160 LIVING LIGHTS. 



CHAPTER XX. 



THE USES OF PHOSPHORESCENCE. 



AS to the value and use of the gift of luminosity possessed 

 by various animals, we can only surmise. Many inter- 

 esting theories have been suggested, none of which, however, 

 seem to stand the test of practical application. Some natur- 

 alists believe that the light of certain invertebrates is a 

 warning. As an example, the jelly-fishes have a terrible 

 array of stings ; and it is supposed that fishes once stung, 

 remember the light of these forms, and avoid them in the 

 future. If this were true, many helpless animals, as the 

 salpa and others, would also find protection in the lesson 

 taught by the jelly-fishes. 



It is a poor rule that will not work both ways ; and we 

 might well ask, if nature supplies these lights as warnings, 

 why the physalia, the most terrible of all these forms, has 

 not been thus provided. Phipson mentions it as a phospho- 

 rescent animal, but in the thousands that I have observed 

 during a long residence in the physalia country, I never 

 saw one give out light; hence I assume that if they are 

 luminous, it is only on certain occasions. It might be con- 

 sidered that the vivid colors of this attractive creature 

 constituted a warning; but even this does not hold, as I 

 have found all kinds of pelagic fishes in their toils, and even 



