THE EYE-LIKE ORGANS OF FISHES. 



169 



These organs have been regarded by many as luminous organs. A 

 single glance shows that the body and lateral walls of the disk shine 

 with a silvery and golden luster, but not different from that of the 

 background of a fish's eye when viewed before a screen. More strik- 

 ing is the appearance in the case of the larger organs of the head in 

 certain species, which are pre-eminently marked by it as a luminous 

 apparatus. But, if the sole object of the apparatus were the collection 

 and reflection of the light which fell upon the fish, its complicated 

 structure in other respects, and its innervation, would be superfluous 

 and still more incapable of explanation. We have, however, an ob- 

 servation that seems to show that these organs not only collect light, 

 but are also really phosphorescent. The distinguished naturalist of 

 the Challenger Expedition, Willemoes-Suhm, now deceased, saw Sco- 

 pelius phosphorescent in the night, of which he says : " One of them 

 hung in the net like a shining star as it came out of the darkness. 

 Possibly the seat of the light is in the peculiar side organs, and it may 

 be that this phosphorescence is the only source of light in the great 

 depths of the sea." The thought that in the dark abysses of the deep 

 sea every animal carries its lantern as the miner carries his lamp on 

 his head, is a very fascinating one ; and, indeed, Herr Willemoes- 

 Suhm observed several other fishes that were provided on the smooth 

 head and on the head-beard with " a remarkably large sense-organ." 

 Valenciennes has also remarked of the genus Hemirarnphus that it 

 bears a strongly glittering phosphorescent pustule on the tip of its tail. 

 Although the majority of these animals have never been observed in 

 a living condition, we might easily agree to the opinion that the or- 



Fig. e.Scqpelus Rafinesquii, twice the natural size. Two luminous orgaus in the ocular region. 



gans of all three categories serve as a more or less perfect illuminating 

 apparatus ; and, if we compare Professor Leydig's sections of them, 

 this opinion, which is only very apparent at the first view, becomes 

 extremely probable. Especially does the section of the eye-like organ 

 of Argyropelecus and Ichthyococcus resemble the illuminating parts of 

 a projection-apparatus. If we conceive the granular spot in the cen- 

 ter, into which the nerves enter, as the source of light standing in the 

 middle of the apparatus, there are likewise behind this the concave 

 reflector, and in front of it the diaphragm through which the con- 

 centrated cone of ray$ is thrown outward under a strong refraction. 



