SECTION OF COVERED-EYED MEDUSA, 73 
would happen that such nerves would escape the 
section for a longer distance. It is indeed incredible 
that any one nerve should happen to pursue a spiral 
course twice or thrice round the umbrella, and at 
the same time happen to be concentric with the 
course pursued by the section; but, as we shall 
presently see, such an hypothesis 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 completely 
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 contraction-wave, 
and so very 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 highly interesting paper recently published by Dr. W. H. 
Gaskell, F.K.S., on “The Innervation of the Heart’? (Journ. of 
Physiol., 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 
