Luminous Organs of Fish — HANEDA 
217 
been believed to be small luminous organs 
were nothing more than chromatophores. 
The luminous organs consist of the fol- 
lowing five components: a U-shaped lumi- 
nous filiform body; an external opening of 
the canal of the luminous body; a reflector; 
a series of lenses; and a means of controlling 
the display of luminescence. 
Luminous Organ of A. japonicum Type I 
(Fig. 1) 
Luminous Gland — -The luminous gland is 
a whitish-yellow U-shaped filiform body, like 
a U-tube, lying flat and embedded in the mus- 
cles of the pectoral and ventral regions. Each 
"limb” of the tube is sealed at its end. The 
bend of the tube lies nearer the head than 
the closed ends of the "limbs” or filaments. 
This bent filament has an outer layer of lon- 
gitudinally arranged fibers, an inner layer of 
circularly arranged fibers, and an innermost 
folded glandular epithelium, which surrounds 
a hollow duct or cavity. It is pierced on the 
Fig. 1 . Diagrammatic figure of the luminous organ of Acropoma japonicum Type I: phot, lumi- 
nous gland; lens, lens; refl, reflector; a’, b’, c’, d’, e’, f — transverse sections at a, b, c, d, e, and f. 
