718 
ME. G. J. EOMANES ON THE LOCOMOTOE SYSTEM OE MEDTJS2E. 
of the irritable surface of Aurelia is stimulated too gently to start a contractile wave , it 
may nevertheless he sometimes observed that those tentacles which are nearest to the 
seat of stimulation respond with a sudden contraction, then those next adjacent to them 
on either side do the same, and so on — there being thus started in the margin two im- 
pulses which travel with equal rapidity in opposite directions, and the passage of w r hich 
is marked by the successive and intensely sudden retraction of the numberless tentacles 
by which the margin is fringed. This most beautiful expression of the passage of a wave 
of stimulation does not occur in all, or even in most, specimens of Aurelia . It may best 
be seen in specimens that are perfectly fresh and vigorous — i. e., in general, such as are 
deeply coloured. Moreover, iust as in the case of reflex action, so in this case, the wave 
of stimulation may be started from some tracts more certainly than from others, 
although there is no constancy as to the position of these tracts in different indivi- 
duals. As showing the identity of the wave of stimulation in this case and in that 
of reflex action, I may mention the following fact. When a single lithocyst is left in 
situ and a point in the nervo-muscular sheet at a distance from the lithocyst is gently 
irritated, if the passage of the stimulus happens to be marked by the above-described 
occurrence of what we may term a tentacular wave, it is always observable that the 
lithocyst never originates its reflex response until after the tentacular wave has reached 
it, and that it then invariably does so when the requisite period of latent stimulation 
has elapsed, viz. about half a second after the arrival of the tentacular wave. This 
experiment may be rendered particularly fascinating if the Aurelia has been pre- 
viously cut into a broad strip, in such a way as to leave the single remaining litho- 
cyst at one end ; for on now irritating the other end of this strip, the tentacular wave 
may be observed to run continuously in the same direction all the way along the 
margin, and then, after it reaches the terminal ganglion and the period of ganglionic 
latency has elapsed, the contractile wave which it has been the means of starting from 
the ganglionic end of the strip courses all the way along the latter in the opposite 
direction to that which the tentacular wave had previously pursued. 
In connexion with these tentacular waves I may further state that it does not signify 
how much of the tentacular rim is removed from the organism ; for, however small a 
number of tentacles are left adhering to the margin, they exhibit the same action as when 
the whole series is intact. 
( d ) Now the occurrence of these tentacular waves is invaluable for the purpose of 
the experiments next to be described. These experiments consist in submitting the 
swimming-bell of Aurelia to various forms of section, with the view of ascertaining 
the extent to which the nervo-muscular tissues may be thus mutilated without suffering 
loss of their excitational continuity. The importance of any facts established by these 
experiments will doubtless be appreciated, in view of the theoretical standing of the 
analogous facts which we have so recently been considering with regard to con- 
tractional continuity. Of course the value of tentacular waves in these experiments 
consists in the circumstance that they never occur except in response to stimulation. 
