APPENDIX. 175 



it, I got a favorable magnifying power, A of Zeiss. With stronger 

 objective there is no good effect. 



" The eye is at first dazzled by a strong, uniform yellowish light. But 

 the intensity of this light is soon checked, the luminous field being inter- 

 rupted by round spots. The light continues to diminish; the image 

 becomes paler ; and between the obscure round spots are seen to appear 

 confused shadows, which detach themselves from the more brilliant rings. 

 These rings are last to disappear when all the other portions have become 

 dark. In the end they disappear entirely. 



" The organ remains dark until the next flash ; only here and there 

 brilliant isolated points persist, which, as we shall see later, represent 

 parenchymal cells which have retained their activity. If one places under 

 the microscope the detached abdomen of a normal Luciola, and excites it 

 by pressure of short duration by the cover glass, it is possible to obtain a 

 flash which resembles the physiological flash." 



M. Emery states that he found it unsatisfactory to examine the insect 

 while alive, as the constant movements rendered it nearly impossible to 

 observe correctly the phenomenon of luminosity. He proceeds : " I have 

 found by poisoning the Luciola by vapors of osmic acid an excellent 

 method in fixing the light, and studying exactly the microscopic aspect. 



" When one examines in a dark chamber the abdomen detached from 

 a Luciola which has been plunged in a solution of osmic acid, it is seen 

 that a part of the segments, occupied by the luminous organs shine with 

 a feeble and variable light ; whilst another part (ordinarily in the neigh- 

 borhood of the median line) is obscure, or as it were veiled by a light 

 phosphorescent cloud. When the preparation is placed under the micro- 

 scope, the luminous parts exhibit towards the top the appearance which 

 we have already noted in examining normal Luciolas ; that is to say, 

 the existence of obscure round spots surrounded by brilliant field. In 

 observing more attentively, one perceives around the spots other little 

 spots, less obscure, and sometimes hardly visible, disposed with a certain 

 degree of regularity. 



" Now, if we compare these images with those which are presented 

 under the microscope by the luminous organs when hardened in alcohol, 

 and cleared up by caustic potash, or else a tangetized section made of 

 the organ of an animal killed by osmic acid, and colored by carmine, it 



