nS 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 



FlG. 3. Showing non-importance of any definitely localized center in maintaining 



rhythmical pulsation. 



every part of the ring in succession as it passes. \\e 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, 



