302 PHYSIOLOGICAL CONTROL IN ANIMALS 



of a single pulse, augmentation of intensity in successive responses) 

 are typical of facilitation. Observation shows that transmission is non- 

 decremental, i.e., a wave once initiated, courses over the whole surface 

 of the rachis. There are cogent reasons for believing that facilitation 



B 



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Fig. 1. Luminescent responses of the sea pansy Renilla. A, series of responses 

 to a burst of 10 electrical shocks at a frequency of 1 per second. The first 

 response appears after the third shock, and subsequent responses increase 

 progressively in intensity (facilitation). B, responses to a burst of shocks at 

 high frequency (3 per second). Note prolonged after-discharge. C, flashing 

 induced by tactile stimulation. Time scale above, 72 per minute. Recording 

 from the entire rachis. Luminous responses shown as downward deflections 

 of middle trace; electrical stimuli showai on lower line. Photomultiplier + 

 cathode-ray oscilloscope recording. 



occurs peripherally, at the neuro-effector junction, and not in the 

 synapses of the nerve net. A single tactile stimulus gives rise to a 

 wave or a series of waves, and this type of response is usually 

 ascribed to facilitation, resulting from a volley of impulses set off 

 by mechanical stimulation of receptors ( Fig. 1 ) (E.N. Harvey, 1917; 

 Pantin, 1935; Buck, 1953, 1955). 



Well-defined synapses have been recognized in medusae, and^ these 

 exhibit nonpolarized conduction (Bozler, 1927). Using contractions 

 of the umbrella as indicative of transmission phenomena, Bullock 

 (1943) finds that the nerve net of scyphomedusae is in a state of 

 permanent facilitation and transmits each impulse. Continued stimula- 

 tion, however, produces staircase, indicative of neuromuscular facilita- 

 tion. In the luminescent scyphomedusan Pelagia noctiluca tactile and 

 electrical stimulation evokes a glow which may spread in some 

 animals as a wave over the surface of the bell (Panceri, 1872b; 

 Heymans and Moore, 1924; Moore, 1926). By stimulating with con- 



