66 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 
Fic. 50—Section of the deeper portion of phosphorescent organ of Porichthys 
notatus, highly magnified. (After Greene.) 
stinlight, 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- 
