1 82 BIOLOGICAL LECTURES. 



It is, however, possible that some tissues in a non-luminous 

 organism, when thus treated and examined in the dark, may 

 prove to be phosphorescent. 



It is highly desirable that those who have access to various 

 organisms whose photogenic property is suspected from ana- 

 tomical grounds, but not yet definitely proved from the func- 

 tional standpoint, subject such organisms or their suspected 

 tissues to these methods of inquiry. The long-standing con- 

 troversy whether the lantern-fly (Fulgord) is phosphorescent or 

 not, might be settled at once by taking the tissues from the 

 suspected region in the living insect and crushing them. The 

 question whether the eye-like organs in the different parts of 

 the body in bony fishes, Cephalopods, and other organisms, are 

 phosphorescent or not, ought not to be difficult to settle for 

 those who have access to living individuals, or even to dead 

 ones, if the decomposition is not very far advanced ; for the 

 photogenic substance retains the power of phosphorescence 

 long after the death of the organism. 



(c) The third group consists of those in which the definite 

 photogenic organ as such does not exist, but the light-giving 

 material formed by the secretory process of the protoplasm 

 accumulates along the course of muscle-fibres or other contrac- 

 tile protoplasmic material, the light manifesting itself in sparks 

 or scintillations along the course of the fibres at the time of 

 their contraction. This species of phosphorescence is the most 

 interesting one, complicated as it is with the fundamental prop- 

 erty of the protoplasm, namely, contraction. It was this kind 

 of luminous phenomena which retarded the acceptance of the 

 theory that phosphorescence is due primarily to the secretion 

 of a certain material which shines in the process of oxidation. 

 Thus, Alexander Agassiz, 1 in his interesting observations on 

 the phosphorescence of Ctenophores, says : " Although we 

 know now something of the nature of the phosphorescence of 

 a few marine invertebrates from the observations of Panceri, 



part in the process itself. It is probable that water acts as a catalytic agent 

 through which the process of oxidation is accelerated. 



1 Agassiz, Alexander, " Embryology of the Ctenophorae," Mem. Amer. Acad. 

 of Arts and Set., vol. x, No. 3, 1874. 



