MR. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSAE. 
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facts which I have adduced justify us in reconsidering the whole theory of rhythm as 
due to ganglia. 
(k.) As I have already said, I am not inclined to deny that there is probably some 
truth in the current theory of rhythm as due to ganglia ; I merely wish to point out 
distinctly that this theory is inadequate, and that in order to cover all the facts, it 
will require to be supplemented by the theory which I now propose. The current 
theory of rhythm as due to ganglia attributes the whole of the effect to the gan¬ 
glionic element, and thus fails to meet the facts of a rhythm which is artificially 
produced after the ganglionic element has been removed. It also fails to meet a 
number of other facts of the first importance. For it is beyond all doubt that 
rhythmic action of the strictest kind occurs in an innumerable multitude of cases 
where it is quite impossible to suppose anything resembling ganglia to be present. 
Not to mention such cases as the Snail’s heart, where the most careful scrutiny has 
failed to detect the least vestige of ganglia, but to descend at once to the lowest 
forms of animal and vegetable life, rhythmic action may here be said to be the rule 
rather than the exception. The beautifully regular motions observable in some Algee, 
Diatomacese, and Ocillatorise, in countless numbers of Infusoria, antherozoids, and 
spermatozoa, in ciliary action, and even in the petioles of Hedysarum gyrans, are all 
instances (to which many others might be added) of rhythmical action where the pre¬ 
sence of ganglia is out of the question. Again, in a general way, is it not just as we 
recede from these primitive forms of contractile tissue that we find rhythmic action to 
become less usual ? And, if this is so, may it not be that those contractile tissues 
which in the higher animals manifest rhythmic action are the contractile tissues which 
have longest retained their primitive endowment of rhythmicality ? To my mind it 
seems hard to decide in what respect the beating of a Snail’s heart differs from that of 
the pulsatile vesicles of the Infusoria; and I do not think it would be much easier to 
decide in what essential respect it differs from the beating of the Mammalian heart. 
The mere fact that the presence of ganglia can be proved in the one case and not in 
the other, seems to me scarcely to justify the conclusion that the rhythm is in the one 
case wholly dependent, and in the other as wholly independent, of the ganglia. At 
any rate, this fact, if it is a fact, is not of so self-evident a character as to recommend 
to us the current theory of ganglionic action on d priori grounds. 
(1.) Coming, then, to experimental tests, we have already seen that in the de- 
ganglionated swimming organ of Aurelia aurita, rhythmic response is yielded to 
constant faradaic stimulation of low intensity. The next question, therefore, which 
presents itself in relation to our subject, is as to whether other modes of constant 
stimulation elicit a similar response. Now, in a general w r ay, I may say that such is 
the case, although I have chosen faradaic stimulation for special mention, because, in 
the first place, its effect in producing rhythmic action is the most certain and precise, 
and, in the next place, the effects of administering instantaneous shocks at given 
intervals admit of being compared with the effects of constant faradaic stimulation 
