In one of the anglers (_Corynolophus reinhardti_) the complex bait is said to be luminous, and luminous areas are said to occur on the belly of a very small shark of the deep seas of Japan (_Etmopterus lucifer_). This phenomenon is now the subject of study by one of the numerous pupils of Dr. Mitsukuri. The structures in _Corynolophus_ are practically unknown.
[Illustration: FIG. 144.--_Etmopterus lucifer_ Jordan and Snyder. Misaki, Japan.]
=Photophores in Iniomous Fishes.=--In the _Iniomi_ the luminous organs have been the subject of an elaborate paper by Dr. R. von Lendenfeld (Deep-sea Fishes of the Challenger. Appendix B). These he divides into ocellar organs of regular form or luminous spots, and irregular glandular organs or luminous areas. The ocellar spots may be on the scales of the lateral line or on other definite areas. They may be raised above the surface or sunk below it. They may be simple, with or without black pigment, or they may have within them a reflecting surface. They are best shown in the _Myctophidæ_ and _Stomiatidæ_, but are found in numerous other families in nearly all soft-rayed fishes of the deep sea.
The glandular areas may be placed on the lower jaw, on the barbels, under the gill cover, on the suborbital or preorbital, on the tail, or they may be irregularly scattered. Those about the eye have usually the reflecting membrane.
In all these structures, according to Dr. von Lendenfeld, the whole or part of the organ is glandular. The glandular part is at the base and the other structures are added distally. The primitive organ was a gland which produced luminous slime. To this in the process of specialization greater complexity has been added.
[Illustration: FIG. 145.--_Argyropelecus olfersi_ Cuvier. Gulf Stream.]
The luminous organs of some fishes resemble the supposed original structure of the primitive photophore, though of course these cannot actually represent it. The simplest type of photophore now found is in _Astronesthes_, in the form of irregular glandular luminous patches on the surface of the skin. There is no homology between the luminous organs of any insect and those of any fish.
=Photophores of Porichthys.=--Entirely distinct in their origin are the luminous spots in the midshipman (_Porichthys notatus_), a shore fish of California. These have been described in detail by Dr. Charles Wilson Greene (late of Stanford University, now of the University of Missouri) in the _Journal of Morphology_, xv., p. 667. These are found on various parts of the body in connection with the mucous pores of the lateral lines and about the mucous pores of the head. The skin in _Porichthys_ is naked, and the photophores arise from a modification of its epidermis. Each is spherical, shining white, and consists of four parts--the lens, the gland, the reflector, and the pigment. As to its function Prof. Greene observes: