170 
MR. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSAE. 
that special division of physiological inquiry to which I have referred. If, therefore, I 
have been able to detect any peculiarities in the functions of these primitive ganglionic 
tissues which have not hitherto been detected in the ganglionic tissues of higher animals, 
I cannot but consider it legitimate to attach a high degree of theoretical importance to 
such peculiarities ; for I think it then becomes legitimate to feel that such peculiarities 
ground a strong analogy in favour of the belief, that whether or not similar functions 
admit of being experimentally proved in ganglionic tissues elsewhere, such functions 
are probably present wherever ganglionic action can be shown to occur, and that 
however hopelessly these functions may be obscured by the new and complex relations 
that in other cases are involved, they nevertheless constitute in every case some among 
the fundamental properties of ganglionic tissue. 
Now, viewed in this manner, I think that the strictly rhythmic action of the 
paralyzed swimming-bell of Aurelia in answer to constant stimulation is a fact of the 
highest significance; for here we have a tissue wholly, or almost wholly, deprived of 
its centres of spontaneity, yet pulsating as rhythmically in answer to artificial stimula¬ 
tion as it previously did in answer to ganglionic stimulation.' 5 ' Does not this tend to 
show that for the production of the natural rhythm the presence of the ganglionic 
element is non-essential; that if we merely suppose the function of this element to be 
that of supplying a constant stimulus of a low intensity without in addition supposing 
the presence of any special resistance mechanism to regulate the discharges, the 
periodic sequence of systole and diastole would assuredly result; and, therefore, that 
the rhythmical character of the natural swimming motions is dependent, not on the 
peculiar relations of the ganglionic, but on the primary qualities of the contractile 
tissue ? Or, if we do not go so far as this (and, as I shall conclude by explaining, I 
am not myself inclined to go so far), must we not at least conclude that the natural 
rhythm of these tissues is not exclusively due to any mechanism whereby the discharges 
of the ganglia are interrupted at regular intervals ; but that whether these discharges 
are supposed to be interrupted or continuous, the natural rhythm is probably in a 
large measure due to the same cause as the artificial rhythm—viz.: in accordance with 
our previous hypothesis, to the alternate exhaustion and recovery of the excitable 
tissues ? This much, at least, must be allowed even by the most cautious of critics, 
viz. : that if, as current views respecting the theory of rhythm would suppose, it is 
exclusively the ganglionic element which in the unmutilated Aurelia causes the 
rhythm of the swi mm ing-motions by intermittent stimulation, surely it becomes 
a most unexpected and unaccountable fact, that after the removal of this element 
the contractile tissues should still persist in their display of rhythm under the 
influence of constant stimulation. At any rate, no one, I think, will dispute that the 
* It will not be forgotten that there are a multitude of ganglion-cells distributed throughout the 
contractile tissues of the Medusae, but forasmuch as these are comparatively rarely instrumental in 
originating stimulation, I think it is probable that artificial stimulation acts directly on the contractile 
tissues, and not through the medium of these scattered cells. 
