ME. Gr. J. EOMANES OX THE LOCOMOTOE SYSTEM OE MEDTJS2E. 
697 
admits of one part responding to stimuli applied at another part, whether or not con- 
tractile loaves are able to pass along the intervening parts * . 
With this distinction clearly understood, I shall now proceed to describe some expe- 
riments which were devised in order to test the amount of section that the excitable 
tissues of Sarsia would endure without suffering loss of their excitational continuity. 
The experiments detailed in the foregoing subsections were really experiments of this 
kind ; but such experiments derive a special interest when conducted on the general 
contractile-sheet of the Medusae. They do so because, as we have already seen, there is 
here decided indication of a nervous plexus ; and it will be remembered that some of the 
most interesting questions with which my last paper was concerned, and which it left 
unanswered, were, first as to the presence of such a nerve-plexus, and next as to the 
extent in which, if present, it was differentiated from the muscular element. 
Now, as stated in my former paper, the contractile tissues of Sarsia will endure very 
severe forms of radial and spiral section without suffering loss of their contractional 
continuity ; but I find that, as a rule, their tolerance is not nearly so great as regards the 
maintenance of their excitational continuity. To save space I will only give one average 
Eig. 6. 
case. The figure (fig. 7) represents a specimen of Sarsia spread flat on an object-glass 
after having been slit open along one side. The experiment consisted in determining the 
* I choose these terms, because they are the only ones I can think of to express the meaning I wish to convey. 
There is evidently a broad distinction — and a very important one for the purposes of this paper — between the 
passage of a contractile wave from the point of stimulation A to the point of destination B, and the passage of 
an unseen molecular wave from A to B, the existence of which is only rendered apparent by the response at B 
to the stimulus applied at A. And as it is further evident that this distinction has reference to the most fun- 
damental quality wherein the function of nerve is distinguished from that of muscle, viz. the power of setting 
up responsive contractions at a distance from the seat of irritation, it will he understood that by the term 
“ excitational continuity ” I intend to denote the first indications we can perceive in the animal kingdom of 
the distinguishing function of nerve-tissue. The terms which I have employed are not to he found in our 
standard dictionaries ; but their introduction is justified by the analogy of such words as “ emotional,” “ sen- 
sational,” &c. 
