„6 DISCOVERY REPORTS 



free Calyptopes are concerned the average daytime gatherings in the top lOO metres, though some- 

 what smaller, are not significantly smaller, than the corresponding gatherings at this level at night,i 

 and that in so far as negative observations go, there are just as many, in fact rather more, at this level 

 at night as by day. The same can be said for the early Furcilias. There are it is true considerably 

 more negative daytime observations for Furcihas 4-6 than night-time ones, but clearly such positive 

 results as we have point to a pronounced concentration of these stages, both by night and by day, 

 in the top 50 m. In so far, however, as the Furcilias are concerned, especially the late Furcilias, it 

 might it seems be expected that there would be more negative observations (and on the average 

 smaller gatherings)^ in daylight than in darkness, for as Southern and Gardiner (p. 268) have shown 

 for the much smaller freshwater Crustacea of Lough Derg, avoidance of the nets in the ' upper illumi- 

 nated water layer ' in daylight is a factor that cannot be ignored. The average length of Furcilia 4 is 

 8-OI mm., of Furcilia 5, 9-52 mm. and of Furcilia 6, 11-34 J^"^- Towards the end of their life-span 

 the majority of Sixth Furcilias in fact grow to between 1 1 and 16 mm. long (Fraser, 1936, Appendix I). 

 And so we are dealing here not with such small and feeble organisms as copepods, ostracods and 

 water fleas, but with distinctly large and active animals. 



(4) It is true that no First Calyptopes (with Metanauplii co-existent in the plankton) are recorded 

 in daylight from 0600 to 1800 hr. in the top 100 m., but it is equally true (Fig. 6) that none or very 

 few are recorded at this level at Stations 1965, 637, 1671 and 2600 at 1800-2200 hr., and only 

 negligible numbers at Stations 855, 1144, 1545, 2346 and 2603 in the top 50 m. during the same 

 period. These stations, moreover, almost without exception were made in darkness, it being in the 

 latter part of the 1800-2200 hr. period that most, though not by any means all, of our night work was 

 done. The fact that we do not record the First Calyptopes at these high levels in these particular 

 instances is simply I think because, having only recently sprung from their deep Metanaupliar parents, 

 they are still reaching for the surface. In any case we do in fact find (Figs. 9 and 10) large numbers 

 of Calyptopes 1-3 crowding the surface zone, especially the top 50 m., at all hours of the day and night, 

 when the disturbing influence of the deep moulting Metanauplii has been removed. 



(5) This again is true, as it is indeed for the Second and Third Calyptopes, but the numbers 

 involved (Figs. 9 and 10), relative to those above 100 m., are in general small and suggest as I 

 have already noted (p. iii) that such Calyptopes as do go down by day represent only a minor part 

 of the total surface population. 



(6) Again perhaps I should ask how else are we to express the actual results? We can seldom 

 ' prove ' anything in marine biology and if we do, sooner or later something or someone turns up to 

 disprove it, which is perhaps all to the good. In general, or at best, we can only point to what seems 

 to be taking place ; and it seems to me obvious that many of the deep First Calyptopes in Fig. 8 are in 

 fact larvae that have never been at the surface, having only recently escaped from their Metanaupliar 

 husks. Fig. 8 is based on Fig. 6 and this in turn on the basic data presented in Tables 13 and 14 

 (p. 90) and these, with their explanatory footnotes, provide it seems incontrovertible evidence that 

 the deep Calyptopes captured along with Metanauplii in the same nets were in fact in the process of 

 emerging from their Metanaupliar parents, or had only recently sprung from them. There is every 

 reason too to suppose that the Calyptopes taken immediately above the zone of Metanaupliar 

 abundance (i.e. immediately above 500m.), as for instance (Fig.6) at Stations 1965, 637, 1138, 1545, 

 1671, 2600, 2603, 647, WS 197, 638 and 636, had also only recently sprung from their Metanaupliar 

 forbears, had never in fact been near the surface, but were still reaching for it both by night and 

 by day. 



^ Our average daytime gatherings for Furcilias 1-3 between 100 m. and the surface are actually larger than our night ones. 

 * This seems to apply with particular emphasis to the relatively large Furcilias 4-6. 



