SECTION OF COVERED-EYED MEDUSiE. 73 



would happen that such nerves would escape the 

 section for a longer distance. It is indeed incredible 

 that anyone nerve should happen to pursue a spiral 

 course twice or thrice round the umbrella, and at 

 the same time happen to be concentric witli the 

 course pursued by the section ; but, as we shall 

 presently see, such an hy})othcsis as this is not 

 necessary to account for the facts. 



Again, in the second place, strong evidence that 

 the passage of the contraction-waves is dependent 

 on the functional activity of the nervous plexus, 

 and therefore that they are not merely muscle- 

 waves, is furnished by the fact that at whatever 

 point in a spiral strip which is being progressively 

 elongated by section the contraction-wave becomes 

 blocked, the blocking is sure to take place coinjMely 

 and exclusively at that point. Now, as I have tried 

 this experiment a great number of times, and 

 always tried it by carefully feeling the way round 

 {i.e. only making a very short continuation of the 

 cut after the occurrence of each con tract ion- wave, 

 and so ver}^ precisely localizing the spot at which 

 the contraction- wave ceased to pass), I can scarcely 

 doubt that in every case the blocking is caused by 

 the cutting through of nerves.* 



* In a liighly interesting paper recently published by Dr. W. H. 

 Gaskell, F.K.S., on " The Innervation of the Heart" (Journ. tf 

 Physiol. y vol. iv. p. 43, et seq.), it is shown that the experiments 

 in section thus far described yield strikingly similar results when 

 performed upon the heart of the tortoise and the heart of the 

 skate. Dr. Gaskell inclines to the belief that in these cases 

 the contraction-waves are merely muscle-waves. There is one 

 important fact, however, which even here seems to me to indicate 



