166 THE ELEMENTARY NERVOUS SYSTEM 



that is necessary to keep up continuous pulsing. How, 

 under normal conditions, the eight or more centers in a 

 pulsing bell are coordinated has been a question of much 

 interest. Romanes (1878) has shown, that if a scypho- 

 medusa is partially subdivided by radial cuts that run 

 from the edge of the bell well toward its center and alter- 

 nate with the marginal bodies so that each segment thus 



Fip. 42. -Diagram of a jellyfish Aurelia whose bell has been deeply incised in a radial 

 direction at eight places reducing it thus to partial octants each one of which carries a mar- 

 ginal body. As shown by the experiment of Romanes, each octant has its own rate of pulsing. 



formed carries a single one of these bodies (Fig. 42), 

 the segments thus formed continue to pulse but not in 

 unison, for each will have its own rate. Loeb (1899) has 

 shown that the apparent coordination of the group of 

 marginal bodies or like organs in the medusae is due not 

 to a coordinating center but to a condition such as is seen 

 in the radially cut bell, except that in the normal bell the 

 response from the marginal body that for the moment 

 has the most rapid rate stimulates all the others to action 

 and thus one body temporarily controls the whole bell. 



