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. 
