690 
ME. G. J. EOMANES ON THE LOCOMOTOE SYSTEM OF MEDUSAE. 
minutes, and then stimulating with successive induction-shocks, the same progressive 
penetration is observable as that which previously took place with the ganglionic 
stimulation. Lastly, the identity of natural and artificial staircase action may be placed 
beyond all doubt by an experiment in which the effects of induction-shocks and of 
ganglionic discharges are combined. To accomplish this, all the lithocysts save one 
are removed, and a staircase is then built up in the ordinary way by successive induction- 
shocks. It will now occasionally happen that the ganglion originates a discharge 
during the process of constructing the staircase ; and when this does happen, it may 
invariably be observed that the contraction due to the natural stimulus is just of the 
proper intensity to take its place in the staircase which is being built up by the artificial 
stimuli, and this at whatever point the natural contraction happens to come in*. 
Of course, in all these experiments with natural discharges, care must be taken to 
choose a lithocyst of a potency adapted to the object in view. This condition, before it 
is satisfied, often requires a number of trials to be made. The experiment with the 
spiral strip may prove particularly tedious in this respect, as it is difficult to obtain 
such a strip presenting the proper degree of resistance in relation to the terminal 
ganglion j\ 
* I may here observe that if an Aurelia with all its lithocysts removed happens, during the construction of 
a staircase hy stimuli, to give a spontaneous contraction, this also ranks as the nest step in the staircase, just 
in the same way as does a spontaneous contraction proceeding from a single remaining lithocyst. This proves 
that “ secondary contractions ” are not really, as Dr. Eimek describes them, more “ feeble and inefficient ” than 
primary ones; and that the only reason why they usually appear to be so is because they usually occur singly 
with a long interval between them, so that each secondary contraction usually corresponds with the first step 
of a staircase. But when, as sometimes happens, two or three secondary contractions follow one another at 
the rate observable in ordinary swimming, the second contraction is stronger than the first, and the third than 
the second, and so on, just as in the construction of a staircase hy a single remaining lithocyst after the occur- 
rence of a natural pause of adequate duration. It is almost needless to state that, as this effect of the summation 
of stimuli had not been observed at the time when Dr. Eimek published his paper, he is not to be accused of any 
inaccuracy in his observations because he described the “ secondary contractions ” as “ feeble and inefficient.” 
t [As the present communication was originally accepted by the Eoyal Society, there here followed a 
lengthy subsection on “ Artificial Ehythm.” A condensed epitome of the main facts which were detailed in 
that subsection may he found in the already published abstract of this paper in the Proceedings of the Eoyal 
Society. But as the new theory of ganglionic action which it is the main object of this passage to disclose 
appears to me a theory of sufficient importance to demand its final publication in as complete a form as possible, 
I have sought and obtained the permission of the Eoyal Society to withdraw this subsection from the proof. 
And, as a further reason for postponing publication of the passage on “Artificial Ehythm,” I may state that, as 
this paper is of undue length, it seemed to me desirable, if possible, to relegate a portion of it to my next paper ; 
and I find that this subsection is the most suitable part temporarily to suppress, because the facts of which it 
treats form in themselves a connected body distinct from all the other facts which are detailed in the rest of 
this communication ; so that while their omission from the present paper does not entail any further modifica- 
tion of the latter, they will admit of being introduced en masse in my next paper. When, therefore, I shall 
have completed the further experiments which in this connexion I have devised, I shall hope to communicate 
to the Eoyal Society, in a single connected series, all the facts and inferences which bear upon this subject. — 
1878 .] 
