ME. Gr. J. EOMANES ON THE LOCOMOTOE SYSTEM OF MEDUSAE. 
689 
traction exerts a beneficial influence on its successor, analogous to that which occurs 
in the case of contractions that are due to artificial stimuli. Now both these ques- 
tions admit of being answered by experiments on the Medusae much more satisfac- 
torily than they do by experiments on the heart — if, indeed, it is possible to answer 
them in the latter case at all. To answer the first of these questions, therefore, I built 
up a staircase in the ordinary way, and then suddenly transferred the electrodes to the 
opposite side of the disk from that on which they rested while constructing the staircase. 
On now throwing in another shock at this part of the contractile tissue so remote 
from the part previously irritated, the response resembled in all respects the one 
previously given, i. e. it was a maximum response. Similarly, if the electrodes were 
transferred in the way just described, not after the maximum effect had been attained, 
but at any point during the process of constructing a staircase, the response given to 
the next shock was of an intensity to make it rank as the next step in the staircase. 
Hence, shifting the position of the electrodes in no wise modifies the peculiar effect we 
are considering ; and this fact conclusively proves that the effect is a general one per- 
vading the whole mass of the contractile tissue, and not confined to the locality which 
is the immediate seat of stimulation. Nevertheless this fact does not tend to prove that 
the staircase-effect depends on the process of contraction as distinguished from the process 
of stimulation, because the wave of the former process must always precede that of the 
latter. But, on the other hand, in this connexion it is of the first importance to remember 
a fact recently stated, viz. that a current which at the beginning of a series of stimu- 
lations is of slightly less than minimal intensity, presently becomes of minimal, and 
eventually of much more than minimal intensity — a staircase being thus built up of 
which the first observable step (or contraction) only occurs in response to the second, 
third, or even fourth shock of the series. This fact, of course, clearly tends to show, 
or rather conclusively proves, that the staircase effect, at any rate at its commencement, 
depends on the process of stimulation as distinguished from that of contraction ; for it 
is obvious that the latter process cannot play any part in thus constructing what we 
may term the invisible steps of a staircase. 
To answer the second of the above questions, I placed an Aurelia with its concave 
surface uppermost, and removed seven of its lithocysts ; I then observed the spontaneous 
discharge of the remaining one, and found it to be conspicuous enough — that after the 
occurrence of one of the natural pauses (if this were of sufficient duration) the first 
contraction was feeble, the next stronger, the next still stronger, and so on, till the 
maximum was attained. This natural staircase action admits of being very prettily 
shown in another way. If a tolerably large Aurelia is cut into a spiral strip of small 
width and great length, and if all the lithocysts are removed except one at one end of 
the strip, it may be observed that, after the occurrence of a natural pause, the first 
discharge only penetrates perhaps about a quarter of the length of the strip, the next 
discharge penetrates a little further, the next further, and so on, till finally the con- 
tractile waves pass from end to end. On now removing the ganglion, waiting a few 
