The Chemistry of Light-Production in Luminous Organisms. 223 



The light of the skin-organs scattered over the ventral surface lasts 

 much longer, and even after removal from the sea-water for 1 hour 

 they will give a light which is more yellowish if stimulated electrically. 

 The response is localized in the region about the electrodes. 



The eye-organs are difficult to stimulate. Their light is weak and 

 similar to that of the skin-organs. 



The squid are caught at night in enormous numbers during April, 

 May, and June by the fishermen, and Professor C. Ishikawa informs me 

 that if brought into a dark room in the daytime they give light. The 

 squid for this experiment were caught at 3 a. m. and tested about 

 8 a. m. — i. e., 3 or 4 hours after daylight had appeared. There is no 

 inhibiting influence of daylight on light-production, as described by 

 Peters (4) for Ctenophores or Moore (5) for various luminous plankton 

 forms. Neither have I observed any such influence of light with 

 Monocentris, Cypridina, Cavernularia, Pennatula, or Noctiluca. 



PHOTOGENIN AND PHOTOPHELEIN. 



An extract presumably containing Watasenia photogenin can be pre- 

 pared in the usual way by grinding the arm-tip light-organs in a mortar. 

 As already mentioned, the light fades very rapidly, and it is impossible 

 to again obtain light by mixture with the boiled-tissue extract of the 

 squid (or with tissues heated to temperatures below boiling), which 

 presumably should contain photopheleih. Many attempts were made 

 to obtain the photogenin-photophelein reaction, but all failed. This 

 result is probably due to the fact that Watasenia contains more photo- 

 phelein than photogenin, so that all the photogenin is used up when 

 the arm-tip organs are ground. At least, Watasenia contains photo- 

 phelein which will give light with firefly photogenin, whereas the firefly 

 photophelein will give no light with Watasenia extracts which we might 

 suppose to contain photogenin (p. 198). 



STUDIES ON A FISH. MONOCENTRIS JAPONICA. 



Monocentris japonica is a shallow-water marine fish having two 

 light-organs — one on each side of the under surface of the tip of the 

 lower jaw. The light is a weak glow w^ith the faintest bluish tinge and 

 is continuous and of almost unvarying intensity. In this respect it 

 differs from most fishes, whose light is a series of flashes, the result of 

 stimulation (Oshima, 33). The steady glow of the organs of Mono- 

 centris can be observed if the fish is removed from dayUght to a dark 

 room. The structure of the organ has never been investigated. 



If the organ is ground in a mortar, the light lasts for some time, but 

 does not reappear if mixed with Monocentris photophelein. Neither 

 was light obtained by mixing Monocentris photogenin and Cypridina 

 photophelein or vice versa, but as material was scarce, only one experi- 

 ment was performed, and these results must not be considered con- 

 clusive. 



