ied by Günther, Leuckart, Ussow, Leydig, and Emery. Lastly, they have been carefully described by Günther, Moseley, and von Lendenfeld, in the work on "Deep-sea Fishes" in vol. xxvii of the "Challenger Reports." The deep-sea fish are either silvery, pink, or in many cases black, sometimes relieved with scarlet, and, when the luminous organs flash out, must present a very remarkable appearance.
We have still much to learn as to the structure and functions of these organs, but there are cases in which their use can be surmised with some probability. The light is evidently under the will of the fish. It is easy to imagine a Photichthys (Fig. 1) swimming
Fig. l.—Photichthys argenteus ("Challenger Reports," vol. xxvii).
in. the black depths of the ocean, suddenly flashing out light from its luminous organs, and thus bringing into view any prey which may be near; while, if danger is disclosed, the light is again at once extinguished. It may be observed that the largest of these organs is situated just under the eye, so that the fish is actually provided with a bull's-eye lantern. In other cases the light may rather serve as a defense, some having—as, for instance, in the genus Scopelus—a pair of large ones in the tail, so that "a strong ray of light shot forth from the stern-chaser may dazzle and frighten an enemy."[1] In other cases they probably serve as lures. The "sea-devil," or "angler" of our coasts, has on its head three long, very flexible, reddish filaments, while all round its head are fringed appendages, closely resembling fronds of sea-weed. The fish conceals itself at the bottom, in the sand or among sea-weed, and dangles the long filaments in front of its mouth. Other little fishes, taking them for worms, unsuspectingly approach, and themselves fall victims.
Several species of the same family live at great depths, and have very similar habits. A mere red filament would, however, be invisible in the dark, and therefore useless. They have, however, developed (Fig. 2) a luminous organ, a living "glow-lamp," at the end of the filament, which doubtless proves a very effective lure.[2]
These cases, however, though very interesting, throw little light on the use of the muciferous system in ordinary fish, which, I think, still remains an enigma.
