MR. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSiE. 169 
strong' contraction, and therefore the result on the tracing is a slight depression in 
the otherwise even curve of ascent. Lest any doubt should arise from the smallness 
of the curves representing the weak contractions that the former are in some way 
accidental, I may draw attention to the fact that the period of latent stimulation is the 
same in the case of all the curves. To render this apparent I have placed marks 
below the smaller curves, which show in each case the exact point where the depressing 
effect of these smaller curves on the ascending sweeps of the larger curves first become 
apparent, i.e., the point at which the feeble contraction begins. Now, what I wish to 
be gathered from the whole tracing is this : If the strength of the induction shocks 
had been much greater than it was, all the contractions would have become strong 
contractions, and tetanus would have been the result. But, as the strength of the 
induction shocks was only slightly more than minimal, the exhaustion consequent on 
every strong contraction so far diminished the irritability of the tissue that when, 
during the process of relaxation, another shock of the same intensity was thrown in, the 
stimulus was only strong enough, in relation to the diminished irritability of the partly 
recovered tissue, to cause a feeble contraction. And these facts tend still further 
to substantiate the hypothesis whereby I have sought to explain the phenomena 
of artificial rhythm. 
(j.) Upon the whole, then, I think that this hypothesis may be properly accepted 
as a full explanation of the artificial rhythm; but whether or not the hypothesis is thus 
accepted, the facts which it is adduced to account for remain as remarkable and signi¬ 
ficant as they were before. That these facts are remarkable no one will dispute ; the 
degree of their significance will depend on the degree in which the inferences I draw 
from them appeal - to other physiologists of the same legitimate character as they appear 
to myself. These inferences will perhaps be considered somewhat bold, as they 
certainly must be considered premature ; and were it not that I think physiology may 
gain, while it cannot lose, from healthy speculation on such facts as those which are 
now before us, I should prefer to postpone for the present any further treatment of 
this subject. Nevertheless, as all the experiments I have hitherto made tend, without 
exception, to substantiate my views, it will at least be interesting to describe those 
experiments in connexion with the theory which led to their being tried. The theory 
in question is a theory of ganglionic action in general. 
I think every one will feel it to be obviously true that if ganglionic action is ever to 
receive any considerable elucidation, the Medusae are by far the most promising 
structures to yield it. In them we have the first observed appearance, in the ascend¬ 
ing scale of animal life, both of nervous and of muscular elements. These elements are, 
therefore, presumably here present in their simplest or most primitive forms. Again, 
the organisms are of all sizes, from less than that of a pea to more than that of a 
parasol; their endurance under experimentation is as great as can be desired; in their 
different species they present countless modifications of structure, and, in general, they 
present what one may regard as a typically perfect class of tissues for the purposes of 
MDCCCLXXX. Z 
