PHOTOSPHERIA OF NYCTIPHANES NORVEGICA. 333 



give out light. Only about oue in four became luminous on 

 being removed from the water. 



Chemical Stimulation. — When an animal was dropped 

 into a saturated solution of bichloride of mercury all the 

 organs shone most brilliantly from five to seven seconds, when 

 the muscles were being violently exerted ; in one case the light 

 lasted for thirty seconds. A similar result followed immersion 

 in nitric acid, -^ per cent., but death ensued more quickly. 

 In both cases the posterior organs ceased to shine first, and the 

 ocular organs were the last to be extinguished. 



One of us spent nearly a whole day in the laboratory 

 examining the fresh organs with the microscope in order to 

 ascertain which part of the photospherion produced the light, 

 and the results of this examination were afterwards verified by 

 both of us. It was found, by repeated trials, that it was occa- 

 sionally possible by crushing the organ under a cover-glass to 

 separate all the component layers from one another. The red 

 pigment was usually dispersed in the operation. All other 

 parts of the organ were seen to be perfectly transparent, 

 including the greater part of the thickness of the reflector, but 

 excepting the internal surface of that layer. That surface in 

 transmitted light glowed with a beautiful luminous-looking, 

 rosy-purple colour, reminding one of a sunset tint. When the 

 light from below was cut off and the preparation viewed by 

 reflected light, the colour was changed to its complementary 

 tint, namely, yellowish-green. The appearance lasted as long 

 as the preparation remained moist, over half an hour, but as 

 time went on the purple colour became more and more tinged 

 with blue, and the complementary colour more distinctly 

 yellow.. The appearance of the most successful preparation is 

 faintly indicated by fig. 7. The most striking fact about the 

 matter was that when the light from the mirror was shut off, 

 and the preparation viewed through a low power, illuminated 

 only by diffused daylight, every part of the preparation was 

 invisible except the coloured surface of the reflector, which 

 appeared to give off a green light in a dark field. But when 

 the daylight was entirely cut off by a cloth coat placed over the 



