ON LUMINOUS ORGANS OF FISHES. 9 



cells''' which form what I have called the '' iris." When con- 

 tracted, they allow the exit of the light produced in the pho- 

 togenic body lying underneath, while their expansion makes the 

 iris act as a screen that shut in the light. 



If it be, as Johann has made out in Spinax niger, that 

 the organ is not specially innervated, this may be in relation 

 with the fact that mechanical stimulation does not cause im- 

 mediate change of the luminescent phenomena. 



II. Luminous Organs of Sternoptychidae. 



As a representative of the family Sternoptychidae, I have 

 taken Matirolicus pennanti (Walbaum) for the study of the 

 luminous organ. 



Topograph ical Distr Unit ion. 



Gatti is entirely right in his description of the distribu- 

 tion of the organs, the number of photophores as given by him 

 exactly coinciding with that of my specimens, while those given 

 by Ussow, Jordan and Evermann and recently by Mangold 

 differ from mine. 



Edcternal Features» 



The luminous organs, wdien viewed from the ventral side, 

 are of a beautiful amethyst colour in the fresh state, with a 

 slightly convex surface. Mangold is of the opinion that the 

 colour is a " Strukturfarbe " or an interference colour caused by 

 a special arrangement of the spicules forming the reflector, but 

 my observations have led me to a different conclusion. 



* Prof. Watasé has expressed a similar opinion on the lumhious organs of Abraliopsls. 



