Luminous Fishes — Haneda 
15 
scribe it simply as a mass of gelatinous sub- 
stance without commenting on its shape. 
However, if fresh material is examined, the 
surface of the so-called simple mass of gelatin 
is convex, the body is swollen, and it 'has a 
definite shape. The only person to suggest 
that it might be a lens is Mangold (1910). 
It is probable that most investigators have 
worked on preserved and dead material, and 
this may account for their failure to recognize 
it as a lens and to misunderstand its function. 
If the organ is put into alcohol or formalin, it 
contracts and becomes cloudy and shapeless, 
the sides shrink and become concave, and the 
coloring matter in the filter disappears. It is 
difficult to recognize the real function of the 
organ after such treatment. 
Pigmented Membrane 
This membrane covers the outside of the 
reflector. One of its functions is to assist the 
reflector, and another is to prevent light from 
being dissipated by entering the surrounding 
body muscle in which the organ lies. 
Sometimes, the normally separate luminous 
organs are joined together to form a single 
luminous organ in the ventrothoracic region. 
Fine blood vessels enter through the reflector, 
ramifying in all directions within the lumin- 
ous body and the filter. Nerves are also said to 
do the same, but I have not investigated this 
statement. 
Unlike the Leiognathidae and other sym- 
biotic luminous fishes which are able to con- 
trol their display of luminescence by means of 
'their chromatophores, Polyipnus and Yarrella 
are not provided with such structures. Never- 
theless they can control it, but how they do 
so I am unable to say. Perhaps they are able 
to do it by means of their blood vessels or 
nerves. 
These luminous organs are the closed type 
without any external openings and are unlike 
the open type possessed by the Gadidae 
(Kishitani, 1930), Macrouridae (Haneda, 
1938), Monocentridae (Yasaki, 1928), Acro- 
pomatidae (Yasaki and Haneda, 1936), and 
Leiognathidae (Haneda, 1940), which possess 
external openings and are luminous by virtue 
of the luminous symbiotic bacteria within 
their open luminous organs. 
I have been unable to find any bacteria, 
either luminous or non-luminous, in the 
organs of the Yarrella and Polyipnus fishes 
under discussion, in spite of an extensive 
search for them by the usual bacteriological 
methods. Luminous fishes with the closed 
type of luminous organs are true luminous 
fishes, and the luminosity which they display 
is the result of some product of the fishes’ 
own creation and not the product of sym- 
biotic bacteria living in the duct of the lumin- 
ous organ of the fish. 
ACKNOWLEDGMENTS 
I wish to express my sincere gratitude to 
Dr. D. J. Pletsch, Scientific and Technical 
Division, ESS, GHQ, SCAP, who helped me 
to obtain publication of this paper. 
REFERENCES 
Haneda, Y. 1938. Ueber den Leuchtfisch, 
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thidae of the tropical Pacific. Palao Prop. 
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Kishitani, T. 1930. Studien fiber die Leucht- 
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Mangold, E. 1910-14. Die Produktion von 
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