i 9 4 



Adaptations of Fishes 



ever, not numerous enough to more than suggest the possibility 

 of a seasonal high development of the phosphorescent organs. 



" Two of the most important parts of the organ have to do 

 with the physical manipulation of light the reflector and the 

 lens, respectively. The property of the reflector needs no dis- 

 cussion other than to call attention to its enormous develop- 

 ment. The lens cells are composed of a highly refractive sub- 

 stance, and the part as a whole gives every evidence of light 

 refraction and condensation. The form of the lens gives a 

 theoretical condensation of light at a very short focus. That 

 such is in reality the case, I have proved conclusively by exami- 

 nation of fresh material. If the fresh fish be exposed to direct 



FIG. 148. Section of the deeper portion of phosphorescent organ of Porichthys 

 notatus, highly magnified. (After Greene.) 



sunlight, there is a reflected spot of intense light from each 

 phosphorescent organ. This spot is constant in position with 

 reference to the sun in whatever position the fish be turned 

 and is lost if the lens be dissected away and only the reflector 

 left. With needles and a simple microscope it is comparatively 

 easy to free the lens from the surrounding tissue and to examine 

 it directly. When thus freed and examined in normal saline, I 

 have found by rough estimates that it condenses sunlight to a 

 bright point a distance back of the lens of from one-fourth to 

 one-half its diameter. I regret that I have been unable to make 

 precise physical developments. 



" The literature on the histological structure of known phos- 

 phorescent -organs of fishes is rather meager and unsatisfactory. 

 Von Lendenfeld describes twelve classes of phosphorescent 

 organs from deep-sea fishes collected by the Challenger expe- 



