FUNDAMENTAL EXPERIMENTS. 27 



walls of the bell are drawn together ; the capacity 

 of the bell being thus diminished, water is ejected 

 from the open mouth of the bell backwards, and the 

 consequent reaction propels the animal forwards. 

 In these swimming movements, systole and diastole 

 follow one another with as perfect a rhythm as 

 they do in the beating of a heart. 



Effects of excising the entire Margins of Nectocalyces. 



Confining our attention under this heading to 

 the naked-eyed Medusae, 1 find that the following 

 proposition applies to every species of the group 

 which I have as yet had the opportunity of ex- 

 amining : Excision of the extreme margin of a 

 nectocalyx causes immediate, total, and jyermanent 

 'paralysis of the entire organ. Nothing can possibly 

 be more definite than in this highly remarkable 

 efi'ect. I have made hundreds of observations upon 

 various species of the naked-eyed Medusae, of all 

 ages and conditions of freshness, vigour, etc. ; and I 

 have constantly found that if the experiment be 

 made with ordinary care, so as to avoid certain 

 sources of error presently to be named, the result is 

 as striking and decided as it is possible to desire.* 

 Indeed, I do not know of any case in the animal 

 kingdom where the removal of a centre of spon- 

 taneity causes so sudden and so complete a paralysis 



* I have only met with one individual exception. This occurred 

 in a specimen of Staurophora laciniata, where, after removal of 

 the entire margin, three centres of spontaneity were found to 

 i-emain in the sheet of contractile tissue lining the nectocalyx. 



