186 
MR. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSiE. 
(q.) I will now sum up this rather lengthy discussion. The two theories of gan¬ 
glionic action may be stated antithetically thus : In both theories the accumulation of 
energy by ganglia is supposed to be a continuous process ; but while the resistance 
theory supposes the rhythm to be exclusively due to an intermittent and periodic 
discharge of this accumulated energy on the part of the ganglionic tissues, the 
exhaustion theory supposes that the rhythm is largely due to a periodic process of 
exhaustion and recovery on the part of the responding tissues. Now, I submit that 
my experiments have proved the former of these two theories inadequate to explain 
all the phenomena of rhythm as it occurs in the Medusae. For these experiments have 
shown that even after the removal of the only ganglia which serve as centres of natural 
stimulation, the excitable tissues still continue to manifest a very perfect rhythm under 
the influence of any mode of artificial stimulation (except heat), which is of a constant 
character and of an intensity sufficiently low not to produce tetanus. And as I have 
proved that the rhythm thus artificially produced is almost certainly due to the 
alternate process of exhaustion and recovery which I have explained, there can scarcely 
be any doubt that in the natural rhythm this process plays an important part, parti¬ 
cularly as we find that temperature and gases exert the same influences on the one 
rhythm as they do on the other. And, as an additional reason for recognising the 
part which the contractile tissues probably play in the production of rhythm, I have 
pointed to the fact that in the great majority of cases in which rhythmic action occurs, 
the presence of ganglia cannot be suspected. For it is among the lower forms of life, 
where ganglia are certainly absent, and where the functions of stimulation and con¬ 
traction appear to be blended and diffused, that rhythmic action is of the most frequent 
occurrence ; and it is obvious with how much greater difficulty the resistance theory is 
here beset than is the one which I now propose. Granted a diffused power of stimu¬ 
lation with a diffused power of response, and I see no essential difference between the 
rhythmic motions of the simplest organism and those of a deganglionated Medusa in 
acidulated water. 
But now, in conclusion, I wish it to be distinctly understood that I am not attempt¬ 
ing to overturn, but merely to supplement, the current theory of ganglionic action. 
My belief is that this theory is to a large extent a true one, but that in order to 
become a complete theory it must incorporate the facts and inferences which have now 
been fully detailed. By a complete theory I mean, of course, a theory which will 
cover all the facts; and forasmuch as the facts on which my inferences are founded 
of this organ at a small cost of nervous energy. How far the rhythm of the nectocalyx is to be attributed 
to the resistance mechanism of the ganglia, and how far to the alternate exhaustion and recovery of the 
contractile tissues, I think it is impossible to determine, seeing that it is impossible exactly to imitate the 
natural ganglionic stimulation by artificial means. But it is, I think, of importance to have ascertained 
at least this much : that in Sarsia the tonus of one organ and the rhythm of another, which apparently 
both received their stimulation from the same ganglia, must at any rate in part be attributed to a differ¬ 
ential irritability of these organs as distinguished from their differential stimulation. 
