Luminosity of Marine Animals. 
74i 
1885.] 
elicited by rubbing the surface, which contains a minute 
trace of the luminous matter, points decidedly to other 
causes as co-operating. This function is plainly referrible 
to the organic chemical affinities of the tissues concerned. 
On the other hand, in certain Annelida it is a purely nervous 
activity, probably of kin to that which produces heat. 
With the exception of Macartney, former authors have 
generally sought to connebt the emission of light with the 
peculiar conditions of the depths of the sea. It was as- 
sumed that total darkness prevailed at the depth of 1000 feet, 
and that the phosphorescence of marine animals was for 
them a substitute for the light of the sun. It was further 
supposed that these lights were a guide to animals 111 seeking 
and attacking their prey, whilst, on the other hand, the 
power of withdrawing their light enabled them to escape 
dangers. It is well known that fish prey by night, and it 
was assumed that they were guided by the phosphorescence 
of their booty, since the light is particularly strong in those 
low animal forms which, by reason of their astonishing re- 
productive powers and of their dull sensibility, — little 
exceeding that of plants, — seem to be especially created for 
the nutriment of the higher forms. But with such theories 
great caution is necessary. 
In the first place, the phosphorescent animals do not seem 
to be more numerous in the depths of the ocean than be- 
tween high and low water-mark, or on the surface. On the 
contrary, the surface probably displays the greatest deve- 
lopment of luminous species. Very many young animals 
which are said to phosphoresce strongly become surface- 
forms soon after leaving the egg, and people thus in their 
different stages all three regions, — the surface, the mean 
depths, and the abysses. 
An examination of the life-histories of several phosphor- 
escent groups does not supply any useful data for establishing 
a theory of the funbtion of phosphorescence, especially with 
reference to nutrition. No phosphorescent form is more 
generally devoured by fishes and other animals than those 
which are non-phosphorescent. On the other hand, forms 
endowed with luminosity, if otherwise eatable, do not seem 
to escape capture. An examination of the stomachs of 
fishes proves this clearly, except perhaps the herring, which 
is pre-eminently a surface-fish. It is also not proven that 
such animals are always luminous, for many display a light 
only on irritation. 
The irregularity of the appearance of phosphorescence in 
animals which agree in every respebt in structure and habits 
