i66 DISCOVERY REPORTS 



well in fact be only an appearance since in the darkness, in spite of all precaution, some euphausians 

 might readily have got into the nets as, shot open, they were being passed through the densely popu- 

 lated surface zone. 



Table 34. Measurements of the krill in the 10 and 22 month old swarms sampled on the surface 

 at Station 1835, older swarms in roman type, younger swarms in italics 



Other Discovery stations, notably Stations 207 and 461, at which consecutive nets were used, reveal 

 an equally pronounced massing of the young krill at the surface regardless of hour or light (Hardy, 

 iq;5; Fraser, 1936, Fig. 74). At Station 461, however, there seems to have been marked con- 

 tamination of the subsurface samples (Fraser, 1936, Appendix II), again significantly the night 

 samples, owing to the multiple net-flights used. 



The diurnal vertical distribution of the older swarms is evidently very much the same as for the 

 younger except that the day and night massing of the former near the surface is much more difficult 

 to demonstrate simply because the larger krill (p. 262, Table 53), in broad daylight especially, tend 

 to avoid the surface nets much more easily than the smaller are able to do. It seems, however, that 

 it must inevitably be concluded from the complete subsurface void revealed by the closing nets from 

 daylight to dusk (Table 33, series {a)) that the 22 month old swarms must in fact have been present 

 on the surface, not only from sunset to darkness (Table 34), but from beginning to end of the opera- 

 tions conducted on this occasion, and that the negative, insignificant or minor catches recorded on the 



