In general pelagic fauna in the Polar Sea resembles that of the northern Atlantic basin, the greater number of species being common to both. While several heretofore unknown forms collected by this expedition may be peculiar to the polar basin, yet it is not improbable that these forms also occur in the North Atlantic. This appears probable, since the western part of the _Fram’s_ route lies on the border of the two basins, where the fauna does not differ essentially from that in the eastern part. While the pelagic fauna of the Polar Sea, even in the lowest depths, resembles that of the Atlantic basin, the great salinity of its water clearly indicates that it comes from the North Atlantic, and it is therefore more than probable that the migration of pelagic animals to the North Polar Sea is also from the west. Indeed, Doctor Sars is of the opinion that the greater part of the pelagic life of the north-polar basin comes by the underlying easterly current from the North Atlantic. On the other hand, it is evident that the westerly-flowing surface current of the Siberian Sea is of vital importance as a means of supplying nourishment to the marine animals of the western Arctic Ocean. This food supply, microscopic algæ chiefly _Diatomeae_, while very abundant on the surface of the Siberian Sea, diminishes gradually towards the west. “Indeed,” says Sars, “without such a constant conveyance of nourishing matter, there could be no such rich animal life in the Polar Sea.” A very remarkable fact was the presence of certain pelagic _Copepoda_, which hitherto had only been observed in southern waters, and a _Calanoid_ of the genus _Hemicalanus_ Claus, previously known only from the Mediterranean and tropical parts of the Atlantic and Pacific oceans. Two species of the genus _Oncoea_, which accord perfectly with species in the Bay of Naples, were found in great abundance north of the New Siberian Islands. Another copepod, of the genus _Lubbockia_ Claus, heretofore only known in the Mediterranean and tropical oceans, was found in the same locality, with which was a small perfectly hyaline copepod of the very remarkable genus _Mormonilla_, of which heretofore only two species have been recorded, both in the tropical Pacific and south of the equator. Perhaps the most remarkable forms are those mentioned by Doctor Sars, when he says: “The very close and apparently genetic relationship between the two polar species of the amphipodous genus _Pseudalibrotos_ and those occurring in the Caspian Sea, is another remarkable instance which seems fully to corroborate the correctness of the assumption of geologists as to a direct connexion in olden times between this isolated basin and the North Polar Sea.” Both species, taken near 85° N., are regarded as the primitive types from which the Caspian forms are descended. The more remarkable of the Arctic forms, _P. Nanseni_, is reproduced on page 430.