4io DISCOVERY REPORTS 



(2) Energetic daily migration but no extensive annual migration: Pleuromamma 

 robusta, Euphatisia triacantha, E. vallentini, E. frigida. 



(3) Normally inhabiting the surface layers, but with no effective daily migration and 

 no apparent annual migration: Sagitta gazelloe, Calanus propinquus (adults), Para- 

 themisto gaudichaudi. 



(4) Normally inhabiting the warm deep water, with no effective daily migration but 

 descending into slightly deeper water in winter: Sagitta maxima, S. planetoids, Eukrohnia 

 hamata f. antarctica and possibly Dimophyes arctica (which in summer is usually taken in 

 hauls from 250-100 m., and may actually live at the top of the warm deep water or the 

 bottom of the Antarctic surface water). 



(5) Scarce or irregularly occurring species whose distribution cannot at present be 

 definitely classified: Conchoecia hettacra, Primno macropa, Haloptilus oxycephalies, 

 Clione antarctica, Haloptilus ocellatus, Auricularia antarctica, Diphyes antarctica, 

 Sibogita borchgrevinki, Vanadis antarctica. 



Group 1 above includes the species of by far the greatest numerical importance in 

 8o° W. It must be supposed that they drift northwards in the surface waters in summer 

 and return southwards in the warm deep water in winter. 



Species in Group 2 appear to adjust their distribution by daily instead of annual 

 migrations between the surface layers and the deeper water. 



Species in Group 3 must have some other method of maintaining their normal range 

 of distribution. Reference must be made here to the recently published work of Fraser 

 (1936) on the young stages of Euphausia superba. This important species which forms the 

 food of whales in the Antarctic was unfortunately almost entirely absent from the 

 catches in 8o° W. Fraser shows that whereas the adults and adolescents are mainly 

 confined to the Antarctic surface water there is evidence that the gravid females descend 

 into deep water to lay eggs. The eggs, Nauplii and Metanauplii are normally found in 

 the warm deep water while the Calyptopis and early Furcilia stages undertake daily 

 migrations between the warm deep water and the Antarctic surface water. It is possible 

 therefore that the species listed above under Group 3 have some similar device by which 

 the return towards the south is effected only at an early stage in the life-cycle. 



There is no evidence as to how the circulation of species in Group 4 takes place. 

 Eggs or larvae might rise to the surface layer or conceivably even sink into the Antarctic 

 bottom water. There is no obvious explanation of the descent of these species into 

 slightly deeper water in winter. 



It must always be remembered that the main drift of the water in both the surface 

 and the warm deep layers is towards the east, and that the organisms (of Group 1) taken 

 in say the surface in 8o° W in December are not the same organisms nor the offspring 

 of the organisms which were there in deep water in the preceding September. They 

 must be supposed to have come from deep water somewhere far to the west, and pre- 

 sumably, as generation succeeds generation, they will work their way eastwards round 

 and round the Southern Ocean. It must also be remembered that neither the surface 

 water nor the warm deep water move steadily in a north-easterly and south-easterly 



