794 THE AMERICAN NATURALIST. [VoL XXXIII. 
Again, one of our own writers, Dr. Walter Faxon, in his 
work on the stalk-eyed Crustacea secured by the A/batross 
(p. 253), says, in reference to the red color of the deep-sea 
Crustacea: “This color, then, is to be regarded as entirely 
useless to its possessor,’ and concludes that because certain 
species turn red when placed in the dark, he can explain the 
red color of deep-sea forms as a purely physical result of their 
environment. 
Now I, for one, am unwilling to surrender the original Dar- 
winian proposition. Of course there are many things yet to be 
explained, or even inexplicable with our present knowledge. 
But this does not justify the unqualified use of such terms as 
“ meaningless” and “ useless.” 
It is the purpose of this paper to explain cases in which phos- 
phorescent light is emitted by animals, in terms of its use to 
the animals themselves. ; 
To this end we can conveniently divide the inhabitants of 
deep water into free-swimming and fixed forms. In the former 
class would be all of the fishes, nearly all of the Crustacea, most 
Mollusca, Vermes, and Echinodermata, part of the Ccelenterata, 
and most of the Protozoa. 
It will also simplify matters to remember that practically all 
deep-sea forms live on animal food. Among the fishes are 
several, allied to Lophius and Antennarius, which are provided 
with a bait said to be luminous, which serves to attract the 
prey. Others are luminous along the lateral line in definite 
spots. The utility in this case is not certainly known, but two 
suggestions may be made, one to the effect that the light 
attracts the mate and thus serves the purpose of attractive 
coloration ; the other that it attracts the prey and serves the 
purpose of alluring coloration. 
A very large number of crustaceans are phosphorescent, 
often brilliantly so. Many of these have large eyes, and are 
particularly active in movement and voracious in appetite. 
They feed on minute organisms, for the most part, and it can 
hardly be doubted that they often use their phosphorescent 
powers for the purpose of illuminating their surroundings 
and revealing their prey. Here again it is probable that the 
