Fishes Photoblepharon and Anomalops. 47 



of the two fish are different, Photoblepharon being stouter in pro- 

 portion to the length. Sometimes the former grows to large size and is 

 caught by hook and line. Mr. Baadilla, of Banda Neira, told me of one 

 about 250 mm. long. The usual size for Anomalops is 102 mm. from 

 head to base of tail, 32 mm. high, and 28 mm. thick at the gills. Its 

 luminous organ will measure 12.3 by 5.7 by 1.4 mm. and weigh 

 about 0.08 gram. In Anomalops the two luminous organs together 

 make up about 0.58 per cent of the body-weight. This is not as 

 large a proportion as we might expect when we consider that the 

 organ looks very large and is actually one-eighth to one-tenth the 

 length of the fish itself. No doubt the eggs which filled the abdomen 

 of the Anomalops examined greatly reduced the weight proportion 

 of luminous organ to whole fish, that would be observed in a fish 

 without eggs. 



In both fishes the luminous organ is a compact mass of white to 

 cream-colored tissue, flattened oval in shape, lying in a depression 

 just under the eye and in front of the gills. The organ looks as if 

 made for experimentation, as it is attached only at the dorso-anterior 

 end and can be cut out with the greatest ease, giving a piece of prac- 

 tically pure luminous tissue. The back of the organ is covered with 

 a layer of black pigment which serves to keep the light from shining 

 into the tissues of the fish. In both fish there is a mechanism for 

 obscuring the light, but curiously enough the mechanism developed 

 is totally different in the two species, notwithstanding the fact that 

 in structure the organ is identical in the two and in every detail 

 except proportion the fish are very similar. 



In Ariomalops, the organ is hinged at the antero-dorsal edge and 

 can be turned downward until the light surface comes in contact 

 with a fold of black-pigmented tissue forming a sort of pocket. The 

 light is thus cut off. In Photoblepharon, a fold of black tissue has 

 been developed on the ventral edge of the organ socket, which can 

 be drawn up over the fight surface like an eyelid, thus extinguishing the 

 light. Why these two fish, so similar in most respects, and especially in 

 the general structure of the luminous organ, should have developed such 

 totally different means of extinguishing the light is a mystery. 



As observed by Steche, I find that the organ itself emits light 

 continuously and steadily, in the day as well as at night. No 

 amount of mechanical or electrical (strong interrupted induced 

 shocks) stimulation causes any effect whatever on the intensity. In 

 this respect it differs completely from all other animals and resembles 

 the bacteria and fungi, which also produce a steady light independent 

 of stimulation. One other fish, Monocentris japonica, with a paired 

 light-organ at the tip of the lower jaw, behaves as do Anomalops and 

 Photoblepharon. This peculiarity of steady light, independent of 

 stimulation, should be borne in mind, as it has a very important 

 bearing on the nature of the light of these fishes. 



