FUNDAMENTAL EXPERIMENTS. 29 



genus Sarsia (Fig. 1) be cut completely through, so 

 that the swimming-bell instead of being closed at 

 the top is converted into an open tube, this open 

 tube continues its rhythmical contractions for an 

 indefinitely long time, notwithstanding that the 

 organism so mutilated is, of course, unable to pro- 

 gress. Thus it is a matter of no consequence how 

 small or how large a portion of contractile tissue is 

 left adhering to the severed margin of the swim- 

 ming-bell ; for whether this portion be large or 

 small, the locomotor centres contained in the 

 margin are alike sufficient to supply the stimulus 

 to contraction. Indeed, if only the tiniest piece of 

 contractile tissue be left adhering to a single mar- 

 ginal body cut out of the bell of Sarsia, this tiny 

 piece of tissue, in this isolated state, will continue 

 its contractions for hours, or even for days. 



Effects of excising the entire Margins of Umbrellas. 



Turning now to the covered-eyed division of the 

 Medusie, I find, in all th^ species I have come across, 

 that excision of the margins of umbrellas produces 

 an effect analogous to that which is produced by 

 excision of the margins of swimming-bells. There 

 is an important difference, however, between the 

 two cases, in that the paralyzing effect of the opera- 

 tion on umbiellas is neither so certain nor so com- 

 plete as it is on swimming-bells. That is to say, 

 although in the majority of experiments such 

 mutilation of umbrellas is followed by immediate 

 paralysis, this is not invariably the case; so that 



