ME. G-. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSAE. 
285 
The mode of section is a very simple one, consisting merely in cutting round a greater 
or less extent of the marginal tissue, leaving one end of the resulting strip free and the 
other end attached in situ. Upon now irritating the distal or unattached end of this 
marginal strip, a wave of contraction may invariably be seen to start from the point at 
which the irritation is applied, and with some rapidity to traverse the entire strip. 
Upon arriving at the proximal or attached end of the strip, this contractile wave delivers 
its influence into the swimming-organ, which thereupon contracts in exactly the same 
manner as it does when itself directly irritated. Of course spontaneous contractions 
are continually originating in some portion or other of the severed strip ; and these give 
rise to contractile waves and to contractions of the nectocalyx, just in the same way as 
do the disturbances originated by stimulus. In those species, however, of the disco- 
phorous naked-eyed Medusse which respond to stimulation by the peculiar spasmodic 
movements of the nectocalyx already described, the difference between the effects upon 
the nectocalyx of contractile waves that originate spontaneously in the severed strip 
and those that thus originate in answer to stimuli is of a very marked character ; for 
the spasmodic movements of the nectocalyx are as easily and as certainly evoked by 
irritating any part of the severed strip, as they are by irritating the substance of the 
nectocalyx itself. 
From this description it will easily be seen that a Medusa thus operated upon 
supplies all the essential conditions for conducting the most important part of the 
investigation, so far as electrical stimulation is concerned, viz. that relating to electro- 
tonus. We have already obtained ample evidence to warrant ns in concluding that, 
if the organization of the Medusae presents us with any thing that is analogous to 
nervous tissue at all, the periphery of the swimming-organ must be the position in 
which it is chiefly localized ; so that even if these animals possess but the rudiments of 
a nervous system, a Medusa, when subjected to the mode of section just described, is 
for all practical purposes a nerve-muscle preparation. 
If the intention of the experimenter be merely that of producing contractile waves, 
it does not signify upon what species of Medusa the form of section just described is 
practised; for whatever species happens to be chosen, the experiment's sure to be 
successful. But when the object in view is that of electrotonic investigation, it is 
desirable to exercise the utmost discretion in the choice of a suitable species. The one 
I have found most suitable is Staurophora laciniata ; for this form presents all the 
qualities the experimenter can desire. Its size is sufficient to yield a foot or more of 
marginal tissue whereon to cause and test for electrotonus ; its manner of folding 
together in response to stimulation is most decided ; its endurance is considerable ; and 
its sensitiveness to electrical stimuli is so great, that I have seen it respond to closure 
of the constant current supplied by a single Daniell’s cell when all the plugs of the 
rheochord were firmly pressed in, and the travelling mercury cups were only drawn out 
one quarter of an inch. 
When, therefore, I began my investigation upon this animal, I thought that the 
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