MR. a. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUS2E. 
707 
to reach the polypite after being diffused through many or all of the other radial lines 
(such stimuli thus converging from many directions), are responded to when they reach 
the polypite, not by any decided localizing action on the part of the latter, but, as the 
hypothesis would lead us to expect, by the tentative and apparently random motions which 
are actually observed. Moreover, we must not neglect to notice that these tentative or 
random movements resemble in every way the localizing movements, save only in their 
want of precision. Again, this hypothesis is rendered yet more probable by the occur- 
rence of those gradations in the localizing power of the polypite which we have seen to 
be so well marked under certain conditions. The occurrence of such gradations under 
the conditions I have named is what the plexus theory would lead us to expect, because 
the closer beneath a section that a stimulus is applied, the greater will be the lateral 
spread of the stimulus through the plexus before it reaches the polypite. Similarly, 
the further the circumferential distance from the nearest end of such a section that the 
stimulus is applied, the greater will be its lateral spread before reaching the polypite. 
Lastly, the present hypothesis would further lead us to anticipate the fact that when 
Tiaropsis indicans is prepared as represented in fig. 8, the polypite refers a stimulus 
applied anywhere in the mutilated nectocalyx to the band of tissue by which it is still 
left in connexion with that organ ; for it is evident that, according to the hypothesis, the 
radial lines occupying such a band are the only ones whose irritation the polypite is able 
to perceive ; and hence it is to be expected that it should tend to refer to these particular 
lines a source of irritation occurring anywhere in the mutilated bell*. 
It is not quite so clear why, in. the last-mentioned experiment, the polypite should 
tend to refer a seat of irritation to the unsevered nutrient tube, rather than to the tracts 
* It may be objected tbat the fact of diffused excitability persisting after destruction of the localizing function 
does not prove tbat the same tissue-elements are concerned in the two cases. For instance, in fig. 1, Plate 30, 
before introducing the cut a, a stimulus applied at b would, as before stated, cause localizing motion of the 
polypite. Let us call the tissue-tracts by which this localizing motion is effected x x, and let us call all the 
other tracts belonging to the same system, but occurring in other parts of the bell, x' x'. Now the hypothesis 
above explained supposes that after the cut a has been introduced, the random motions of the polypite which 
ensue on stimulating b are due to an escape of the stimulus at a from x x to x' x\ i. e. all over the bell. But 
the objector may ask, Why not suppose that the stimulus is conveyed to the polypite by some other tissue-element 
altogether, e. g. by z z, and hence that the function of the radial elements x x is exclusively that of enabling the 
polypite to localize correctly? Against this objection, of course, nothing can be urged, except that it merely 
suggests a possibility, and this a very improbable one. If such additional tissue-tracts are present, they must 
resemble those treated of in the text in at least one distinctive feature, viz. in having the property of conveying 
impressions to a distance. And forasmuch as the only objection to the above hypothesis consists in its suppos- 
ing the distinguishing property of nerve to be blended with the property of vicarious action in a high degree, I 
cannot perceive any advantage in again supposing these properties blended in another tissue-element. On the 
contrary, any such additional supposition appears to me quite unnecessary, and, if accepted, would certainly 
serve but to render the explanation ofEered in the text more complicated than it is. Moreover the fact already 
alluded to in the text — viz. that tentative movements differ in no respect from the accurately localizing move- 
ments, except in their want of precision — this fact, I think, strongly tends to show that the same kind of 
tissue-elements is concerned in the production of all these movements. 
5 G 
MDCCCLXXVII. 
