ME. Gr. J. ROMANES ON THE LOCOMOTOE SYSTEM OE MEDUSAS. 
749 
although themselves incapable of originating a spasm in response to stimulation, are 
nevertheless so wonderfully capable of conducting a spasm when this has been originated 
by irritation of the slender tissue-tracts above named. It is as though every fibre of 
the general contractile tissue were capable of liberating energy in either of two very dif- 
ferent ways, and that whenever one part of the general mass is made to liberate its 
energy in one of these two ways, all the other parts of the mass do the same — and this 
no matter how far through the mass the liberating process may have to extend. And 
to say that it is the ganglionic element in the margin which, to recur to our previous 
metaphor, here acts as a detonator, is not to explain the facts ; for although it would 
be an interesting thing to know that a ganglion-cell may be able to originate two different 
kinds of impulse according as it liberates its energy spontaneously or in answer to direct 
stimulation, this knowledge would merely serve to transfer the questions which now 
apply to the marginal and radial tube-tissues in general to the ganglionic tissues in par- 
ticular. Again, the supposition of the ganglia acting as detonators when themselves 
directly irritated, would not explain why it is that the contractile tissues are capable of 
two such very different kinds of response. Anaesthetics block spasmodic waves, but not 
till they have suspended spontaneity, and even destroyed muscular irritability as regards 
direct stimulation. 
In Av/relia aurita the passage of a tentacular wave marks the passage of a stimulus- 
wave. Such waves may be started more readily by stimulating some tracts than by sti- 
mulating others, though there is no constancy as to position of these tracts in different 
individuals. The case of stimulus-waves in this particular, therefore, resembles that of 
contractile waves, which, as explorations by graduated stimuli show, may also be more 
readily started from some tracts than from others. Again, the two cases resemble one 
another in the. still more important particular of the astounding degree to which the 
tissues may be mutilated without their physiological connexions being destroyed. For 
excitational continuity being thus shown as difficult to destroy, in the case of this 
Medusa, as is contractional continuity, we are led to conclude, for reasons which I need 
not repeat, that both these functions are probably dependent on the same tissue-elements. 
And, in any case, the fact that the essentially nervous function of maintaining excita- 
tional continuity is able to persist in these primitive nervous tissues after they have been 
submitted to the severest possible forms of section, is a fact the significance of which, it 
seems to me, can scarcely be overrated. The fact itself cannot be explained by Klein- 
enberg’s theory of double-function cells ; for sometimes contractile waves will become 
blocked by section before the tentacular waves, and sometimes vice versd. We seem, 
therefore, driven upon the theory of a nerve-plexus whose constituent elements are 
capable of vicarious action in almost any degree. This theory is supported by the results 
of explorations with graduated stimuli, and also by the consideration that in Sarsia, 
which is a more highly integrated form than Aurelia , the supposed plexus is so far dif- 
ferentiated that vicarious action on the part of its constituent elements is usually possible 
in but a low degree. Again, Tiaropsis appears to stand midway between Sarsia and 
