Luminous Organs of Fish — HANEDA 
21s) 
C 
Fig. 2. Diagrammatic figure of the luminous organ of Acropoma japonicum Type II: phot, lumi- 
nous gland; lens, lens; refl, reflector; a’, b’, c’, d’, e’ — transverse sections at a, b, c, d, and e. 
made if the closed end of a hairpin were bent 
over to form a hook. 
The free ends of each limb of this organ 
lie in the isthmus, and the arrangement is a 
complete reversal of that found in Type I. 
The gland is reddish-yellow when fresh. 
Structurally it is similar to that described for 
the fish of Type I. 
The central canal between the inner loops 
continues beyond the anus and opens into 
the cloaca through an opening which com- 
pletely encircles it. 
The muscles which form the lenses are 
comparatively poor as lenses when compared 
with those of the Type I fish, but are similar 
in other respects and equally translucent. The 
chromatophores are extremely numerous in 
the ventral region, and there are many more 
of them than in the fish of Type I. 
These two types of luminous organs of 
