CONTRIBUTIONS FROM THE ZOOLOGICAL L.\BOILA.TORY OF THE MUSEUM 

 OF COMPARATIV'E ZOOLOGY AT HARVARD COLLEGE. E. L. MARK, 

 Director. — No. i6':. 



PHOSPHORESCENCE IN CTENOPHORES. 



AMOS W. PETERS. 



INTRODUCTION. 



The problems discussed in this paper are the localization of the 

 power of phosphorescence in mature and in young ctenophores, 

 and the influence of certain factors, such as mechanical stimula- 

 tion, light, and heat, upon the ability of these animals to phos- 

 phoresce. 



The species upon which I have worked is the common summer 

 ctenophore, Mnemiopsis leidyi A. Agassiz. These animals were 

 to be found at Wood's Hole, Mass., abundantly during August, 

 1902 and 1903. The phenomenon of phosphorescence which 

 they exhibited in their native sea-water when mechanically 

 agitated after dark was suggestive of laboratory experiments. 



In my experiments I found it necessary to use a dark chamber, 

 which I constructed from a simple pine box heavily covered jfirst 

 with paper and then with several layers of black cloth. The dark 

 box was placed upon a table before the experimenter and its open 

 front was provided with overhanging cloth, sufficient to include 

 his head and shoulders. This arrangement permitted both the 

 observation of phosphorescence and the free use of the experi- 

 menter's hands for agitating the ctenophores, etc. This appara- 

 tus was not quite as efficient as a dark room, yet it was adequate 

 for the work that was attempted in it. As observation of the 

 animals required the continuous attention of the experimenter in 

 the dark-box and as light must be excluded, the time was read and 

 recorded by an assistant upon signals from the experimenter. 

 This procedure also favored the adjustment of the experimenter's 

 eye to the conditions of observation after the change from daylight 

 to darkness. The time here recorded was read to tenths of a 

 minute, and differences so small as this are nowhere of conse- 



