198 



DISCOVERY REPORTS 



in daylight at which a series of two or more N ioo H nets were used Primno was taken 

 at twenty-three, and out of twenty-eight stations taken during hours of darkness Primno 

 was taken at six stations. Dr N. A. Mackintosh, who has worked with a larger quantity of 

 material collected over a wider area in the more recent surveys, and who has recently 

 published his results (1934), has found Primno to exhibit a migration the reverse of 

 that usual in zooplankton organisms, rising towards the upper layers in daylight. Our 

 figures tend to support this very interesting discovery, especially the fact that out of 

 these twenty-three stations at which it occurred during the day it was taken at the 

 surface at seven of them, whereas it was taken at the surface at night on only one 

 occasion. In the consecutive net series taken at the surface at St. 150, which started at 

 1700 o'clock, 3 hours before sunset, and proceeded until 0600 o'clock the following 

 morning, 2 hours after sunrise (0355), P. macropa does not appear in the nets until 

 that towed between 0300 and 0315 o'clock, and then it occurs in seven other hauls, all 

 of which are after sunrise. 



Table XXIII 



The depth distribution of Primno macropa as shown by the N 70 V nets 



The species has been taken in the Antarctic before by the Belgica (Monod, 1926) 

 Gauss (Spandl, 1927), and Terra Nova (Barnard, 1930) Expeditions; the first-named 

 taking it as far south as 71 ° 51' S, 87 27' W. 



Vibilia antarctica, Stebb. This species takes second place in importance amongst the 

 pelagic Amphipods of this region. It occurred at most stations, and at times was 

 moderately abundant. A complete record of its occurrence is given in Appendix II. 

 The largest catch was made with the N 100 H net at St. WS 69 across the line of Ant- 

 arctic Convergence towards the Falkland Islands, when 227 were taken near the surface ; 

 and at the next station, WS 70, eighty-four specimens were taken in the surface net. 



Its vertical range of distribution is shown in the following table based upon N 70 V 

 net results, when it is seen to inhabit the cold surface layer and a mixture of this water 

 with the warmer layer below down to a depth of 500 m. 



It exhibits a vertical diurnal migration towards the surface during the hours of 

 darkness; this phenomenon is discussed and illustrated on pp. 237 and 251. 



