310 



PHYSIOLOGICAL CONTROL IN ANIMALS 



observations for the enteropneust Ptychodera bahamensis, in which 

 luminescence is elicited with diflSculty by tactile stimulation after 

 exposure to light. The photocytes themselves appear to be unaffected 

 by illumination since they still respond normally to electrical stimula- 

 tion (Crozier, 1917). 



Another form of inhibition is theoretically possible for intracellular 

 luminescence. One can picture an animal in which photogeny is 

 normally the active phase at the effector level and is continuous in the 

 absence of external control. Inhibitory fibers would then act by 

 suppressing light emission. Analogies are at hand in the transitory 

 inhibition of continuous ciliary activity, as in veliger larvae (Carter, 

 1926). In fireflies, Buck (1948) has described four types of light 

 emission, ranging from continuous glow to quick flash, and suggests 

 that these may represent progressively more effective modes of con- 

 trol. Fireflies showing the continuous glow are unable to control the 

 response; intermittent glow and flash represent various levels of con- 

 trol. It is still uncertain how control is achieved, but it can be argued 

 that it involves some form of inhibition, either by direct nervous 

 influence, or by restriction of oxygen supply. Records of induced 

 luminescence in Lampyris noctiluca are shown in Fig. 7. 



B 



iMMimir 



Fig. 7. Luminescent responses of the European firefly Lampyris noctiluca to 

 electrical stimulation. Electrodes were positioned over the ventral body vrall 

 and stimuli consisted of condenser shocks. A, short burst at a low frequency 

 (2-second burst of 11 pulses at 7 per second). B, 2-second burst at 18 per 

 second (28 pulses). C, short burst (16 pulses), and D, a long burst (28 

 pulses), at 8 per second. E, long burst of 90 pulses at 8 per second. Heavy 

 horizontal hne on bottom trace indicates position and duration of stimula- 

 tion. Time scale above, 1 per second. 



