698 DEPTHS OF THE OCEAN chap. 



of typical surface fish (Scopelidse, young fish), besides the 

 silvery fishes of the intermediate layer, the Sternoptychidse and 

 the Stomiatidae found mainly between 150 and 500 metres, live 

 just in the specifically light and thin water-layers (see Fig. 

 526, representing an adult Argyropeleais heinigyinmis, only 34 

 millimetres long, but with almost ripe ovaries). Excepting the 

 long ribbon-like Trachypteridse, Regalectts gles?ie, etc., these 

 minute fishes are, as far as we know, the principal if not the only 

 ones peculiar to these light water-layers. In the surface-layers 

 it is possible to recognise three distinct types: (i) the minute 

 Scopelidae ; (2) the larger oily fish like the sunfish ; and (3) the 

 species which live near solid floating objects, such as the 

 Sargasso fish. 



One meets exceedingly few large fish in the ocean belonging 

 to the good swimmers, for instance, mackerels, pilot fish, sword- 

 fish, and sharks. Little is really known about the distribution 

 of all these, but several of them spend at least some part of their 

 lives in coast waters. 

 Boreal A comparison of the fauna of the Norwegian Sea and that of 



pelagic life. |-}^g Atlantic is very interesting. We have seen in Chapter IX. 

 that numerous fishes which live mainly in the Atlantic have 

 been found in the Norwegian Sea as very rare visitors. From 

 the notes of Professor Collett, covering many decades, I have 

 given a list (see p. 643) recording the frequency of the 

 occurrence of these Atlantic forms. The most remarkable 

 feature is the fact that most of them have been found at 

 the very surface, or have drifted ashore and have been found 

 stranded on the beach. Among these fishes there are several 

 species, for instance those belonging to the genus Argyropeleais, 

 which live at 300 metres in the Atlantic and have not been 

 captured at these depths in the Norwegian Sea. Figs. 504-506 

 show that the lines of temperature, specific gravity, and viscosity 

 situated in 300 to 500 metres in the Sargasso Sea rise up to 

 the very surface as we approach the Norwegian Sea. In this 

 direction the Gulf Stream runs, at all events in the northern 

 part of the section. 



The facts pertaining to the occurrence of boreal species in 

 the Atlantic are just the reverse. In Chapter IX. we have 

 learnt that on our track from Newfoundland to Ireland we found 

 boreal species, Clione limacina, Aglajttha, Calan7cs, Euchc^ta, and 

 several others, at depths between 750 and 1000 metres, while 

 in the Sargasso Sea we took Calanus hyperboreus and E2ich(sta 

 at 1000 metres. At these depths we find the same specific 



