704 DEPTHS OF THE OCEAN 



From this it does not seem that such migrations as those 

 mentioned above are due to changes in temperature and 

 viscosity alone. We must, for the present, suppose that the 

 animals have the power of actively altering their level in the 

 water-layers. Ostwald's observations on the viscosity of sea- 

 water, and on the floating capacity of organisms, should render 

 these questions easier of solution, and their further investigation 

 should form a very interesting object for future expeditions. 



Effect of The currents of the ocean exert a very strong influence on 



Q^^lhT ^^^ distribution of many animals. All seafaring men and the 

 distribution inhabitants of all shores have known for ages that drifting 

 objects are carried very far by the currents of the sea, and that 

 "rare " and strange animals are stranded on the coasts. Along 

 the entire coast of Norway, even up to the Barentz Sea, drifting 

 objects and stranded fish are found, which really belong to the 

 distant warm Atlantic. Numerous accounts of the passive 

 migrations of animals through currents are to be found in 

 literature, many of them valuable notwithstanding the fact that 

 these conditions have only exceptionally been made the subject 

 of systematic investigation. 



Looking at the current-chart (Fig. 508), we see that the 

 central part of the North Atlantic, south of a line drawn from 

 the Bay of Biscay to the northern United States, forms a 

 separate current-system. The branch of the Gulf Stream 

 flowing north-east towards the coasts of northern Europe 

 receives an admixture of cold water from the Labrador current, 

 and also large volumes of water, as well as numerous organisms, 

 from the main body of the Gulf Stream. Entering the 

 Norwegian Sea this branch of the Gulf Stream runs through 

 the Faroe-Shetland Channel, sending off one branch to the 

 North Sea and another branch along the coast of Norway right 

 up to the Barentz Sea. This current system enables us to 

 understand many of the laws governing the distribution of 

 pelagic forms as referred to in Chapter IX. Thus the warm- 

 water fauna of the North Atlantic belongs mainly to the 

 central current system ; isolated specimens belonging to this 

 fauna not only occur in the north European Gulf Stream, but 

 are found in the Norwegian Sea, and on the northernmost 

 coasts of Norway (see the discussion of the distribution of 

 pelagic fishes in depths between 150 and 500 metres in the 

 Atlantic, and the occurrence of Atlantic fishes in the Norwegian 

 Sea, p. 644). The distribution of the animals of the coast banks 



