UNEVENNESS OF OCEANIC PLANKTON 521 



quantities of Copepoda which were recorded with symbols indicating "few", "fair 

 numbers" and "many". Both they and the Euphausiacea show evidence of vertical 

 migration. It is possible that the increase in the Copepoda in Records 4 and 5 in the 

 evening and the morning may indicate a vertical migration. Between 1700 and 1800 a 

 number may have risen from below and be crossing the path of the recorder (20 m. 

 depth), remaining above the recorder during the night and again (their representatives 

 further on) sinking across the path of a recorder in the morning between 0700 and 0900. 



Record 7 



Date: 6-7. ii. 26. 



Time: 1550-0835. 



Position : 39 12' S, 15 20' W to 40 22' S, 16 36' W. 



Distance by ship's log: 91 miles. 



This record is interesting for its distribution of Salpa and Limacina shown in Fig. 7. 

 The numbers of Salpa fluctuate in a series of waves with main peaks at sections 7, 12, 

 19, 22 and 26, approximately 10, 14, 6 and 8 miles apart. There are lesser peaks in 

 between and there is a gradual increase in abundance up to section 26 and then a rapid 

 decline in numbers. Considered in relation to the time scale this increase suggests the 

 upward vertical migration of the animal, patchy in distribution, coming more and more 

 into the path of the instrument to reach a maximum after midnight and then sink more 

 rapidly in the early morning. The small increases at sections 2 and 35 might thus re- 

 present the fringes of larger concentrations lower down. This suggested vertical migra- 

 tion of patches is indicated in a diagram below the graph in Fig. 7 and should be com- 

 pared with the figure of vertical migration of Salpa fusiformis in Hardy and Gunther 

 (1935, fig. 123). Also the size of the patches is similar to that found for S. fusiformis at 

 South Georgia by consecutive net observations (loc. cit., fig. 135). This combined effect 

 of vertical migration and patchiness was suggested by Hardy and Gunther to account 

 for the distribution of Euphausia superba in the consecutive net series (loc. cit., fig. 136). 



The pteropod Limacina occurred in an isolated patch some 16 miles across, increasing 

 in concentration towards its centre. Such isolated patches of Limacina, as we shall see, 

 are not uncommon features of the oceanic plankton. The distribution of young 

 Euphausiacea is also shown in Fig. 7. The copepod population was exceedingly scanty, 

 never exceeding four per section. Chaetognatha, Ostracoda, Amphipoda, decapod 

 larvae and postlarval fish occurred in small numbers. 



Records 8, 9 and 10 



Dates: 9-13. ii. 26. 



Times: see Fig. 8. 



Position: 44° 03' S, 20 20' W to 52° 52' S, 34 03' W. 



Distance: 196-9 miles (see Fig. 8). 



Except for a break in record 8 (2235-0735 o'clock) and between records 9 and 10, 

 when deep-water nets were being used, the three records form a continuous series. 

 The main features are shown in Fig. 8. A single isolated concentration of Ostracoda 



