MR, G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSHL 
187 
are to a large extent novel, I have thought it desirable to insist on their theoretical 
importance rather than on that of facts which are better known, and which serve to 
uphold existing views respecting the action of ganglia. Nevertheless, even within the 
limits of the Medusae, I have found only too much reason for concluding that the full 
explanation of natural rhythm must be more complex than that which I believe to 
apply to artificial rhythm. In particular I may allude to the case of Sarsicc. The 
artificial rhythm which may be produced in the paralyzed nectocalyx of this organism 
by means of a constant stimulation is of a widely different character from that which 
occurs in the unmutilated and healthy animal. The comparatively feeble, fluttering, 
and ineffectual sequence of contraction and relaxation in the former case contrast 
strongly with the powerful, determined, and pumping-like movement in the latter 
case. Indeed, striking and suggestive as are the phenomena of artificial rhythm in 
Sarsia, none but the most prejudiced of observers could fail to perceive that it is but 
a sorry substitute for the natural rhythm of vigorous specimens. In feeble specimens, 
no doubt, the natural rhythm resembles much more closely the artificial rhythm; but 
so long as this is not the case with specimens whose ganglionic function is in a state 
of normal activity, we must conclude that this function presents some quality which a 
merely constant stimulation is not able to supply. And this function doubtless con¬ 
sists in supplying a stimulation that is periodic. So that, on the whole, my belief is 
that the natural rhythm of these tissues—and so, from analogy, of ganglio-muscular 
tissues in general—is probably due to a double process, of which one part consists in 
the periodic discharge of the ganglia, and the other in the alternate exhaustion and 
restoration of excitability of the muscles. No doubt in each species of Medusae the 
periods of ganglionic discharge are, as it were, timed to coincide with those during 
which the exhaustion of the responding tissue remains ; so that the ganglionic impulse 
is always thrown in at the moment w 7 hen the excitability of the responding tissue is at 
its climax. In this w T ay nervous energy is doubtless economised, and, if so, the natural 
rhythm becomes analogous, not to the artificial rhythm as produced by the faradaic 
current, but to the artificial rhythm as produced by single shocks of minimal intensity 
thrown in at appropriate periods. 
Thus the theory of rhythm which I now propose is not subversive of, but comple¬ 
mentary to, the current theory; I merely claim to have proved that over and above 
the already recognised factor in the production of rhythmic movement of ganglio- 
muscular tissues there is an additional factor, which, although not hitherto recognised, 
is probably of at least as much importance. 
(r.) I may fitly conclude this exposition with a brief reference to the only literature 
bearing on the subject of artificial rhythm with which I am acquainted. In the 
‘Journal of Anatomy and Physiology’ for July, 1876, there is a paper by 
Dr. M. Foster and Mr. Dew Smith which details results confirmatory of those which 
had been previously obtained by Eckhard and Heidentiain, and which are strikingly 
analogous to some of those which I have just described. The tissue on which these 
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