No. 394.] THE UTILITY OF PHOSPHORESCENCE. 797 
phorescent medusz. In the subtropical Atlantic hundreds of 
square miles of the surface are thickly strewn with a medusa, 
Linerges mercurius, which glows like a living coal at night. 
This species has eight marginal sense-bodies, and the phosphor- 
escence may well serve as a directive contrivance, aiding in the 
perpetuation of the species. 
In general, it.may be said that the phosphorescent powers 
possessed by free-swimming deep-sea forms can be accounted 
for in very much the same manner as their coloration, and serve 
much the same purposes as protective, aggressive, alluring, and 
directive colorations. 
We now come to a consideration of the uses of phosphores- 
cent powers in the second class of animals indicated at the 
beginning of this paper, namely, the fixed forms. 
Most of the phosphorescent organisms in this group belong 
to the subkingdom Ccelenterata. Among the Actinozoa the 
Pennatulidz are mentioned by several writers as being especially 
brilliant in their flashes of light. The gorgonians are also often 
phosphorescent, and Agassiz says: “Species living beyond 100 
fathoms may dwell, in total darkness, and be illuminated at 
times merely by the movements of abyssal fishes through the 
forests of phosphorescent alcyonarians.”’ 
Many authors have noted the light-emitting powers of numer- 
ous hydroids. These occur in great quantities over certain 
areas of the sea bottom, and must add considerably to the sum 
total of deep-sea light. 
It may, I think, be said that in general the fixed marine forms 
are not behind their free-swimming allies in either the quality 
or quantity of their light-producing powers. 
The question now before us is: “ = what use is this power 
to its fixed and sightless possessors ?’ 
Perhaps the most generally accepted opinion is that suggested 
by Verrill, who regards the phosphorescence as protective in 
function. Most Coelenterata, he argues, are possessed of 
nematocysts. Fishes are known in some instances to eat the 
polyps of colonial forms, and they might come to associate the 
phosphorescence with the nettling cells, and thereafter avoid 
those forms showing the danger signal. 
