THE RELATIONS OF THE ABYSMAL ZONE 57 



of the naturalists who have followed him in this line 

 of work, and the recent results of the ' Albatross ' in 

 comparing the deep-sea fauna of the eastern and 

 western sides of the isthmus of Panama seem if any- 

 thing to support it, we can take it as a point in 

 favour of his view of the origin of the abysmal fauna. 



It is impossible to say at present at what time in 

 the world's history these migrations commenced, but, 

 as Agassiz points out, none of the palaeozoic forms 

 are found in the deep sea, and this seems to indicate 

 that the fauna did not commence its existence earlier 

 than the cretaceous period. 



It is quite possible, however, that part of the fauna 

 of the deep sea has been derived directly from the 

 pelagic zone. The occurrence of bathybial Radiolaria, 

 Foraminifera and Siphonophora, and among fishes 

 genera and species of the pelagic families Sternopty- 

 chidas and Scopelidas, suggest that this zone may have 

 contributed very largely to the fauna of the abyss. 



Much of course still remains to be done before 

 we can consider any of these interesting problems 

 connected with the deep-sea fauna to be definitely 

 solved. All we can do at present is to speculate 

 upon the direction in which the facts at our disposal 

 seem to point, and by following up one clue after 



