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MR. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OE MEDUSA. 
better than with any other kind of constant stimulation. Nevertheless, as just stated, 
other modes of constant stimulation certainly have a more or less marked effect in 
producing rhythmic response. As mentioned incidentally in my first paper, the con¬ 
stant current, during the whole time of its passage, frequently has this effect in the 
case of the paralyzed nectocalyx of Sarsia (p. 282). At the time I published that 
paper I had not observed the rhythm due to faradaic stimulation, and so suggested 
that the response in this case was “perhaps due to the hydrogen bubbles acting as 
stimulants to contraction.” Now, however, I am inclined to think, from the analogy 
supplied by the effects of the faradaic current, that the rhythmic response to the 
constant current is not due to any such accidental cause. 
With regard to other modes of stimulation, I may in the first instance refer to 
Division III., §§ 1 and 2, of my second paper. It is there stated: “ When the paralyzed 
swimming organ of Aurelia aurita is stimulated by a single mechanical irritation, it 
often responds with two, and more rarely with three contractions, which are separated 
from one another by an interval of about the same length as the normal diastole of the 
unmutilated animal.Dilute spirit, or other irritant, when dropped on the para¬ 
lyzed swimming organ of A urelia aurita, often gives rise to a whole series of rhythmical 
pulsations, the systoles and diastoles following one another at about the same rate as is 
observable in the normal swim min g motions of the unmutilated animal.” 
From this it will be seen that both in the case of mechanical and of chemical 
stimulation the same tendency to the production of rhythmic response on the part 
of the paralyzed tissues of Aurelia may be observed, as in the case of electrical 
stimulation. The principal differences consist in the rhythm being much less sustained 
in the former than in the latter case. But by experimenting on other species of 
Medusae I have been able to obtain artificial rhythm in response to mechanical and 
chemical stimulation of a much more sustained character than that which, under such 
modes of stimulation, occurs in Aurelia. I have no explanation to offer why it is that 
some species or some tissues present so much more readiness to manifest sustained 
rhythm under certain modes of stimulation, and less readiness to manifest it under 
other modes, than do other species or tissues. Probably these differences depend on 
some peculiarities in the irritability of the tissues which it is hopeless to ascertain; 
but, in any case, the fact remains that while Aurelia, Cyancea, and the covered¬ 
eyed Medusae generally, are the best species for obtaining artificial rhythm under 
the influence of faradaic stimulation, some of the naked-eyed Medusae are the best 
species for obtaining it under the influence of the constant current, and also under 
that of mechanical and chemical stimulation. I have already spoken of this effect 
of the constant current in the case of Sarsia; I shall now proceed to describe the 
effects of mechanical and chemical stimulation on the same species. 
It is but rarely that artificial rhythm can be produced in the paralyzed nectocalyx 
of Sarsia by means of mechanical stimulation, but in the case of the polypite, a very 
decided, peculiar, and persistent rhythm admits of being produced by this means. 
