32 Papers from the Marine Biological Laboratory at Tortugas. 



When a simple contraction-wave breaks up into two or more wavelets, 

 the one following the other, the rate declines, for strong stimuli travel faster 

 than weak ones; and if an originally unitary wave divides into two, the 

 stimulus represented by each component wavelet is naturally less than that 

 of the wave as a whole. Thus a ring which gave i68 pulsations per minute 



^l\^lwv^/\/^/\N\^^/^AN^^^^ 



Fig. 2. 

 with a unitary wave gave only 132 per minute when this wave broke into 

 two component wavelets, the one following the other around the ring. 

 Moreover, if two waves follow one behind the other, the tissue does not 

 enjoy so long a resting-period as if one simple wave were in the circuit, 

 and a certain time must be permitted to pass before the muscles which have 

 responded by a contraction can again fully respond to another stimulus. 

 In some rings the tissue may give a strong response only to every alternate 

 or even every third return of the wave, showing that the muscles which 

 have very recently contracted can not again give a maximal response until 

 a certain resting-time has elapsed. This was first observed in the muscles 

 of Scyphomedusae by Romanes, 1885, and has been studied in detail by 

 Bethe (1903 and 1908). (See line 6 of fig. i.) 



For these reasons, a double wave caused by the breaking up of an 

 originally unitary impulse moves slower than did the parent wave. Gener- 

 ally speaking, when a ring is first set into pulsation by electrical stimulation, 

 there are a number of secondary wavelets, but these soon fuse into a single 

 simple wave, and this unitary wave then rarely breaks into component parts. 



In Cassiopea, as in Linmlus, the stimulus which produces pulsation is 

 neurogenic, the muscles being incapable of spontaneous pulsation if the 

 nervous system be eliminated. Thus a o.oi molecular solution of oxalic 

 acid in sea-water is extremely toxic to the motor centers and nerves of 

 Cassiopea, a very short immersion preventing the rhopalia from ever again 

 giving rise to the pulsation-stimulus. The muscles, however, still remain 

 capable of contracting when stimulated directly. 



In this connection, Harvey found that in most of the amines and in 

 inorganic hydroxides the nerves cease to conduct before the muscles lose 



