338 RUPERT VALLENTIN AND J. T. CUNNINGHAM. 



so that light is produced. This is not very clear. In another 

 place he speaks of the secretion produced by glands in the 

 lower part of an organ serving as a fuel, at the expense of 

 which the slender cells above it may produce light. Again, in 

 the case of the simple ocellar organs, he speaks of a special 

 phosphorescent apparatus above, which produces light at the 

 volition of the fish by using up or burning the secretion supplied 

 by the gland, and stored in the space below. 



These views, indefinite as they are, are yet inconsistent with 

 anything that we know concerning animal physiology. It 

 seems to me that they are of the same kind as the ancient 

 notion that the heat of the body was due to the combustion 

 of carbohydrates in the lungs by the oxygen taken in respira- 

 tion. But that the emission of light is really dependent on 

 oxidation in the luminous organs seems to have been con- 

 clusively proved in the case of the glowworm, in which the 

 light was observed to disappear when the animal was placed in 

 a medium destitute of oxygen. Lendenfeld regards the cellular 

 layer at the back of the photospheria in Euphausiidae as com- 

 posed of gland-cells. I cannot see any particular reason for 

 this, as I see no evidence of secretion being produced by them. 

 At the same time it is probable enough that these cells are 

 really the active agents in emitting light, the fluorescent 

 surface of the stratified layer being only an accessory adjunct. 

 All that can at present be said in the way of comparison is 

 that the cells of this cellular layer in the Euphausiidae are similar 

 in general appearance to the cells of the luminous layer in 

 Lampyris splendidula, and that some or other of the cel- 

 lular elements in the luminous organs of fishes are the active 

 light -producing agents. With regard to the refractive globules 

 in the club-shaped cells in fishes, it is possible that these really 

 function as lenses, a number of lenses here perhaps being 

 more advantageous than a single large lens, such as that of 

 Nyctiphanes. 



It is much to be desired that a careful investigation of the 

 production of light in definite organs should be undertaken by 

 a combination of physicists and physiologists, for hitherto the 



