Ch. XXin.] PEOBAELE SOUECE OF LUMINOSITT. 407 



contractility. So also in hi mi nous Annelids, — or perhaps, as 

 better expressed, because the subjects were larger and more 

 highly organised, " in the great majority of cases the light 

 manifests itself in scintillations along the course of the 

 muscles alone, and only during their contraction." The 

 light is entirely unaccompanied by heat, nor is there any- 

 thing analogous to a combustion, either active or slow, of 

 a chemical nature. So also Kolliker, in his examination of 

 the luminous property of the glow-worm (Lampyris), came 

 to the conclusion that there was neither combustion nor 

 phosphorus in the case ; but that it was the product of 

 a nervous apparatus, and dependent upon the will of the 

 animal. 



Ever since, many years ago, I became acquainted with 

 Mr. Grove's researches upon the Correlation of Physical 

 Forces, I have looked upon that ingenious theory as the 

 rational explanation of animal luminosity. Light, heat, 

 electricity, magnetism, motion, and chemical force, are all 

 interchangeable, and each may manifest itself in the form 

 of the other; but although these are called the physical 

 forces, who can say that they are not organic forces also ? 

 One of them, which long since would have been regarded as 

 eminently inorganic, is now fully recognised as an organic 

 force, produced by vital organs, and regulated by the will 

 of the animal exhibiting it. I allude, of course, to electri- 

 city, an agent which is possessed by several fishes, and we 

 know not by what other animals, — a force which is produced 

 directly through the agency of nervous power, for the re- 

 gulation of which a special cerebral lobe is recognised. If 

 this nerve force or vitality can display itself in the form of 

 electricity, why should it not do so also in the form of light? 

 In the more highly organised luminous animals, as in Lam- 



