174 PARKER— PHOSPHORESCENCE OF RENILLA. 



material already alluded to can on stimulation be made to glow. 

 Thus right or left halves, quadrants, centers, margins or even minute 

 fragment will on appropriate treatment give out light. 



The impulses that induce phosphorescence are profoundly in- 

 fluenced by such anesthetics as magnesium sulphate. If a prepara- 

 tion is made by cutting a disc of Renilla almost in two by a trans- 

 verse incision and, after determining that the connecting bridge will 

 transmit luminous waves, this bridge is covered with crystals of 

 magnesium sulphate, the waves of light in ten minutes or so will be 

 blocked at the bridge and light will be produced in only that part 

 of the disc which is directly stimulated. After half an hour or so 

 in pure seawater the bridge will again transmit the luminous waves. 



If a V-shaped preparation is made from a Renilla by splitting it 

 through its long axis except at the distal end of the peduncle, it will 

 be found, as already stated, to transmit impulses for light produc- 

 tion from one half to the other through the partly split peduncle. 

 If the unsplit portion of the peduncle is now covered with crystals 

 of magnesium sulphate, in five to ten minutes no impulses to illumi- 

 nation will pass through it, for when one half is excited to glow the 

 other does not follow by producing a flash. Recovery from this 

 condition occurs after the preparation has been for half an hour or 

 so in pure seawater. 



The rate at which the luminous waves traverse the disc of 

 Renilla is a relatively slow one. To determine it, strips of tissues 

 were cut from the edge of the disc and pinned out in seawater. 

 They measured five to eight millimeters in width and about ten 

 centimeters in length. After night had come on these strips could 

 be stimulated by touching one end gently with a metal rod where- 

 upon a single wave of light would pass rapidly over the length of 

 the strip. This could be timed by a stop-watch. Five such prepara- 

 tions were tested with the result that the average rate of transmis- 

 sion was found to be 7.39 centimeters per second. This rate agrees 

 almost exactly with that for the withdrawal of the zooids in Renilla, 

 namely 7.83 centimeters per second and indicates that both these 

 processes are controlled by a single mechanism. As these rates are 

 close to that of the nerve-net of the sea-anemone Metridium, namely, 

 12 to 14 centimeters per second, the common mechanism upon which 



