May 31, 1901.] 
There is another line of evidence tending 
to prove the presence of light at the sea 
bottom, and this is the fact that most of the 
vertebrates inhabiting the depths have func- 
tional eyes, often more highly developed 
than in shallow water, and only exception- 
ally are the eyes aborted or absent. Dr. 
Alexander Agassiz has the following to say 
on this point: 
‘¢ We should not forget, on the one hand, 
that blind Crustacea and other marine in- 
vertebrates without eyes, or with rudimen- 
tary organs of vision, have been dredged 
from a depth of less than 200 fathoms, and, 
on the other, that the fauna as a whole is 
not blind, as in caves, but that by far the 
majority of animals living at a depth of 
about 2,000 fathoms have eyes either like 
their allies of shallow water, or else rudi- 
mentary or sometimes very large, as in the 
huge eyes developed out of all proportion in 
some of the abyssal crustaceans and fishes.”’ 
And Professor Verrill says: ‘ That light 
of some kind and in considerable amount 
actually exists at depths below 2,000 
fathoms may be regarded as certain. This 
is shown by the presence of well-developed 
eyes in most of the fishes, all of the cephalo- 
pods, most of the decapod crustacea, and in 
some species of other groups. In many of 
these animals the eyes are relatively larger 
than in the allied shallow-water species. ”’ 
In view of the almost uniformly blind 
condition of cave animals on the one hand, 
and of the well-tested Darwinian doctrine 
that useless structures, unless rudimentary, 
do not exist, on the other, I think we are 
justified in saying that a study of the col- 
oration of the deep-sea animals, in connec- 
tion with the general presence of functional 
eyes, is reasonable proof that light in ap- 
preciable quantities exists even at the great- 
est oceanic depths. 
This being granted, we naturally turn to 
a consideration of the question: What is 
the nature of this abyssal light ? 
SCIENCE. 
849 
As already intimated, it is incredible that 
sunlight could penetrate in appreciable 
quantities to any such depth as 2,000 
fathoms or over, or even to one-tenth of 
that depth, notwithstanding the theory ad- 
vanced by Verrill, who seems to consider 
the presence of sunlight necessary to ex- 
plain the facts of coloration. I think we 
are safe in assuming with Agassiz that at 
200 fathoms the light from the sun is pos- 
sibly that of a brilliant starlight night, and 
we are also justified in concluding that 
coloration would be useless in such a light. 
Did you ever notice how little of color can 
be seen even in the clearest moonlight night? 
Sunlight being out of the question, is 
there evidence of any other light that would 
satisfy the conditions of coloration ‘and or- 
gans of vision already referred to? 
I have, on other occasions, sought to col- 
lect the evidence of ithe cxistcrce of alyssa 
light, and to determine‘its nature and func- 
tion in the life economy of the deep sea. 
These efforts resulted in the belief that the 
light sought for is a phosphorescent light, 
and that it is adequate to explain the phe- 
nomena, already discussed in connection 
with the colors of deep-sea animals. 
This idea has been suggested before by 
several writers, notably by Andrew Murray, 
of the Challenger, but it has heretofore been 
only a suggestion which no one has taken 
the pains to seriously investigate. It will 
be of interest, therefore, to consider the ex- 
tent to which phosphorescent life is charac- 
teristic of the deep sea. 
For the purposes of the discussion we 
will divide the animals of the sea bottom 
into two classes, the free swimming and the 
fixed forms. 
Considering the free swimming forms 
first, we find among the fishes several allied 
to Lophius and Antennarius, which are pro- 
vided with a bait said to be luminous, 
which serves to attract the prey. Others 
are luminous along the lateral line in defi- 
