504 G. H. PARKER 



zooids; thus a direction the reverse of that implied by Miiller 

 was suggested. Possibly the current may take either direction, 

 depending upon circumstances. These are questions, however, 

 that must be tested out on living material. The point to be 

 emphasized here is that, though the autozooids are extremely 

 independent in their individual activities, they may be unified 

 in a measure in their actions by the single organ for inflation, 

 the rhythmically contracting peduncle, which thus serves the 

 colony as a whole. 



Although the autozooids of Renilla exhibit great independence 

 in activity and give evidence of only a slight unifying principle 

 that is almost purely mechanical, there is another feature in the 

 activities of this pennatulid that exhibits for the colony a much 

 more fundamental form of unity. This is its phosphorescence. 

 This peculiarity of Renilla was long ago observed by Agassiz 

 ('50, p. 209), and in consequence of the brightness of the light 

 produced by this form it has commonly been listed among the 

 highly phosphorescent animals (Mangold, '10-14, p. 250). 

 Its phosphorescence is characteristic of the night. If a living 

 specimen during the day is carried into a dark room and stim- 

 ulated, it will show no phosphorescence. If it is stimulated at 

 night by being prodded with a blunt implement or by the ap- 

 plication of a faradic current, waves of light will be seen to run 

 over the superior surface of its rachis. That the phosphorescence 

 is developed in the dark can be seen by keeping Renilla away 

 from the light during daytime. Such an animal, after having 

 been put in "the dark, will show no trace of phosphorescence for 

 some time. After an hour or two, depending upon the inde- 

 vidual, a few phosphorescent points will appear on stimulation, 

 and in from two to three hours waves of phosphorescence will 

 course over the whole colony at each stimulus much as they do 

 at night. This condition may be maintained so long as the an- 

 imal is kept in the dark. It is lost in a quarter to half an hour 

 after the animal is returned to the light. In this respect Re- 

 nilla is like the ctenophore Mnemiopsis, whose phosphorescence, 

 as shown by Peters ('05), develops in the dark, but is inhibited 

 in the light. 



