674 
ME, Gr. J. EOMANES ON THE LOCOMOTOE SYSTEM OE MEDUSAE. 
is in others. The following series of observations will serve to render a good idea of 
this effect : — 
An Aurelia manifested a regular and sustained rhythm of 36. Immediately after the 
removal of the polypite the rate of rhythm in successive minutes was as follows : — 40, 
39, 37, 35, 32, 30, 29, 26, 24, 18, 14 (40 seconds’ pause), 16, 15, 14, 15, 16 (40 seconds’ 
pause), 22, 20, 19, 15, 16, 17, 14, 13, 13, 15, 16, 16, 17, 18, 14, 12, 13, 11, 12, 9, 15, 16, 
14, 12, 9, &c., the rhythm now continuing very irregular. An hour after the operation 
the following were the number of contractions given in one-minute intervals, the obser- 
vations being taken at intervals of ten minutes : — 15, 15, 12, 22, 14, &c. 
In this experiment, therefore, as soon as the acceleration-stage had been passed, viz. 
about a quarter of an hour after the operation, a great disturbance was observable in 
regularity of the rhythm ; for before the removal of the polypite the Medusa had been 
swimming for hours with perfect regularity. 
It is an important point in connexion with these observations to ascertain whether the 
remarkable effects of mutilation on the rhythm are transitory or permanent ; but as yet 
I have not been able to determine this point with certainty. So far as my observations 
have gone, they all tend to prove that the slowing-effect of the mutilation is permanent ; 
but I do not like as yet to say positively that it is so, because even unmutilated speci- 
mens of Aurelia sometimes slow their rhythm from day to day when kept in confine- 
ment. I may here state, for the benefit of those who may repeat these experiments, 
that when an Aurelia is converted into an open ring, the various parts of the ring fall 
together, especially if it be a narrow one. This unnatural state of things, in conse- 
quence of the irritation arising from the different parts of the ring rubbing on one 
another, causes the remnant of the animal to quicken its swimming-motions. Nor 
is this source of fallacy obviated by keeping the open ring distended by means of 
some cylindrical body of appropriate diameter ; for the presence of this foreign body 
acts more or less as a constant stimulus. The best plan, therefore, to adopt is to make 
the circular incisions only through the thickness of the very tenuous nervo-muscular 
sheet, leaving the gelatinous tissue everywhere intact. The natural shape of the animal 
is thus not in the least affected, while the constituent parts of the nervo-muscular sheet 
are physiologically separated from one another as effectually as if the one were alto- 
gether removed from the other. 
Before concluding my description of these experiments, it may perhaps be as well to 
mention one other, which was designed to meet a possible objection to the inferences 
which, as I shall presently explain, these experiments seem to sustain. It occurred to 
me, as a remote possibility, that the slowing and irregularity of the rhythm, which are 
observable about a quarter of an hour after the operations described, might be due to 
the deprivation of adequate nourishment suffered by the ganglia, in consequence of the 
escape of nutrient matter from the cut ends of the nutrient tubes. Accordingly, instead 
of cutting off the polypite, I tried the effect of momentarily immersing it in hot 
