MR. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSAE. 175 
motionless nectocalyx a single stimulation. The interpretation of these facts would 
seem to be that the general irritability of the excitable tissues is exalted by the universal 
and constant stimulus supplied by the acid to an extent that is just bordering on that 
which gives rise to rhythmic movement, so that when the violent contraction is given 
in response to the mechanical stimulus, the disturbance serves to start the rhythmic 
movement. 
If a paralyzed nectocalyx, while manifesting its artificial rhythm in acidulated sea¬ 
water, be suddenly transferred to normal sea-water, the movements do not cease 
immediately, but continue for a considerable time. This fact can easily be explained 
by the very probable, and indeed almost necessary, supposition that it takes some time 
after the transference to the normal sea-water for the acid to be washed out from 
contact with the excitable tissues. Sooner or later, however, as we should expect, in 
the normal sea-water the rhythmic movements entirely cease, and the bell becomes 
quiescent, with a normal irritability as regards single stimuli. If it be now again 
transferred to the acidulated water, after a short interval the rhythmic movements 
will again commence—and so on during several repetitions of this experiment, until 
the irritability of the tissues has finally become destroyed by the influence of the acid. 
Other chemical irritants which I have tried produce substantially similar effects on 
the paralyzed bells of Sarsia. I shall therefore only wait to describe the influence of 
one of these irritants, the action of which in some respects differs from that of acids, 
and which I have found to be one of the most unfailing in its power to produce the 
rhythmic movements in question. This irritant is glycerine, and in order to produce 
its full effect it requires to be added to the sea-water in about the proportion of 5 per 
cent. The manifestation of artificial rhythm in solutions of this kind is quite unfailing. 
It begins after an exposure of from 15 to 30 seconds, and continues for a variable 
number of seconds. It generally begins with powerful contractions, of a less shivering 
character than those which are produced by acids, and therefore still more closely 
resembling the normal swimming motions of the unmutilated animal. Sometimes, 
however, the first manifestation of the artificial rhythm is in the form of a few gentle 
rhythmic contractions, to be followed by a few seconds of quiescence, and then by the 
commencement of the sustained bout of strong contractions. In either case, when the 
bout of strong contractions sets in, the rate of the rhythm becomes progressively and 
rapidly increased, until in a few seconds it runs up into incipient tetanus. The rate of 
the rhythm still quickening, the tetanus rapidly becomes more and more pronounced, 
till at last the bell becomes quiescent in tonic spasm.* 
If the bell is still left in the glycerine solution nothing further happens ; the tissues 
* Sometimes, however, the order of events is slightly diffei’ent, the advent of the spasm being more 
sudden, and followed by a mitigation of its severity, the bell then exhibiting what is more usually the 
first phase of the series—namely, the occurrence of the locomotor-like contractions Occasionally, also, 
rhythmical shivering contractions may be seen superimposed on the general tonic contraction, either in a 
part or over the whole of the contractile tissues. 
