118 Papers from the Marine Biological Laboratory at Tortugas. 
The point which was stimulated and from which the contraction-wave 
first arises is of no more importance in maintaining the rhythmical move- 
ment than is any other point on the ring. My conclusions of 1906 are 
erroneous in this respect, for the wave is not reinforced and sent forth anew 
every time it returns to its place of origin, but is maintained by each and 
OOG 
OGG 
L 
Fic. 3.—Showing non-importance of any definitely localized center in maintaining 
rhythmical pulsation. 
= 
every part of the ring in succession as it passes. We may prove this by 
causing the wave to originate at some definite point and then cutting away 
the tissue around this point; yet the wave continues unhindered through 
the circuit. Fig. 3, A-L will serve to illustrate this non-importance of any 
definitely localized center in maintaining the circuit-waves. For example, 
