Luminous Organs of Fish — Haneda 
215 
ter. In addition to the serial luminous organs 
on the body there may be luminous organs 
on the jaws and near the eye. The more com- 
plex postocular organ of the Stomiatidae is 
freely movable, and can be rolled inward 
when not required. 
In the families Stomiatidae and Malacos- 
teidae there is a barbel which, in Diplolych- 
nus, is luminous at the end. In many other 
species, however, it is not certain whether this 
barbel is luminous or not. 
Deep-sea angler fishes have a luminous 
antenna. Lamprotoxus has a closed loop of 
luminous tissue on each side of the body be- 
tween the head and pelvic region, while 
in Eurypharynx and Saccopharynx there is a 
looped luminous organ which extends along 
each side of the dorsal fin as far as its poste- 
rior extremity, beginning either just behind 
the skull or just in front of the anterior ex- 
tremity of the fin. There is a half-moon- 
shaped luminous organ which is freely mov- 
able and which can be rolled inside situated 
below the eye in Anomalops. Photoble- 
pharon can shut off the luminous part of the 
organ by lowering a black membrane which 
functions like an eyelid. A species of Dolt- 
chop ter yx has a luminous organ on the ball 
of the eye in front of the lens. Monocentris 
japonicus has a pair of luminous organs on 
the end of the jaws. Some species of the 
families Gadidae and Macrouridae possess a 
luminous organ ventrally® in front of the 
anus. 
All of these mentioned luminous organs 
are of the direct emission type. That is, their 
luminescence is emitted directly from the 
source ( the luminous body ) and remains 
more or less concentrated or focused at one 
point without much diffusion. 
Some luminous fishes show no outward 
peculiarities in structure or appearance and 
resemble ordinary non- luminous fish. This is 
because the luminous body lies inside the fish 
and cannot be seen. Before its light can be 
seen it must first be directed to a reflecting 
surface within the body. The light is reflected 
to pass through a considerable lateroventral 
translucent area of lenticular muscles where 
it appears as a diffused bluish glow. This dif- 
fusion may be compared with the effect which 
a frosted or ''opal” bulb of an electric lamp 
has in screening the glare of the incandes- 
cent filament and reducing it to a diffused 
glow. As far as is known this indirect emis- 
sion type is confined to Acropoma and the 
Leiognathidae. 
These fishes differ from other luminous 
fish in possessing unusually large luminous 
areas. In fact they utilize half the muscles of 
their complicated body structure for this pur- 
pose. Recently Kato (1947) discovered that 
Apogon marginatus Doderlein, belonging to 
the family Apogonidae, also possesses this 
same type of luminous organ. 
I have made a study of luminous fishes 
since 1933, and have collected considerable 
material in Japan and in more southerly re- 
gions. Subsequent to 1937 I worked at the 
Palao Tropical Biological Station on several 
occasions during which I took the opportu- 
nity to visit the Philippine Islands, North 
Borneo, New Guinea, Celebes, Java, Suma- 
tra, and Malay, where I collected many spec- 
imens of living luminous tropical fishes and 
observed their luminosity. 
Acknowledgment: I wish to express my 
hearty thanks to Dr. S. Hatai, former Direc- 
tor of the Palao Tropical Biological Station 
and to Dr. Y. Tokugawa, Tokugawa Biolog- 
ical Institute. My thanks are also due to Mr. 
W. Birtwistle, former Director of the Fish- 
eries Department of Singapore and Federated 
Malay States, who helped me in many ways 
during my stay in Singapore. I must express 
my sincere gratitude to Dr. D. J. Pletsch, 
Scientific & Technical Division, ESS, GHQ, 
SCAP, who assisted me in obtaining publica- 
tion of this paper. 
luminescence in Acropoma japonicum 
Material 
Acropoma is a genus of fishes of the family 
