THE LARVAL STAGES 117 



(7) I was compelled to combine the Calyptopis stages in Fig. 9, just as I was for the Furcilia stages, 

 because all earlier attempts to present the vertical movements by single stages broke down for lack 

 of numbers.^ 



(8) This is true, but I question the significance of fifty-five rather deep specimens, the majority, 

 however, in the Antarctic surface layer, at 1 400-1 800 hr. when one thinks of the fantastic numbers 

 that must go to make up the Calyptopis (even the free First Calyptopis) population, and remembers 

 that these fifty-five do not come from a single station but are in fact our total harvest from forty-six. 

 The concentration recorded from 250 m. to the surface at 0600-1000 hr. is densest it will be seen 

 between 100 and 50 m. and it does not upset my views that such vertical movements as the larvae 

 undertake (i) do not involve the whole of the surface population, (2) are confined for all practical 

 purposes to the Antarctic surface layer, and (3) do not involve them in a mass descent into the 

 counter-flowing deep current during the daylight hours. 



(9) This is the crux of the whole matter and to avoid repetition I would refer the reader to begin 

 with to my remarks in (6). Clearly what Dr Fraser has in mind here is that at many, although obviously 

 not all, of the stations in Fig. 6 there could in fact be two distinct groups of First Calyptopes, the 

 deeper between 1000 and 500 m. obviously still climbing, the shallower, between say 500 and 100 m., 

 not climbers, but larvae that, having long since perhaps reached the surface, had returned to deeper 

 daytime [and it could also be argued night-time] levels. This I agree is a distinct possibility, but 

 I would point out that if it be true it would often seem to be involving the First Calyptopis in a 

 massive night-time migration into deep, sometimes very deep, water, in other words in a paradoxical 

 movement distinctly at variance with the ' orthodox '^ pattern we have come to recognise as typical of 

 rhythmic diurnal migration. In view of this I think there can be at least some assessment of the effect 

 the climbers are having on the migration pattern of the larvae at higher levels, and I therefore conclude 

 that on the whole it is safer, especially in view of the migrational pattern in Fig. 9 and of my remarks 

 in (6), to regard all First Calyptopes recorded at stations where Metanauplii were also taken, as 

 travellers from deep water, the majority of them (Fig. 6) still reaching for the surface, their ultimate 

 goal, a minority (as for instance at Stations 1944, 1492, 854 and 647) having actually accomplished, or 

 almost accomplished, perhaps only recently,^ their long journey from the depths where they were 

 born. I do not, it is true, know the rate of ascent of the climbing Calyptopis, but I have suggested 

 (p. 120) on physiological grounds that it might be very slow. And so it could well be (see again Fig. 6) 

 that those taken in the 500-250 m. layer (or even still higher) are still on their way to the surface and 

 have not yet, as Dr Fraser puts it, been ' resident ' there. Nor do I know the duration of the First 

 Calyptopis stage, but again I have suggested (p. 314), from what little we know of the northern 

 euphausians, that it might last 7 days or even longer.* The occurrence, rare though it be, of pure, 

 or almost pure, cultures of First Calyptopes at the surface, as for instance (Table 1 5) at Station 2280, 

 without any trace of a climbing population feeding them from below, is also suggestive of a rather pro- 

 longed existence in the First Calyptopis stage. For such larvae would already have climbed about 

 1000 m. and for all we know may have been in the surface zone for some considerable time before our 

 searching nets came across them. Moreover, Station 2280 lies far out in the West Wind drift, a region 

 in which we have never, except for one exceptional instance (Table 13, Station 647), struck the larvae 

 rising from below. The Calyptopes encountered there it seems (p. 3 1 5) must have surfaced much farther 



^ In his presentation of the vertical movements of the Furcilias Dr Fraser, with far smaller numbers than I had, combines 

 Furcilias 2-4 and Furcilias 5 and 6. 



^ I use the word guardedly, for in the science of the sea what is orthodox today may well prove to be unorthodox tomorrow. 



^ In the sense that our nets were perhaps striking these concentrations soon after their arrival in the surface zone. 



* There is evidence (p. 314) from the earliest major appearances of the First and Third Calytopes at the surface in 

 Weddell West that it might well last this long. 



