276 
MR. a. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSA. 
interval of time ; so that one cannot be quite sure, even for an hour after the operation, 
that the paralysis, however complete up to that time, will prove itself permanent. 
In the cases composing the other of these subdivisions, the paralysis, besides being 
instantaneous and complete, is also permanent, and thus in every way resembles the 
paralysis caused by the fundamental experiment in the case of nectocalyces. 
Excision of the entire margin of Cyancea capillata causes, in the majority of cases, 
instantaneous and complete paralysis of the gonocalyx ; but this result is not of such 
comparatively frequent occurrence as it is with Aurelia aurita. Moreover, in the cases 
where supernumerary centres do not assert themselves immediately after the operation, 
they are almost sure to do so if the mutilated gonocalyx be left sufficiently long to 
recover from the shock caused by the operation. The period required before the first 
spontaneous contraction is given in such cases varies from a few minutes to an hour or 
more ; but it is observable that if this period be prolonged, the subsequent contractions 
are almost stire to be of a feeble character with immensely long intervals between 
their occurrence — perhaps only one contraction being given in ten minutes or more, 
instead of between twenty to thirty contractions in one minute, as is characteristic 
of the unmutilated animal. 
Upon the whole, then, although in all the species of covered-eyed Medusae which I have 
as yet had the opportunity of examining the effects which result 
from excising the margins of gonocalyces are such as to warrant 
me in saying that the main supply of locomotor centres appears 
to be usually situated in that part of these organs, these effects 
are nevertheless such as to compel me at the same time to con- 
clude that the locomotor centres of the covered-eyed Medusae are 
more diffused or segregated than are those of the naked-eyed 
Medusae. Lastly, it should be stated that all the species of covered- 
eyed Medusae resemble all the species of naked-eyed Medusae in 
that their members will endure any amount of section it is possible 
to make upon any of their parts, other than their margins, with- 
out their spontaneity being in the smallest degree affected. 
§ 3. The effects of excising certain portions of the margins 
of Nectocalyces . — The next question which naturally presents itself 
is as to whether the locomotor centres are equally distributed 
all round the margin of a swimming-organ, or situated only, or 
chiefly, in the so-called marginal bodies. To take the case 
of the naked-eyed Medusae first, it is evident that in most of 
the genera, in consequence of the intertentacular spaces being 
so small, it is impossible to cut out the marginal bodies with- 
out at the same time cutting out the intervening portions of 
the margin. The genus Sarsia, however, is admirably adapted 
(as a glance at the annexed figure will show) for trying the effects of removing the 
Fig. 1. 
Sarsia, x 3 times. 
