216 
PACIFIC SCIENCE, VoL IV, July, 1950 
Acropomidae found in the Sea of Japan and 
the Philippine Sea. Two species are known: 
Acropoma japonicum Gunther, and Acropo- 
ma philippinense Gunther. Acropoma phi- 
lippinense was found near the Philippine Is- 
lands by the "Challenger” at a depth of 82 
to 102 fathoms. Acropoma japonicum is 
known as "Hotaru-jako” in Japan, and is con- 
sidered there to be a single species. 
I have examined a large number of these 
"Hotaru-jako” in a fresh condition and be- 
lieve that there are two species (Haneda, 
1939) but in the absence of confirmation of 
this belief by an ichthyologist, I refer to them 
as Type I and Type II ( Figs. 1 and 2 ) . They 
both occur in the southern Japan Sea as a 
mid-water dweller in a depth ranging from 
about 80 fms. to 200 fms. They are beauti- 
fully rose colored and attain a length 200 mm. 
If these two types are examined in detail 
many differences are found, not only between 
their external characters, but also between 
their luminous organs. For example: 
Type I is colored pale red dorsally, and 
whitish ventrally. 
Type II is a beautiful purple-red dorsally, 
and ventrally is light purplish-red. 
Both possess many chromatophores on the 
ventral sides but Type II possesses the 
greater number. 
The scales of Type I are firmly fixed in the 
body, while in Type II they are ex- 
tremely deciduous; for this reason it is 
very difficult to obtain in the public 
fish markets specimens of Type II with 
scales attached. 
The anus in Type I is situated approxi- 
mately under the third spiny ray of the 
dorsal fin, but in Type II it is situated 
below the hindmost edge of the end of 
the dorsal fin. 
The anus in Type I is white and in Type II 
it is strongly black pigmented. 
Type I is furnished with a pair of canine 
teeth which Type II lacks. 
Type I occurs in water of about 80 fms. 
in depth, while Type II occurs in waters 
more than 100 fms. deep. They are 
very seldom taken together by trawling 
vessels. 
The greatest difference, however, lies in 
the size of the U-shaped internal lumi- 
nous gland. That of Type I is short, 
with the ends directed posteriorly; while 
that of Type II is much longer, with the 
free ends directed anteriorly. 
These differences, I suggest, justify the 
creation of a second species, but I prefer to 
call the two kinds of fish Type I and Type II. 
I have examined many specimens of both 
types, as well as males and females of each 
type. The gonads of Type I are full in Octo- 
ber and those of Type II from December to 
February. All ichthyologists have considered 
them to be the same species, A. japonicum- , 
and Type II only a variety of Type I, but in 
my opinion each is a distinct species. 
During the winter season they are caught 
by trawlers in the Gulf of Tosa off Shikoku 
Island, Japan, in depths varying from 80 to 
200 fathoms, and there is no difficulty in 
obtaining specimens in the Mimase fish mar- 
ket near the city of Kochi, Shikoku Island. 
During each of the winters of 1934 to 1940 
I obtained many specimens in this fish mar- 
ket. In Mimase and Urado near Kochi, they 
are called Hotaru-jako, meaning "the small 
firefly fish,” or Kigane-jako, and the fisher- 
men who catch them during the night are 
aware of the luminosity in their ventral re- 
gions, as are most of the ichthyologists, who 
state that the luminosity is due to the numer- 
ous small black points on the ventral sur- 
face of the body. These they consider are 
skin organs similar to those of the luminous 
sharks, but they do not describe their structure. 
It was not until I had dissected many fresh 
specimens that I discovered the peculiar lu- 
minous organs established in them and per- 
ceived that the small black points which had 
