708 
ME. Gf. J. EOMANES ON THE LOCOMOTOE SYSTEM OE MEDUSiE. 
of unsevered tissue on either side of that tube. The fact of its doing so, however, 
certainly seems to be connected with the fact of the radial tubes being tracts of high 
excitability. Now the latter fact, it seems to me, can only be accounted for in one of two 
ways. Either (a) we must suppose the course of a radial tube to coincide with that of 
a chain of ganglionic elements, or else ( b ) we must suppose it to coincide with something 
resembling a nerve-trunk — the latter being composed of aggregations of the afferent 
lines which w T e have already supposed to constitute the rudimentary nerve-plexus. 
According to the first of these suppositions, the comparatively high excitability of the 
radial tubes, as well as the pointing of the polypite to the unsevered tube in a specimen 
prepared as represented in fig. 8, would both be explained by the further supposition 
that when such a ganglion chain is stimulated — either directly or by conduction of the 
stimulus from a distance — the ganglionic elements discharge their influence, and so add 
to the strength of the original stimulus. According to the second of the above suppo- 
sitions (viz. b), the fact of the high excitability of the nutrient tubes would be explained 
by the consideration that a stimulus applied to the supposed nerve-trunk would directly 
affect a greater number of the plexus-elements than would a stimulus applied to any 
other part of the bell. The additional fact to be met, viz. the pointing of the polypite 
to a single unsevered tube, is not quite so easy to explain on the present supposition; 
for if the assumed nerve-trunk is identical in function with a true nerve-trunk, the 
afferent elements collected in it ought to communicate to the polypite the impression of 
having had their distal terminations irritated ; and therefore the fact of a number of 
such elements being collected into a single trunk ought not to cause the polypite to refer 
a distant seat of irritation to that trunk rather than to any of the parts from which the 
plexus-elements may emanate. Concerning this difficulty, however, I may observe that 
we seem to have in it one of those cases in which it would be very unsafe to argue with 
any confidence from the highly integrated nervous systems with which we are best 
acquainted to the primitive nervous systems with which we are now concerned. And 
although it would occupy too much space to enter into a discussion of this subject, I 
may further observe that I think it is not at all improbable that the polypite of Tia- 
ropsis indicans should, in the absence of more definite information, refer a distant seat 
of injury to that tract of collected afferent elements through which it actually receives 
the strongest stimulation. 
The first of these two suppositions (viz. a) will be found to derive some little support 
when we come to consider a curious class of facts to he dealt with in the next section. 
The second of these suppositions (viz. b) is supported by the histological researches of 
Professor Haeckel on Geryonia , a genus which closely resembles Tiaropsis indicans in 
form. This observer describes nerve-filaments following everywhere the course of the 
radial tubes, and receiving a number of minute filaments from either side. Moreover, 
the supposition we are now considering is further analogically supported by Schultze’s 
researches as to structure, and my own as to function, of the radial nerve-tracts in 
Sarsia. 
