172 PARKER— PHOSPHORESCENCE OF RENILLA. 



trically over its surface like waves on the smooth face of a pond into 

 which a pebble has been thrown. If a fine needle point is used as 

 a stimulus, a single point of light can be excited and this point will 

 glow some seconds but without becoming a center from which 

 luminous waves spread. 



When a glowing Renilla is examined under a hand lens, the parts 

 from which the light emanates are seen to be small masses of light- 

 colored material that stud the upper surface of the animal and that 

 surround the bases of the zooids. Apparently light emanates from 

 no other source. No phosphorescence has ever been excited from 

 the peduncle by which the animal anchors itself in the sand, nor 

 from the under surface of the disc. The phosphorescence is strictly 

 limited to the upper surface and apparently to the light-colored 

 material of that surface. If a bit of this material is cut from the 

 disc at night-time and carried into a dark room and crushed between 

 glass, a momentary sparkling can be seen. If this experiment is 

 tried with a bit of the purple flesh of the upper surface, no such 

 sparkling is produced. Hence it is clear that the source, of the 

 phosphorescence is the light-colored material of the upper surface 

 of the disc. 



This light-colored material on close inspection is seen to be com- 

 posed of two substances : a whitish chalky substance and a light- 

 yellowish crystalline one. These two substances are so intimately 

 associated that it is impossible to separate them satisfactorily or in 

 most places to determine by direct inspection which is responsible 

 for the light. Only on the edge of the disc is it possible to make 

 decisive observations. Here the two substances form a well-marked 

 double fringe, the outer one being composed exclusively of the white 

 material, the inner one of the yellowish. When phosphorescence is 

 excited on the adge of the disc, it can be seen that the light is resi- 

 dent in the white fringe and not in the yellow and hence the former 

 material must be regarded as the true source of the phosphorescence. 

 When this material in a luminous state is inspected under a hand 

 lens it is indescribably beautiful; the light it gives out is of an in- 

 tense blue-green color with all the play that one sees in a brightly 

 illuminated opal. 



The mechanical or electrical stimulation of Renilla at night re- 



