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denser shocks, I have found that the animal gives a flash to each stimu- 

 lus (Fig. 2). The total duration of a local flash is 3 seconds, and time 

 taken to reach maximal height occupies 0.2 second. There is no 

 evidence for facilitation in my records, since each shock brings up 



Fig. 2. Flashes of the scyphomedusan Pelagia noctihica to electrical stimulation 

 (condenser shocks). Burst of 5 shocks at about 12 per minute. Time scale 

 1 per second. Stimuli added to this record represent number but not abso- 

 lute position of pulses. 



a response, and the intensity of consecutive flashes decreases in an 

 exponential fashion (Figs. 2 and 3). Indeed, this progressive decay of 

 photogeny is the most obvious feature of the records and may well be 

 obscuring facilitation in the transmission system. 



1 2 3 4 5 6 



CONSECUTIVE RESPONSES 



Fig. 3. Fatigue of consecutive responses in Pelagia noctihica. The animal was 

 stimulated with a burst of stimuli (condenser shocks) at a frequency of 1 

 per second. Upper curve, flash duration (ordinates, on right, in seconds). 

 Lower curve, decrease in intensity of Hash and in total light emitted in 

 successive flashes. © mean flash intensity. + integration of total light 

 emitted during a flash. 



