JELLYFISHES 109 



demonstrating how small an amount of tissue is neces- 

 sary for the transmission of a wave. 



In Cassiopea, Mayer (1906, 1908) has shown that the 

 two waves that emerge from the single marginal body 

 are often of very different sizes. When two such dispro- 

 portionate disturbances meet on the opposite side of the 

 bell, the stronger wave commonly overcomes the weaker 

 one and instead of having both disappear the stronger one 

 continues its course around the bell. Such a wave once 

 started may course indefinitely round and round a bell. 

 This is particularly true if the bell has been so cut as to 

 produce a very long circular stretch so that after the 

 passage of the wave over a given portion of the stretch 

 that portion has ample time to recover before the wave 

 again passes over it. Harvey -(1912) found that such a 

 "trapped" wave may course over a circular path for as 

 long as eleven days with no appreciable decline in rate. 

 As this rate in Cassiopea averaged 46,472 millimeters per 

 minute, the wave must have travelled in the eleven days 

 somewhat over 457 miles. 



As Eimer, Bomanes, Mayer, and others have shown, 

 jellyfish bells may be cut into patterns of the utmost di- 

 versity without, however, preventing the passage of their 

 waves of contraction. As the majority of these patterns 

 interrupt completely the course of the muscle fibers, but 

 would always be circumvented by the nerve-net, it is gen- 

 erally assumed that transmission over the complicated 

 outline to which the body of the jellyfish has been reduced 

 must be dependent upon the nerve-net, not the muscles. 



More conclusive evidence of the significance of the 

 nerve-net in this respect, as contrasted with the muscle 

 layer, has been obtained from several lines of work. Bethe 

 (1903, 1909) has pointed out that in Rhizostoma the 



