Squaloid Shark— IwAl 
53 
FIG. 2. Diagrammatic aspect of cross section 
through the eye, showing the supraorbital luminous 
area (la). Scale bar indicates 5 mm. 
impossible to trace a sequence of development 
of the lens cells. The staining reaction of the 
lens cells in this species is quite dull as com- 
pared with that of E. lucifer (cf. Figs. 3, 4). 
This may be due to a poor condition of fixation. 
The proximal border of the luminous organ 
is lined with the cup-shaped pigment sheath 
(Fig. 3), which may prevent the diffusion of 
light to the lining stratum. It continues to the 
iris at the distal end. 
There is no reflectorlike structure at the base 
of the photogenic body, whereas highly de- 
veloped luminous organs of teleostean fishes are 
usually provided with a well-developed reflector. 
The histological examinations mentioned 
above show that the luminous organs of C. rit- 
teri are not as well developed as those of E. 
lucifer, either in number or in structure. But as 
far as the structural evidence is concerned, it 
is not unreasonable to assume that these organs 
may be functional. 
DISCUSSION 
In the absence of living material, there is 
doubt as to whether or not the luminous organ 
of this shark is functional. Ohshima (1911: 7) 
and Schmidt ( 1931: 9), both working with liv- 
ing Etmopterus frontimaculatus , observed that 
feeble luminosity appears throughout the ven- 
tral surface and that the light is not produced 
spontaneously but is emitted regularly by me- 
chanical stimulation. The fact that the location 
and structure of the organs of C. ritteri are vir- 
tually the same as those of Etmopterus may 
imply that the present deep-sea shark is lumi- 
nous. In his work on the luminous organs of 
elasmobranch fishes, Burckhardt (1900: 567- 
568) found luminous organs in both Centro- 
scyllium granulatum and C. fahricii. Bigelow and 
Schroeder (1957: 38) also suggested the pos- 
sibility of luminescence with thickenings of the 
black skin in some species of Centroscy Ilium. 
These data would lead one to suppose that all 
the members of Centroscyllium possess luminous 
organs, as is the case with the genus Etmopterus . 
In several groups of fishes the characters of 
the luminous organs have been adequately dis- 
cussed and appear to offer good evidence for 
separating the species. Haneda (1950: 216) 
and Matsubara (1953: 21) recognized two 
distinct species of the genus Acropoma based 
chiefly upon the form of the luminous organ, 
though the latter author added further features 
which enable us to distinguish the species. Iwai 
and Asano (1958: 8), upon studying the struc- 
ture of the luminous organs as well as other 
FIG. 3. Transverse section through a luminous or- 
gan on the flank of C. ritteri. (X ca - 350). i, Iris; 
1c, lens cell; pc, photogenic cell; ps, pigment sheath. 
