122 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
for it is evident that, according to the hypothesis, 
the radial fibres occupying such a band are the only 
ones whose irritation the manubrium is able to 
perceive, and hence it is to be expected that it 
should tend to refer to these particular fibres a 
source of irritation occurring anywhere in the 
mutilated bell. 
It is not quite so easy to understand why, in the 
last-mentioned experiment, the manubrium should 
tend to refer a seat of irritation to the unsevered 
nutrient tube, or nerve-trunk, rather than to the 
unsevered nerves in the general nerve-plexus on 
either side of that nerve-trunk; for if this nerve- 
trunk at all resembles in its functions the nerve- 
trunks of higher animals, the afferent elements 
collected in it ought to communicate to the manu- 
brium 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 manubrium 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 un- 
safe 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 dis- 
cussion of this subject, I may further observe that 
I think it is not at all improbable that the manu- 
