THE PHOSPHORESCENCE OF RENILLA. 



By G. H. PARKER. 

 (Read April 24, 1920.) 



The phosphorescence of the sea-pansy Reiiilla has been known 

 for a long time. As early as 1850 Louis Agassiz observed that 

 Renilla renifonnis, the common species of our southern waters, 

 " shines at night with a golden green light of a most wonderful soft- 

 ness." This is also true of Renilla amethystina of southern Cali- 

 fornia. Ha fresh specimen of this species that has been exposed 

 to daylight is carried into a dark-room and stimulated by being 

 gently prodded, no phosphorescence is observable, but if the same 

 experiment is tried at night, the colony glows with a wonderfully 

 clear blue-green light. 



H during daylight non-phosphorescent Renillas are transferred 

 to a dark-room and kept there, they begin to show phosphorescence 

 on stimulation in about half an hour and attain what seems to be 

 their maximum under these circumstances in about an hour. The 

 phosphorescence thus developed seems never to reach the degree of 

 brightness seen during the night. This probably depends upon a 

 natural daily rhythm in the animal's metabolism. Phosphorescence 

 induced during the daytime by placing a colony for an hour or so in 

 the dark is completely lost on exposure to daylight for about five 

 minutes. H during the night a colony that showed a naturally 

 acquired bright phosphorescence is illuminated by strong light, the 

 ability to produce light steadily decreases, but is never entirely lost, 

 showing that either artificial light is not so effective in this respect 

 as daylight or that during the night Renilla is more efificient in pro- 

 ducing the substances necessary for the production of light than 

 during the day. 



Renilla is phosphorescent only on stimulation. H in the night a 

 spot on its upper surface is stimulated mechanically or electrically, 

 luminous ripples emanated from this spot and spread out concen- 



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