166 THE FAUNA OF THE DEEP SEA 



selves lend support to the view that the fauna of 

 the deep sea has been derived from the fauna of 

 shallower water by successive migrations at different 

 periods of the world's history. Those that exhibit in 

 a most marked degree the special bathybial characters 

 are probably those whose immigration took place 

 long ago, whilst those more closely related to shallow- 

 water forms are, comparatively speaking, recent 

 importations. The occurrence of Scopelidae and 

 Sternoptychidae in deep water suggests, as Moseley 

 pointed out many years ago, that the fauna is partly 

 derived from the pelagic plankton. But while these 

 points may seemi clear to us, there are others that still 

 require much more investigation and consideration. 

 The whole question of the function and use of the 

 phosphorescent organs, the mucous glands, the 

 barbels and elongated fin rays, the mode of life, 

 the deposition of ova and their development, afford 

 problems which in the present state of our know- 

 ledge must remain unsolved. Let us hope that in 

 the future there may be a new stimulus given to 

 deep-sea research, and these problems may be again 

 seriously studied and eventually solved. 



