LUMINESCENCE 



571 



at frequencies ranging from 5-12/sec, the whole series ending within a 

 few seconds (Fig. 13.26(d)). When small pieces of a meridional canal are 

 stimulated with brief shocks, a single flash follows each electrical pulse 

 (Fig. 13.26(e)). Data for flash duration are summarized in Table 13.3. 

 Some characteristics of the local responses are as follows: the light 

 intensity varies directly with the voltage and duration of stimulation (above 

 threshold); latent period is reduced by increase in strength of stimulation; 

 several sub-threshold stimuli summate to produce a flash ; rapid repetitive 



"7 7 7 7 7 T 



CM 



Y mnnr 



(C) 



OS sec 



en 



jjjjULUJJJlJu 



UiMlMUl^^ 



Fig. 13.26. Photo-electric Recordings of the Luminescent Responses 

 of Coelenterates and Ctenophores 



(a) Flashing of the sea pansy Renilla, induced by electric shocks; (b) flashing of the 

 sea pen Leioptilus, evoked by a series of electric shocks; (c) Leioptilus: persistent rhyth- 

 mic flashing following a period of stimulation. Time scale in records a-c, 72/min, 

 shown above; stimuli on lower line. Flashes appear as downward deflexions of the 

 middle trace, (d) Multiple responses from a meridional canal of Mnemiopsis, each series 

 induced by a single shock; (e) Mnemiopsis: responses from a small section of a meridional 

 canal, showing increase in intensity of flash when the voltage is raised; (/) Mnemiopsis: 

 facilitation of luminescent responses under repetitive stimulation(l/sec). (Records d-f 

 from Chang (14).) 



stimulation, above 10 sec, produces summation of responses. It is also 

 observed, at slow rates of stimulation (<5/sec), that consecutive discrete 

 responses increase progressively in intensity, indicating the operation of 

 some facilitatory phenomenon (Fig. 13.26(f)). It has not yet been estab- 

 lished whether these local responses, recorded from small pieces of a 



