92 DISCOVERY REPORTS 



Rhincalanus gigas (Fig. 19). This species again can be taken in the greatest abundance 

 during the day, but on balance there seems to be some sort of variation. St. 461 and 

 Sts. 618-25, however, do not suggest any definite migration or variation. 



Pleuromamma robusta (Fig. 18). Of all species found in the Antarctic surface water, 

 this has on the whole the most pronounced diurnal variation. Examples occurred in only 

 three hauls out of 196 between 0600 and 1959. The vertical migration is shown very 

 clearly at St. 461. It appears to sink below 600 m. during the day, and rises to within 

 reach of the N 100 B only within a few hours of midnight. 



Metridia gerlachei (Fig. 18). Here again there is a strongly marked migration, but 

 specimens have occasionally been taken in daytime. At St. 461 there was a wide range 

 of vertical distribution, but the vertical migration was not well defined. 



Haloptilns ocellatus. This species occurred only once north of 6o° S. Specimens from 

 farther south show no sign of diurnal variation, and St. 461 suggests that there is no 

 vertical migration. 



Haloptilns sp. (Fig. 20). Occurrences are spread equally through the 24 hours, and 

 the figures from St. 461 suggest no vertical migration. 



Pareuchaeta sp. (Fig. 18). The diurnal variations are very clearly defined, and examples 

 are rarely taken during the hours of daylight. It is evident that this genus lives at a 

 considerable depth and comes within reach of the net only at night. This supposition 

 is confirmed by the catches at St. 461. 



Heterorhabdus sp. (Fig. 18). The genus is uncommon, but great variation obviously 

 takes place. St. 461 shows that it lives at a deep level but the series of hauls does not 

 bring out the vertical migration very clearly. 



Eucalanus sp. (Fig. 19). The material again is limited and the numbers in which the 

 species occurs are variable. There is evidently a certain amount of variation, but there have 

 been nearly as many occurrences in daytime as at night, and it is difficult to know what 

 would result from a larger body of data. A vigorous vertical migration is improbable. 



Enchirella sp. (Fig. 18). There is little material, but there is evidently a marked 

 variation. St. 461 shows a considerable amount of vertical migration. 



Candacia sp. (Fig. 18). This is another uncommon organism, but there is no question 

 that it is normally beyond the reach of the net during daytime. The few specimens 

 occurring at St. 461 were taken in the deepest nets. 



Parathemisto gaudichaudi (Fig. 19). There is only a slight variation, roughly equivalent 

 to that of Calanus acutus. Curiously enough Sts. 618-25 suggest quite a marked diurnal 

 variation. At successive stations the catches were as follows: 21, 4, 260, 7, 19, 8, 68, 1. 

 The alternate large catches were those from the night stations. It was absent from 

 St. 461 except for some doubtful juvenile stages. At all events this species has actually 

 been caught in both large and small numbers almost as often during the day as during 

 the night. 



Primno macropa (Fig. 20). The behaviour of this species is most remarkable. From 

 the figures for diurnal variation it seems impossible to avoid the conclusion that it rises 

 to the surface in the daytime and sinks at night, for although the species is of common 



