ORGANIZATION OF RENILLA 505 



The phosphorescence of Renilla is limited to the superior sur- 

 face of the rachis, and when this surface is scrutinized closely 

 under a hand lens, it is found that the phosphorescence is not 

 a property of the whole surface, but appears only in certain al- 

 most microscopic white granulations. These occur around the 

 openings in the common flesh through which the autozooids 

 emerge and particularly on the siphonozooids. When these 

 small white granules are touched with a fine needle-point, they 

 can be seen to shine for a considerable time with a bright blue- 

 green light. This individual activity is easily excited, but it 

 is not the characteristic form of luminous response. If an area 

 on the superior surface of the rachis is vigorously stimulated 

 mechanically or by a faradic current, waves of phosphorescence 

 sweep from this area as a center over the whole of the superior 

 face of the rachis. These waves succeed one another at such a 

 rapid rate that the whole superior surface seems to be covered 

 with a rippling glow emanating from the region of stimulation. 

 After the application of the stimulus the luminous response 

 quickly subsides. 



The general luminosity just described may be excited from 

 any point on the superior surface of the rachis. When the edge 

 of the rachis is stimulated, waves semicircular in form emanate 

 in rapid succession from the stimulated spot. When a central 

 position is chosen for stimulation, the waves pass out as ever 

 enlarging circles concentric about the point stimulated. A close 

 scrutiny of each wave shows that it is not due to a general phos- 

 phorescence of the whole surface, but is the result of successive 

 glowings of the white granulations already mentioned. It is 

 difficult to understand how these successive activities are induced 

 unless it is assumed that the luminous points are all controlled 

 by a nerve-net whose form of transmission is reflected in the 

 outward moving circles of light. Since individual granules may 

 be made to glow brightly and persistently, it is plain that the 

 light of one granule does not automatically excite the next and 

 so on thus resulting in a wave of luminosity. The whole phe- 

 nomenon presents much more the appearance of a field of minute 

 lumhious organs innervated by a nerve-net of an unpolarized 



