430 PHYSIOLOGICAL LIGHT. 



A confirmation of the accuracy of this theory, which I consider as 

 final, has been furnished by my recent researches upon luminous 

 myriapods. 1 



The Orya barbarica of Algeria, which we have mentioned in the first 

 part of this article, secretes by special hypodermic unicellular glands a 

 luminous liquid free from foreign m after. The microscope readily reveals 

 not only in the glandular protoplasm, but also in the secreted product, 

 the vacuolides or photogenic granulations, which can be seen to become 

 transformed into magnificent crystals during the emission of light. 

 When the phenomenon is completed the preparation is composed 

 wholly of crystals. The photogenic matter rapidly dried (on filter 

 paper, for example) may remain in a colloidal state for a long time and 

 become reillumined by a drop of water when exposed to air. In the 

 particular case of Orya barbarica, one could not apply the hypothesis of 

 Eadziszewski, that the luminosity is occasioned by a pure and simple 

 oxidation of certain organic substances in an alkaline medium at an 

 ordinary temperature, for the secretion of Orya is clearly acid. Besides, 

 all the reactions indicated for Pholas are applicable to the luminous 

 secretion of this Algerian myriapod. 



III. 



From all these observations and experiments, the following conclu- 

 sions may be drawn : 



First. The photogenic phenomenon requires for its accomxfiishment 

 neither the integrity of the organ nor of the cellular elements; the 

 activity of the cell alone, when it is not independent, assures the activ- 

 ity of the organ. The cell, in its turn, forms the photogenic substance; 

 but that, when once formed, may shine or become extinguished inde- 

 pendently of the anatomical element that produced it, according to 

 circumstances affecting its environment. 



Second. The environment must be such as to satisfy the conditions 

 indispensable for the production of the phenomena of life; it should 

 contain water, be oxygenated, and have a suitable temperature. 



Third. All the causes that suspend or abolish the activity of zymoses 

 or figurate ferments, or, to speak more generally, protoplasmic activity, 

 also suspend or abolish the photogenic function — that is to say, the 

 production of physiological light. 



Fourth. It is in passing, by reason of an inevitable ancestral impul- 

 sion, from the state of living protoplasmic granulations to the state of 

 crude crystalloid matter that the photogenic substance disengages at 

 one and the same time, under the form of light, the evolutive energy 

 received from its ancestors and the compensatory energy drawn from 

 its environment. 



J See Comptes reudus do 1'Acaderuie dps Sciences, 17 juillet, 1893. 



