220 
PACIFIC SCIENCE, Vol. IV, July, 1950 
Acropoma japonicum are peculiar organs of 
a new type. The luminous glands are situ- 
ated in the muscles, and they may be con- 
sidered as an indirect or reflecting type of lu- 
minous organ functioning by reflected light. 
Remarks on the Luminescence 
Since the luminous gland is not visible on 
the surface of the body, both types of fish, 
externally and in daylight, have the appear- 
ance of ordinary non- luminous fish. 
In the dark, however, e.g., when caught 
alive in a net at night, the ventral area is 
brilliantly illuminated. The luminosity is con- 
tinuous, never disappearing completely, but 
may be dimmed by means of the chroma- 
tophores. 
When the fish are recently dead the lumi- 
nosity persists in both types, but gradually 
becomes dim. One or two days after death 
the muscles become opaque and are no longer 
translucent, and then the luminosity is ex- 
tremely dim. If, however, after this period, 
the luminous glands are removed it will be 
seen that their luminosity persists as brilli- 
antly as before and can even be seen in 
daylight by shading the glands in the cupped 
hands. 
Remarks on the Substance 
in the Luminous Glands 
To examine the substance in the glands, I 
made emulsions of it in distilled water, in 
0.5, 2, 3, and 4 per cent NaCl solutions, and 
in sea water. These emulsions were kept at 
18°-23° C. and were examined in the dark. 
The sea water emulsion was the most lu- 
minous; next in order were the 3 per cent 
NaCl, the 4 per cent NaCl, the 2 per cent 
NaCl (which was rather weak), and the 
0.5 per cent NaCl (which was extremely 
weak ) . The distilled water emulsion was not 
luminous. 
The temperature of the sea water emulsion 
was lowered to 0° C, at which temperature 
it showed only a weak luminescence, but re- 
covered its strength when warmed to 18° to 
23° C, within which range it was strongest. 
At temperatures above 30° C. the luminosity 
diminished until at 45° C. it was no longer 
visible. When cooled it regained its lumi- 
nescence, but it was lost again below 0° C.; 
however, luminescence was again recovered 
when the emulsion was warmed. 
The Luminous Bacteria 
When the emulsion of the gland was ex- 
FlG. 3. Acropoma japonicum Gunther Type 1 The luminous organ is not seen externally, so that 
the fish looks like a common non-luminous one, but the lower part of the fish body is a lightning-like 
bluish-white color. 
