446 DEPTHS OF THE OCEAN chap, vn 



Table B), we observe that northern (boreal) forms decrease 

 enormously to the west of the British Isles, We may say that 

 there is a sharp southern limit to the distribution of these 

 species west of the Channel ; the cod, saithe, tusk, and halibut 

 here quite cease to play any part in the captures. 



The northern limit for the southern forms is essentially 

 different. Of the species recorded in the systematic list of 

 bottom-fish captured by the " Michael Sars " in the Atlantic, 63 

 species were previously known from the Mediterranean, and are 

 found there in abundance. Of these only a few are genuine 

 southern forms; 10 species have their northern limit on the coast 

 of France, 19 on the coasts of the British Isles, and 23 occur 

 in varying numbers even on the coasts of Scandinavia. As we 

 shall show in Chapter X., this wide range of certain species is 

 probably due to the fact that the water- layers in the North 

 Atlantic run north, and transport especially the young stages of 

 certain southern species, which may as a consequence pass their 

 youth very far from the localities where they were born. This 

 is why the boreal fish-fauna is more or less mixed up with 

 southern forms, especially in the southern part of the boreal 

 region, for instance in the southern North Sea, in the areas 

 west of the British Isles, in the Kattegat, and along the coast of 

 the Skagerrack, in which localities high summer temperatures 

 prevail in the upper layers. 



To the south-west of the British Isles, from the Bay of Biscay 

 towards Morocco, we enter the real area of the southern fauna. 

 This is shown by the table containing the fishery statistics, as 

 well as by the record of the captures made by the " Michael Sars " 

 in the Atlantic. In the following list the captures made during 

 the cruise down to about 500 metres, or 300 fathoms, are 

 recorded and arranged in three groups : (i) West of the British 

 Isles, (2) West of Morocco, and (3) South of the Canaries. 



[Table 



