236 DISCOVERY REPORTS 



an asterisk in Fig. 103, should be disregarded in considering the normal migration, for 

 this station is beyond the line of Antarctic Convergence, where the Antarctic water has 

 dipped down below the sub-Antarctic water. At St. 41 (Fig. 106) the migration was 

 marked, likewise in the results from the consideration of the average percentage vertical 

 distribution at the deep water stations, but not so at the shallow water stations; this 

 provides a confirmation of its irregular behaviour. 



Calanus acutus, whilst showing considerable variation in its vertical distribution at 

 different stations, shows no regular diurnal migration. This is well shown in Fig. r?>8, 

 where the continuous line connects the positions of the net hauls containing the greatest 

 numbers at each station ; although actually more are taken at the surface at night than 

 in the daytime no regular migration can be detected. This is confirmed by the results 

 of the other two methods shown in Fig. 1 1 1 ; the average night and day distribution at 

 the shallow stations is the reverse of that at the deep-water stations, showing that the 

 variations in depth distribution are not regular diurnal ones, and the results from St. 41 

 show no upward movement at all. These specific differences in behaviour within the 

 genus Calanus are interesting, and will be referred to again in Part V of the report 

 (p. 312). We saw that C. simillimus approached Drepanopus pectinatus in behaviour; 

 Calanus acutus is similar in behaviour to Rhincalanus gigM and Oithona frigida ; the 

 figures illustrating these species are shown in juxtaposition for comparison. 



Rhincalanus gigas comes into the toj^o m. of water. Whilst there appears to be some 

 vertical movement apparent in the observation at St. 41 (Fig. 112), it does not represent 

 a regular rise and fall with the approach of darkness, and^f ^j.from the other two 

 methods (Figs. 112 and 409) show clearly that this species 49 Hfctrue diurnal vertical 

 migration. ^E* 



Clausocalanus laticeps, which was not taken in sufficient numbers in the N 70 V nets 

 to allow the first two methods of investigation to be used, shows in the N 70 H results 

 (Fig. 105) a most definite and gradual rise and fall from below 100 m. to the surface. 

 It begins its journey upwards soon after 1700 o'clock, and reaches the surface just 

 before midnight, and falls again at 0300 o'clock. 



Ctenocalanus vanus displays a diurnal migration, Figs. 104 and 107, but like Calanus 

 propinquus it is by no means regular in its behaviour, although it tends to come to the 

 surface in large numbers between midnight and 0200 o'clock. 



Drepanopus pectinatns, shown in Figs. 100 and 102, has a marked vertical migration 

 similar in character to that of Calanus simillimus, although it remains longer at the 

 surface in t^ early hours of the morning. It remains near the surface for a longer 

 period than any other species investigated by us, and together with C. simillimus arrives 

 at the surface earlier than any other Arm. 



Pareuchaeta antarctica (Fig. 120), Scolpithricella minor (Figs. 115 and 116), Pleuro- 

 mamma^obusta (Fig. 119), Metridia gerlachei (Figs. 115 and 117) and M. lucens (Figs. 

 115 and 118) are all forms inhabiting deeper water in the daytime but making a rapid 



