382 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
extremely uniform, and that it presented the greatest analogies with 
that of the Sea of Norway. A great number of species considered as 
characteristic of arctic waters are found equally in the waters of 
Atlantic origin which flow toward Spitzbergen. It is understood, 
moreover, that the slight variations in the salinity and temperatures 
which are observed in this latitude are not sufficient to produce any 
essential modification in the composition of the floating fauna. 
Now, if we compare the pelagic fauna of the polar basin, as far 
as it is now known to us, with that of the Sea of Greenland, such 
as the catches of the Belgica show us, and that of the Norwegian Sea 
explored actively during these last years by the Norwegian steamer 
Michael Sars, and finally with that of the Atlantic, there would 
appear conspicuously a general law of the distribution of the pelagic 
organisms. The superficial and intermediate fauna of the Sea of 
Greenland offers the greatest resemblance to that of the average 
depths of the Sea of Norway. A considerable number of species 
of the ice regions are found in the Atlantic, but only at considerable 
depth. Some are found even in the Tropics, showing thus the cos- 
mopolitan character of the plankton, but here they exist only at 
great depth. In other words, many of the organisms of the Sea 
of Greenland are abundant beyond the arctic waters properly called. 
Some are even universally distributed, but the level which they seek 
is proportionally as much more remote from the surface as the lati- 
tude is lower. Some forms are even known in the vicinity of both 
poles and frequent the neighborhood of the surface, in the midst of 
the ice of the Antarctic, as well as in the latitude of Greenland and 
Spitzbergen. They can be traced for a greater or less distance in 
the Temperate Zone to depths more or less profound, while they lose 
themselves in the abysses of the Tropics. 
At the same time that the organisms retreat progressively into 
the basins of the ocean they leave the shores. It results that the 
same form can frequent the littoral portions in the north and can, 
as a consequence, serve to characterize the coast water, while it ex- 
ists in the south only broader and becomes thus an excellent ind1- 
cator of oceanic waters. 
One sees, then, that the distribution of these pelagic organisms 
can teach us nothing on the subject of the action of marine currents. 
The existence in the depths of the basin of Skagerak of organisms 
which are habitually known in arctic latitudes is not due, as some 
(Cleve and Aurivillius) have stated, to the direct effect of transport 
by polar currents. It is explained by an entirely different law. The 
progressive retreat from the surface is occasioned by the more in- 
tense action of solar rays. 
This example suffices to show that profound biologic study of 
species ought necessarily to precede its geographic utilization, a 
