,o8 DISCOVERY REPORTS 



they did, before, concentrations of First Calyptopes confined exclusively to great depths will prove 



in the long run to be of just as common occurrence during the darkest as during the brightest hours 



of the day. 



It follows from the foregoing that any attempt to illustrate the diurnal vertical movements of the 

 First Calyptopis, if it be based as in Fig. 8 (or as by Fraser in his Fig. 33) exclusively upon stations 

 where deep Metanauplii are moulting, or any attempt whatsoever that fails to take account of the 



I400-I800 IBOO-2200 2200-0200 O2O0-O60O 0600-IOOO IOOO-I400 



0-1 



SO 



100 



250- 



500 



750 



lOOO-J 



SOO 



1000 



Fig. 8. Pseudo-diurnal vertical migration. The four-hourly vertical distribution of the First Calyptopis 

 based on the aggregate of the catch-figures shown in Fig.^6. 



disturbing influence of the deep moulting of the Metanauplius upon the results, must end up in a 

 picture that in some respects is illusory. For such an illustration must inevitably include large 

 numbers of larvae which, although to all appearances migrants into deep water from the surface, 

 could never in fact have been anywhere near the surface at all. Fig. 8 in short provides a typical 

 example of the many pitfalls oceanography falls heir to through the employment of nets that do not 

 go deep enough. For if the lower limit of observation in this instance had been say 500 m. there 

 would have been no reason to suppose that the orthodox pattern of rhythmic diurnal vertical 

 migration it manifestly presents was anything other than real, or to doubt that the First Calyptopis 

 made a daily descent into the warm south-flowing core of the deep current running counter to the 

 surface stream. That the picture is not in fact real, but partly an illusion created by the presence of 

 recently born, and still climbing First Calyptopes rising from below, can clearly be established if the 

 dawn to dawn vertical distribution of the combined Calyptopis stages be based, as in Fig. 9, upon 

 data drawn from stations where the First Calyptopis^ occurred free, that is, not in association with 

 deep-mouhing Metanauplii, thereby excluding any possibility that deep, still climbing, Calyptopes 

 could enter into and prejudice the resuh and making reasonably sure that the Calyptopes as a whole, 

 the developmental ascent having been accomplished, had definitely reached the surface. Worked out 

 in this way the vertical extent of the diurnal movement, if in fact it can be described as such, of the 

 1 But not the Second and Third, since neither, except in apparently one rare instance (p. 90, Table 13, Station 1138, 

 footnote t), not included in the construction of Fig. 9, is involved in the developmental ascent. 



