INHIBITION OF ANIMAL LUMINESCENCE BY I.KiHT. 87 



dactylus (large arc, 4 min.); Heteroteuthis dispar (small arc, 

 3 min.). 



As to inhibition of fireflies, I have observed no inhibition of 

 the luminous organ of Photuris pennsylvanica removed from the 

 body and mashed on a slide (so that it luminesced continuously) 

 after 4 minutes' exposure to 15,000 foot-candles. However, 

 when the luminous organ (alone) in the intact animal is directly 

 exposed to the above light, the normal flashes of the animal as 

 well as the flashes from electrical stimulation (of the thorax) 

 are inhibited and remain so for some seconds after the light is 

 screened. Illumination of the eyes by 15,000 foot-candles while 

 keeping the luminous organ in the dark does not inhibit the 

 flashing. 



Pyrophorus noctilucus sent to Woods Hole from Cuba shows no 

 inhibition of the teased organ in 15,000 foot-candles illumination 

 but if one of the two thoracic organs is exposed to sunlight or 

 the carbon arc light (passing through water) for two minutes, 

 while it is glowing steadily, it will be observed that this exposed 

 organ now glows less strongly than the other in the dark. 



We are evidently dealing in these cases with no true inhibition 

 of luminescence of luminous material but with an effect of light 

 on the local nerve mechanism of stimulation in the organ itself, 

 a process quite different from that in Cypridina. 



It will thus be observed that inhibition of luminescence is 

 rather rare and that Ctenophores and Cypridina remain the 

 best known cases. Noctiluca and the Dinoflagellates need re- 

 investigation and it is possible that some species of copepods 

 show inhibition. A large number of other forms do not. 



In Cypridina the inhibition is due to acceleration of the 

 spontaneous (without luminescence) oxidation of luciferin. 

 Light has no inhibiting effect in absence of oxygen. This 

 probably explains why the whole Cypridinas are not inhibited, 

 for the great mass of luciferin must be kept under anaerobic 

 conditions in the gland. 



I have also investigated the Ctenophores to determine if their 

 luminescence was inhibited by light in absence of oxygen and 

 was surprised to find inhibition by light when the last traces of 

 oxygen were removed from a Beroe, Eucharis or Mnemiopsis 



