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 beincr 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- 



