PHOTOSPHERIA OF NYCTIPHANES NORVEGICA. 339 



most profound physical and physiological knowledge has not 

 been applied to the problem. We content ourselves, in the 

 above pages, with having worked but the internal structure of 

 the organs of Nyctiphanes in detail, and having called atten- 

 tion to the interesting physical properties of the surface of the 

 stratified layer. 



P.S. — In the above brief review of researches on the phos- 

 phorescence of other animals than Euphausiidae we have 

 omitted to refer to the important papers of Panceri. The 

 principal of these are memoirs published by the Academy of 

 Naples, namely, on the phosphorescence of the Peunatulidae, 

 1871, on that of Pyrosoma and Pholas, and on that of Phylir- 

 rhse, 1872. Besides these there are valuable abstracts in the 

 1 Comptes Rendus of the Acad. Roy. de Naples/ of the years 

 1871 and 1872. These abstracts are to be found in a French 

 translation in the ' Ann d. Sci. Nat./ tome xvi, 1872, and it is 

 to this source that we owe our knowledge of Panceri's views. 



The production of light in all the cases investigated by him 

 is, according to Panceri, exclusively due to a special granular 

 substance having apparently the nature and properties of a fat. 

 He found a species offish, Trachypterus iris, to be luminous 

 in all parts ; light emanated from almost the whole external sur- 

 face, from the muscles when they wereexposed, and from the viscera 

 shortly after the abdominal cavity was opened. The liquid which 

 drained from the flesh was luminous and gave that quality to 

 every surface which it covered. This liquid was merely the oil 

 of the animal, and the light was due to oxygen, being extin- 

 guished by carbonic acid and intensified by oxygen, not imme- 

 diately but after an exposure of some hours. 



In Medusas Panceri found that the property of luminosity was 

 confined to the epithelium either of the external or of internal 

 surfaces, and was due to a substance contained in the cells of 

 the epithelium, which substance resembled fat. 



In Pennatula there are on each zooid eight cords or ridges 

 on the external surface of the stomach. These ridges are com- 

 posed principally of a substance of a fatty nature contained in 



