NATURAL KHYTHM. 163 



tracfcing, how are we to know whether the action 

 of the ganglia is truly automatic, or sustained 

 from time to time by stimuli proceeding from other 

 parts of the organism ? In most cases experiments 

 cannot be conducted with reference to this question, 

 but in the case of the Medusae the^^ may be so, and 

 it was with the view of throwing: lic^ht on this 

 question that the experiments just described were 

 made. Now in these experiments the fact is 

 sufficiently obvious that mutilations of any part of 

 the organism modify the rhythm of the marginal 

 ganglia most profoundly. That this modification 

 does not proceed from shock, would seem to be 

 indicated by the facts that the first efiect of the 

 mutilation is to quicken the rhythm; that there is a 

 sort of general proportion to be observed between the 

 amount of tissue abstracted and the deo-ree of sloAvinor 

 of the rhythm produced; and that the slowing efiects 

 continue for so long a time. All these facts seem 

 to show that we have here something other than 

 mere shock to deal with. 



A strong suspicion, therefore, arises that the cause 

 of the slowing of the rhythm which results from 

 removing the manubrium, or a part of the general 

 contractile tissue of the bell, consists in the destruc- 

 tion of some influence of an afi[erent character which 

 had previously emanated from the parts of the 

 organism which have been removed, and that 

 the normal rhythm before the operation was partly 

 due to a continuous reception, on the part of the 

 ganglia, of this aflferent or stimulating influence. 

 In support of this view are the facts that the first 



