24 COLOUR IN NATURE chap, i 



Alcyonarians have been described as forming luminous 

 forests in the ocean depths, but Agassiz, Panceri, 

 and others insist that in the cases studied by them, 

 the luminosity is dependent upon mechanical and 

 chemical stimuli, and we are always being told of 

 the calm stillness of the ocean abysses. The swim- 

 ming of fishes among these forests may set up 

 currents which produce luminous flashes, but surely 

 those elaborate hypotheses which assume that the 

 Alcyonarians give sufficient light for the other organ- 

 isms to see each other's colours by, are a "baseless 

 fabric " of the imagination. 



With regard to the phosphorescence of the deep- 

 sea fishes, it is interesting to note that Agassiz 

 considers it to be a characteristic of these abyssal 

 fishes which belong to groups, most of whose 

 members are pelagic, rather than of abyssal fishes 

 in general. 



As to the meaning of phosphorescence little can 

 be said. It appears not improbable that like pig- 

 ments it may arise in different ways in different 

 organisms. It is at least difficult to believe that 

 a process like that described by Emery for Luciola, 

 which seems to be purely excretory, can be entirely 

 homologous with the luminosity of nervous structures. 

 The luminous substance in all cases is apparently of 

 the nature of a fat, and it is unnecessary to emphasise 

 the fact that complex fatty substances tend to occur 

 in association with nerve tissues. 



The subject has an important bearing upon the 

 general one, for phosphorescence, no less than 

 colour, has been frequently dismissed with a few 

 magic words upon Natural Selection. 



