52 
upper eyelid, the base of the pectoral fin, the 
flank, and the ventroposterior corner of the cau- 
dal peduncle. These blackish areas are equipped 
with a greater number of luminous organs than 
are the other portions of the body. The most 
concentrated area of organs is the flank, which 
is dotted with black pigments (Fig. 1), the 
number of organs being 1 1-14 per square mm. 
On the other hand, the luminous organs are most 
sparse on the dorsal region of the body, exclud- 
ing the head. On this area few luminous organs 
could be recognized. 
Of particular interest is the presence of lumi- 
nous organs studded on the ventral surface of 
the upper eyelid (Fig. 2). They are most con- 
spicuous on both the anterior and posterior 
portions of the upper eyelid, but are poorly de- 
veloped or absent at the central portion im- 
mediately above the eyeball. 
Histological Features of the Luminous Organs 
The epidermis of C. ritteri, in which the lumi- 
nous organs are embedded, is composed of a 
stratified squamous epithelium with some mu- 
cous cells. This layer is lined with the stratum 
of dermis which consists of fibroelastic tissues 
(Fig. 3). Throughout the luminous area there 
extends a thin layer of pigment cells between 
the dermis and the epidermis, and the luminous 
organs are usually set on this pigment layer. On 
the scaled area the organs are found to be 
scattered among the placoid scales. Most of 
the luminous organs are obliquely situated and 
slightly inserted in the distal portion of the 
dermis. 
Each luminous organ is a hemispherical cup 
in shape, and is composed of four main ele- 
PACIFIC SCIENCE, Vol. XIV, January I960 
ments, (1) photogenic cells, (2) an irislike 
structure of pigment cells, (3) lens cells, and 
(4) a pigment sheath covering the organ. 
The photogenic cells, approximately 7-12 in 
number, occupy the bottom of the organ. These 
cells are of a glandular type with an eosinophil 
secretion in their distal portion. Photogenesis 
seems to be intracellular. The lower half of a 
mass of photogenic cells is covered directly with 
the pigment sheath without a reflectorlike struc- 
ture (Fig. 3). 
Along the peripheral border of the mass of 
photogenic cells, there is a crowding of the pig- 
ment cells (Fig. 3). These are arranged in a 
circle and send out dendritic inward projections 
covering the cup. They apparently are capable 
of controlling themselves in the area which in- 
tercepts the photogenic body. This structure, 
therefore, may serve as an iris to regulate the 
amount of the light emitted from the photogenic 
cells. The arrangement of pigment cells of this 
structure resembles that of Etmopterus fronti- 
maculatus rather than E. lucifer, described by 
Ohshima (1911: 4). The irislike structure of 
the latter species is more developed, that is, the 
pigment cells extend further toward the lens 
cells (Fig. 4). 
Each luminous organ bears two or three lens 
cells lying above the cup. These cells are peculiar 
in containing a large amount of homogeneous 
concretion stained with orange G in cytoplasm, 
though some are vacuolated. This fine structure 
perhaps acts as a lens to concentrate the light 
emitted from the photogenic body. The nucleus, 
ovoid in shape, lies near the base of the cells. 
Because of the lack of young material, it was 
caudal peduncle in which luminous organs are densely distributed. Scale bar indicates 10 mm. 
