PULSATION WITHOUT MARGINAL SENSE-ORGANS. 



traction waves will be unimpeded circumferentially, but more or less 

 hindered radially. That this is the true explanation of the matter is 

 proven by the fact that the disk shown in figure 12, wherein the 

 circumferential cuts are numerous and the spaces between are as wide 

 as the cuts are long, will pulsate continuously. 



Mere mutilation of a disk without sense-organs will not cause it to 

 become capable of continuous pulsation. Thus the disk shown in 

 figure 20, having about 800 punctures made through its sub-umbrella 

 tissue, can not be set into a sustained rhythm. 



Although I had several hundred paralyzed disks of Cassiopea capa- 

 ble of being set into pulsation by a stimulus, such as a momentary 

 touch of a crystal of K 2 SO 4 , only one of these started into pulsation 

 of its "own accord." Ordinarily they might remain for days in the 

 aquaria awaiting the momentary stimulus which alone could call forth 

 their latent power of rhythmical pulsation. 



If disks without marginal sense-organs be set into rhythmical pul- 

 sation they move with machine-like regularity, without pauses, and 

 without any of the irregularities shown by normal Medusae with sense- 

 organs intact. Their rates of pulsation are not only practically uni- 

 form, but they are much faster than are those of the uninjured normal 

 Medusae from which the disks were prepared, as will be shown by the 

 following table : 



TABLE 2. Rate at zvhich normal Medusce of Cassiopea pulsated and the rates of 

 pulsation of their disks zvhen the sense-organs ivere excised and circumferen- 

 tial cuts "were made in the sub-umbrella . 



When disks without sense-organs are set into pulsation we may re- 

 duce the area of pulsating tissue by cutting parts of it away, but the 

 rate of pulsation will remain constant, provided we do not alter the 

 length of the circuit through which the wave must pass. If, however, 

 we make cuts in such manner as to increase the length of the circuit 



