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ME. G. J. EOMANES ON THE LOCOMOTOE SYSTEM OF MEDHS2E. 
bodies in the same way, and the polypite still contracted when I irritated any one of 
the four tentacles. 
Now, as these experiments were repeated on a number of specimens — the radial tubes 
being in some cases divided at the base and in others at the apex of the cone — and as 
the experiments always yielded the same result, I cannot doubt that the nervous con- 
nexions between the margin and the polypite are in no wise restricted to the course of 
the nutrient tubes. 
(D) Nervous connexion between the Nectocalyx and the Polypite of Sarsia. — The 
polypite of Sarsia often shows itself more sensitive than does the nectocalyx to stimuli 
applied to the latter. Moreover, as already stated, the polypite of Sarsia is much more 
sensitive to stimuli applied to a tentacle or to a marginal body of the nectocalyx than 
to stimuli applied at any other part of that organ. As regards the general surface of 
the irritable tissue of the nectocalyx, the polypite is more sensitive to stimuli applied at 
some parts than it is to stimuli applied at other parts ; but in different specimens there is 
no constancy as to the position occupied by these excitable tracts. 1 think, however, 
that, as a general rule, stimulation of the parts of the bell nearest to the insertion of 
the polypite causes the latter to respond more readily than does stimulation of the parts 
more distant. Over all parts of the bell, however, during such explorations, sudden 
variations in the responses of the polypite are observable according as the electrodes 
are shifted a millimetre or less one way or the other ; in some cases, indeed, even a few 
hair-breadths will make all the difference between an active response and no response. 
Similarly with mechanical stimulation. 
From these explorations, therefore, it would seem that the polypite of Sarsia is in very 
intimate communication with the nectocalyx, and especially with the marginal bodies, 
by means of a nervous plexus pervading the excitable tissues of the latter, but that the 
principal nervous tracts by which this communication is effected are not constant as to 
their position in different individuals. 
(E) Character of the Excitable Tissues of Sarsia. — It will be remembered that in my 
former paper I described several experiments which were designed to test the amount 
of section that the excitable tissues of the Medusse would tolerate without suffering loss 
of their “physiological continuity.” This term, as previously used by Dr. Foster, 
implies such a condition of excitable tissue that its various parts are in physiological 
connexion with one another, whether by means of contractile elements (protoplasm, 
muscle) or conductile elements (“ lines of discharge,” nerves). Therefore, in my last 
paper, I employed this term to designate such a condition on the part of contractile 
tissues as admits of an uninterrupted passage along their substance of what I called 
“ contractile waves.” But having in the present paper an important distinction to draw, 
I must discard the generic term “physiological continuity,” and substitute for it two 
specific terms, viz. “ contractional continuity ” and “ excitational continuity.” By “ con- 
tractional continuity ” I shall wish to be understood such a condition of contractile tissue 
as admits of the uninterrupted passage of contractile waves ; while by “ excitational con- 
tinuity ” I shall wish to be understood such a condition of the contractile tissues as 
