LIGHT-ORGANS. 185 



of, and in relation to, the muciferous systeQi ; while in 

 others they are variously situated. These luminous 

 organs were first mentioned by Cocco.* They have 

 since been studied by Giinther, Leuckart, Ussow, 

 Leydig, and Emery. Lastly, they have been carefully 

 described by Giinther, Moseley, and von Lendenfeld 

 in the work on "Deep-Sea Fishes," in. vol. xxvii. of 

 the "Challenger Keports." 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. 114), swimming 



Fig. IH.— 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 



* Niiovl Ann. dei Sci. Nat, 1838. 



