric scale the rarely seen First Nauplius, a stage so far not yet encountered in 

 oceanic water, even in our deepest nets. It seems a matter for simple deduction, however, to conclude 

 that the main mass of it, superimposed upon that of the hatching eggs, must lie well below the 

 1500 m. level, and that our failure so far to sample it is simply because in the vast majority of instances 

 our nets are not going deep enough. 



The actual bathymetric range of the newly-hatched larva is still of course a matter for conjecture, 

 but it is not difficult to see that as it climbs it must moult and become a Second Nauplius long before 

 it can reach the 1500 m. level, otherwise at least straggling specimens of it would surely have been 

 found by now in the 1 500-1 000 m. layer. The stage undoubtedly exists, for unmistakable specimens 

 of it, swimming freely about, have been found, although so far only in negligible numbers, all, 

 paradoxically,^ from shallow, or from near shallow, water. Only thirteen specimens have been identi- 

 fied with certainty, eleven by Fraser and me from the shelf water of the Bransfield Strait and Ross Sea, 

 and two by Ruud, both from the deeper (450-200 m.) net hauls made at ' Vikingen ' Stations 1 1 and 12, 

 close to the ridge of the Scotia Arc in the western part of the Weddell Sea. The scarcity of First and 

 Second Nauplii in his samples led Fraser to suggest that both stages may have a very fleeting existence, 

 while Ruud attributed his scarcity to the hypothesis that they, along with the hatching eggs, would 

 normally be found in the as yet inadequately explored water close to or right under the drifting ice. 

 As Rustad (1934) points out, however, although the movement of pack-ice is chiefly dependent on 

 that of the water on which it floats, it is not invariably so dependent. The eff'ect of wind may be 

 to set up a motion relative to that of the surface drift and this motion may at times be rather rapid. 

 It is, therefore, he says inconceivable, if the normal habitat of the youngest larvae should prove to 

 be directly below the ice, that they would never lose contact with it, from which it may be argued that 

 our persistent failure so far to capture them by surface nets either close to or actually inside the pack 

 must be attributed to the fact that these very young stages do not, as Ruud had supposed, exist in this 

 particular environment. As for Fraser's explanation it is now clear that whether the two Naupliar 

 stages are passed through with great rapidity or not the existence of the Second Nauplius at least is 

 not so ephemeral that it cannot be captured in very substantial numbers provided that in oceanic 

 water one searches deep enough for it. 



Although his data were not copious enough to allow him to visualise the full extent and finer detail 

 of the phenomenon of the climbing larvae Fraser in a measure foreshadowed it in the following 

 passage. ' Is it possible that the development of eggs of E. superba takes place in water which is 



^ But see p. 205. 



