LIGHT-ORGANS. 185 



of, and in relation fo, the muciferous system ; wliile in 

 others tliey are variously situated. These luminous 

 organs were first mentioned by Cooco.* They have 

 since been studied by Giinther, Leuckart, Ussow, 

 Leydig, and Emery. Lastly, they have been caiefuUy 

 described by Giinther, Moseley, and von Lendenleld 

 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 cai-es black, sometimes 

 relieved with t^carlet, and, when the luminous organs 

 flash out, must present a very- remarkable app' arance. 

 We have still much to learn as to the structure and 

 i'uiictions of these organs, but there aie 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 Photichthy.s (Fig. 114), swimming 



Fig. lli.—Photichthys argenteus (" Cballeoger Eeports," 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 



* Nuovi Ann. dei Sci. Nut, 1838. 



