PROBLEMATICAL ORGANS OF SENSE. 103 



ied by Giinther, Leuckart, Ussow, Leydig, and Emery. Lastly, 

 tliey have been carefully described by Giinther, Moseley, and von 

 Lendenf eld, 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 sur- 

 mised 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.—PtMtichthys argenteus (" Challenger Report?," 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." * 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 con- 

 ceals itself at the bottom, in the sand or among sea-weed, and dan- 

 gles 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.f 



These cases, however, though very interesting, throw little 

 light on the use of the mucif erous system in ordinary fish, which, 

 I think, still remains an enigma. 



* Giinther (" Challenger Reports," vol. xxvii). -f Giinther, " Study of Fishes." 



