796 THE AMERICAN NATURALIST.  [VOL. XXXIII. 
subkingdom, and it is among these that we encounter amazing 
displays of the “living light.’’ The most brilliant exhibition 
of phosphorescence that I have seen was caused by immense num- 
bers of ctenophores in Bahia Honda, Cuba. The animals kept 
in a compact body and produced a maze of intertwining circles 
of vivid light. These animals have so-called ‘‘eye-spots”” and 
seem to be able to distinguish light. The phosphorescence may 
serve to keep them together, and thus effect the same end as 
“ directive coloration ” among vertebrates and insects. 
It is worth noting that blind species of groups normally pos- 
sessed of eyes are seldom if ever phosphorescent, a fact that 
seems further to enforce the idea that phosphorescence is used 
in connection with the power of vision, and probably serves as 
an aid thereto. 
Although Noctiluca and other allied phosphorescent Protozoa 
are more properly pelagic than deep-sea forms, they may occur 
at considerable depths, and thus come within the province of 
this discussion. These differ from the organisms hitherto men- 
tioned in that they have no recognized organs of sight, and, 
further, in their extreme simplicity of organization. Like most 
if not all Protozoa, they occur in enormous swarms and have 
some means of keeping together, as is necessary in the case of 
all forms that conjugate as a preliminary to reproduction, as do 
the ones under discussion. They are propelled by flagella and 
appear to control their own movements. At first thought one 
is at a loss to explain the phosphorescence of these eyeless free- 
swimming forms, but a little reflection will show a probable 
explanation. Although eyeless, many Protozoa have been 
proved to be sensitive to light, both natural and artificial. Any 
one who has worked with these lowly forms has noticed that each 
species has a preference for either the light or the dark side of 
the jar in which it is confined. Indeed it is practically cer- 
tain that sensibility to light is a fundamental property of simple 
protoplasm. This being true, it is easy to conceive of the 
phosphorescence of Noctiluca and its allies as directive in func- 
tion, thus aiding them in finding each other for the purpose of 
conjugation and the perpetuation of their kind. 
This same explanation may be applied to many of the phos- 
