NO. 6.] INTRODUCTION. 



As to the general character of the pelagic fauna in the North Polar Basin 

 explored by the Expedition, it exhibits, on the whole, a pronounced resemblance 

 to that of the North Atlantic Basin, the greater number of species having, 

 indeed, proved to be common to both. In considering the Calanoida in 

 particular, it was not a little surprising to find rather abundantly represented 

 in the samples, some characteristic forms well known to me from the deep 

 fjord-basins of the south and west coasts of Norway, but hardly ever recorded 

 by any foreign zoologists, though they must doubtless also occur in the North 

 Atlantic Basin. These forms, which have occasionally been mentioned by 

 me as deep-water Calanoida, are, indeed, at least off our coasts, only met 

 with in depths of more than 100 fathoms, whereas in the North Polar Basin 

 they often ascend to the very surface of the sea. Intermingled with them were 

 some well-known surface-Calanoids, such as the widely distributed Calanus 

 finmarchicus, Pseudocalanus elongatus, etc. There are, moreover, a 

 number of hitherto unknown forms, to be presently described in detail, which 

 accordingly might be regarded as peculiar to the Polar basin; but it is not 

 improbable that on a closer investigation, these forms will also be found to 

 occur in the northern part of the Atlantic basin. Indeed, strictly speaking, 

 the most westerly part of the 'Fram's' route lies on the border between the 

 two basins; and yet the character of the fauna here did not differ in any 

 essential manner from that in the eastern part. As, however, the superficial 

 current in the North Polar Sea has been clearly shown to flow in a westerly 

 direction, it is possible to suppose that some forms at least might have their 

 centre of distribution far east, perhaps even in the Bering Sea. But as 

 the pelagic fauna of that part of the ocean is still very imperfectly known, it 

 is as yet impossible to decide with certainty which forms in such cases 

 ought to be regarded as immigrants from the east. At any rate, though the 

 existence of the western current has been demonstrated in a most convincing 

 manner by the drift of the 'Fram', there is also full evidence of the existence 

 of a current in quite the opposite direction, but confined to the deeper strata 

 of the sea; for both the comparatively high temperature of the water found 

 down to the lowest depths and its great salinity clearly show it to be derived 

 from the Atlantic Basin. An immigration of animals to the North Polar Sea 

 may accordingly be possible from both the west and the east ; but, as the more 

 superficial strata flowing in a westerly direction, together with the ice covering 



