MR. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSAE. 
733 
before any of their number is again able to originate a discharge will be the same as if 
their physiological harmony had never been destroyed*. 
In view of these considerations I tried the following experiments. Instead of 
beginning the radial cuts from the margin, I began them from the apex of the cone ; 
and I found that however many of such cuts I introduced, and however far down the 
cone I carried them, so long as I did not actually sever the margin so long did all the 
divisions of the bell continue to contract simultaneously^. This fact therefore proves 
at least this much, that whether or not in the previous experiments true ganglionic 
coordination was effected through the upper zones of the bell, the margin of the bell is 
alone sufficient to maintain such coordination. 
The next experiment I tried was to make four short radial incisions in the margin as 
before described, and then to continue one of these incisions the whole way up the bell. 
By careful observation I could now perceive that all the marginal ganglia did not 
discharge simultaneously ; for when those situated nearest to the long radial cut 
happened to take the initiative, the resulting contractile wave, having double the 
distance to travel which it would have had if the long radial cut had been absent 
(or, as in the experiment described at the beginning of this subsection (b), if this radial 
cut had only been of the same length as the other three radial cuts), could now be fol- 
lowed by the eye in its very rapid course round the bell. Now the fact that in this 
form of section I was able to detect the passage of a wave, proves that the three short 
radial sections had destroyed the coordinated action of the marginal ganglia. 
From these experiments, then, I conclude that in this genus ganglionic coordination, 
in the strict sense of the term, is effected exclusively by means of the marginal nerves. 
And as these experiments on Sarsia are exceedingly difficult to conduct, owing to the 
very rapid passage of contractile waves, it is satisfactory to find that this conclusion is 
further supported by the analogy which the other species of a naked-eyed Medusa 
afford, and to the consideration of which we shall now proceed. 
( c ) The effects of four short radial incisions through the margin of any species of 
Tiaropsis, Thaumantias , Staurophora, &c. are usually very conspicuous. Each of the 
quadrants included between two adjacent incisions shows a strong tendency to assume 
an independent action of its own. This tendency is sometimes so pronounced as to 
amount almost to a total destruction of contractional continuity between two or more 
quadrants of the bell ; but more usually the effect of the marginal sections is merely 
that of destroying excitational continuity, or at least physiological harmony. In vigorous 
* As in the last section, I adhere in the text to the current theory of ganglionic action ; hut the above con- 
siderations apply equally well on the new theory. These considerations are the same as have already been 
employed in an abridged form with reference to Aurelia, at the beginning of the last section. 
t This could be particularly well seen if, after the extreme apex of the cone had been removed, one of the 
four radial cuts was continued through the margin, and the latter was then spread out into a linear form by 
gently pressing the animal against the flat side of the glass vessel in which it was contained. The same ex- 
periment performed on Aurelia is, of course, attended with a totally different result, now one segment and now 
another originating a discharge which then spreads to all the others in the form of a contractile wave. 
5x2 
