Fig. 141.—Star-gazer (Astroscopus guttatus) settling in the sand. (From life by R. W. Shufeldt.)
Dr. Gilbert has described the electric powers of species of star-gazer (Astroscopus y-græcum and A. zephyreus), the electric cells lying under the naked skin of the top of the head. Electric power is ascribed to a species of cusk (Urophycis regius), but this perhaps needs verification.
Photophores or Luminous Organs.—Many fishes, chiefly of the deep seas, develop organs for producing light. These are known as luminous organs, phosphorescent organs, or photophores. These are independently developed in four entirely unrelated groups of fishes. This difference in origin is accompanied by corresponding difference in structure. The best-known type is found in the Iniomi, including the lantern-fishes and their many relatives. These may have luminous spots, differentiated areas round or oblong which shine star-like in the dark. These are usually symmetrically placed on the sides of the body. They may have also luminous glands or diffuse areas which are luminous, but which do not show the specialized structure of the phosphorescent spots. These glands of similar nature to the spots are mostly on the head or tail. In one genus, Æthoprora, the luminous snout is compared to the headlight of an engine.
Fig. 142.—Headlight Fish, Æthoprora lucida Goode and Bean. Gulf Stream.
Fig. 143.—Corynolophus reinhardti (Lütken), showing luminous bulb (modified after Lütken). Family Ceratiidæ. Deep sea off Greenland.
Entirely different are the photophores in the midshipman or singing-fish (Porichthys), a genus of toad-fishes or Batrachoididæ. This species lives near the shore and the luminous spots are outgrowths from pores of the lateral line.