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: "I have kept specimens of _Porichthys_ in aquaria at the Hopkins Seaside Laboratory, and have made numerous observations on them with an effort to secure ocular proof of the phosphorescence of the living active fish. The fish was observed in the dark when quiet and when violently excited, but, with a single exception, only negative results were obtained. Once a phosphorescent glow of scarcely perceptible intensity was observed when the fish was pressed against the side of the aquarium. Then, this is a shore fish and quite common, and one might suppose that so striking a phenomenon as it would present if these organs were phosphorescent in a small degree would be observed by ichthyologists in the field, or by fishermen, but diligent inquiry reveals no such evidence.