114 DISCOVERY REPORTS 



based on the assumption that the organisms whose diurnal movements one is attempting to portray 

 are evenly (or randomly) distributed throughout each depth interval traversed by the vertical nets. 

 But are the larvae of £■. superba in fact so disposed? It will be shown later (pp. 234-6) that there are 

 considerable grounds for supposing they are not, but, like the older stages (p. 149), are disposed in 

 shallow ' rafts ', no more than a yard or two thick, through which the nets in each instance pass perhaps 

 for only a second or two. Assuming such a disposition, and assuming too that only one such raft 

 existed in each vertical horizon, then the time correction applied in the case of the shorter-term 



TIME 



STATION 

 O- 



SO- 



100- 



250 



500- 



750 



1000- 

 N5 OF 

 METANAUPLII 



I400- 

 -1800 

 1104 2610 



O- 

 50- 

 100- 

 250- 

 500 

 750- 

 1000- 



I800 - 2200 

 1965 655 637 1144 1138 1545 2345 1671 2600 1713 1994 26031 



63 517 34 557 1515 195 I05I 10 106 5 8 830 



22O0 - 0200 

 1492 520 618 854 



I0200- 

 0600] 

 647 



24 6 20 184 



0600- lOOO 

 |WI97 638 823 



!?: 



115 7 43 



looo- 

 -woo 

 636 



+ 



TIME 

 STATION 



O 



-SO 



-lOO 



-250 



-500 



-750 



-lOOO 



N5 OF 

 METANAUPLII 



12 

 10 

 2 



II 

 52 

 95 



13 

 67 

 36 



- 13 9 3 



2 440 461 19 



21 1215 4720 116 



66 51 485 36 



2 53 245 78 



4 - 35 - 



5 

 112 

 63 

 39 

 41 

 lO 



167 

 115 



5 



I 



90 

 119 

 97 



4 



165 

 69 



2 

 31 

 47 

 20 

 22 



59 

 148 

 II 



10 

 6 



142 49 

 196 29 

 5 5 

 - 35 

 4 7 

 5 



351 - 



20 - 



94 36 



ISO 28 



282 2 

 7 



2 5 

 - 31 

 2 I 



O 

 SO 

 lOO 

 -250 

 500 

 7SO 

 lOOO 



Fig. 12. Four-hourly vertical distribution of the First Calyptopis based on the catch-figures shown in 

 Fig. 6 uncorrected (histogrammatically) for duration of haul. 



upper-level net hauls would be unnecessary since the nets in every instance of striking a raft would 

 strike it for only a second or two and so produce samples which, whether the haul were long or short, 

 would for all practical purposes be comparable. The four-hourly vertical distribution of the First 

 Calyptopis, when co-existent with Metanauplii in the plankton, might for all we can tell then be as 

 represented in Fig. 12 in which the catch-figures in Fig. 6 have been expressed graphically as they 

 stand without any conventional correction having been applied to the upper-level hauls as hitherto. 

 In this presentation of the data, which incidentally reveals even more emphatically than Fig. 6 does 

 the haphazard and unpredictable subsurface levels at which, regardless of hour, the non-free First 

 Calyptopis may be encountered, it will be seen that where significant numbers are involved, as for 

 instance at Stations 171 3, 1994, 620 and 618, the concentration of the larvae near or moderately near 

 the surface has not been recorded except in instances where the Metanauplii were scarce, leading one 

 to suspect that the moulting of the latter at these particular stations had taken place some considerable 

 time back in the past. 



Dr Fraser with whom I have closely discussed the whole question of the diurnal movements of the 

 larvae agrees that it is a complex one and that in so far as the First Calyptopis is concerned there can 

 be no satisfactory answer without there having first been separation of the deep climbers from those 

 that have reached the surface. He makes the following comments which I present with some slight 

 alteration in wording but not in sense. 



(i) Both Marr's and Eraser's method of presenting the vertical movements by histograms is inadequate to the 

 extent that it does not take into comparative account the very different order of numbers at different 4-hourly 

 periods. 



