PHOTOSPHERIA OF NYCTIPHANES NORVEGICA. 335 



glistening sheen. This is doubtless due to the surface of the 

 reflector, and is the same thing as the yellowish-green colour 

 possessed by that surface in a crushed organ in reflected light 

 under the microscope. 



Unfortunately, the observation of the field of the microscope 

 being lit up when a fresh organ was crushed beneath the 

 objective in the dark, was not repeated after the above dis- 

 coveries were made concerning the reflector; and, therefore, 

 we cannot at present say what relation the above-described 

 properties of the reflector have to the emission of flashes of 

 light by the living animal. It is certain that these flashes are 

 more intense than the continuous light given out by the 

 reflector after the organ has been crushed. But the question 

 which demands an answer is this : Is the sudden flash due to 

 a sudden intensification of a phosphorescence always existing 

 in the surface of the reflector? or is the sudden flash produced 

 elsewhere (perhaps in the posterior cellular layer or in the 

 central mass of fibrils), and the fluorescence of the reflector 

 merely a property accessory to its principal function of 

 reflecting the light so produced ? 



In attempting to understand the mechanism of the photo- 

 spheria of the Euphausiidae it is natural to endeavour to get 

 some enlightenment from a comparision between these and 

 luminous organs in other animals. The best known luminous 

 organs are those of the glowworm, and their structure and 

 mechanism have been investigated by Max Schultze 1 and 

 others. Schultze says that researches previous to his own 

 have shown that oxygen is necessary to the emission of light, 

 and that the intensity of light is under the control of the 

 nervous system, while all attempts to isolate phosphorus from 

 the organs have failed. He then proceeds to describe the 

 structure of the organs, which consist of plates composed of 

 two layers of cells. The deeper layer is opaque and non- 

 luminous ; its opacity is due to granules containing uric acid, 

 and probably consisting of urate of ammonia, and the layer 



1 " Leuchtorgaue von Lampyris splendidula," 'Arch. f. mik. Anat./ 

 Bd. i, 1S65. 



VOL. XXVIII, PART 3. NEW SER. A A 



