ON LUMINOUS ORGANS OF FISHES. ö 



broader, its caudal prolongations on both sides of tlie tail fin {C[) 

 longer, and the solitary areas on the tail fin ( C2} shorter than 

 in lucifer. 



In both species the punctate photophores are densely clus- 

 tered in the following parts : small areas surrounding the nostrils, 

 the ventral margin of the orbit, bases of paired fins, and lastly 

 the postanal and caudal areas with their extensions. In these 

 areas there are to be counted as many as sixty or seventy 

 photophores in a square mm. of the skin, while in most other 

 parts their number in an equal area does not exceed thirty 

 or forty, and in still other parts where they are most scattered, 

 it sinks to ten or thereabout. 



External JPeatuves. 



In spirit or formalin specimens, the photophores are seen 

 as minute *' nicht glänzende Punkte " on the dark skin. But 

 this is not the case in the fresh state, when they appear as 

 spots of a pearly lustre and their distribution can be made 

 out with the naked eye without much difficulty. Under a low 

 magnification, each organ is seen to be composed of a number of 

 polygonal elements of a pearly lustre cUistered together to form 

 a rounded area and surrounded by a black ring of thickly 

 accumulated pigment. The pearly lustre vanishes in preser- 

 vative media. 



The following table shows the dimensions of the organs 

 measured in preparations mounted in iolo : — 



