STAR- FISH AND SEA-URCHINS. 303 



spines and pcdiccllarire depend for their function of 

 localizino- and closino- round a seat of stimulation 

 are thus shown to be completely destroyed by 

 injury of the external plexus, other nervous connec- 

 tions, upon which another function of the spines 

 depends, are not in the smallest degree impaired by 

 Buch injury. The other function to which I allude 

 is that which brings about the general co-ordinated 

 action of all the spines for the purposes of locomo- 

 tion. That this function is not impaired by injury 

 of the external plexus is proved by the fact that 

 if the area within a closed line of injury on the 

 surface of the shell be strongly irritated, all the 

 spines over the whole surface begin to manifest 

 their peculiar bristling movements, and by this co- 

 ordinated action rapidly move the animal in a 

 straight line of escape from the source of irritation ; 

 the injury to the external plexus, although com- 

 pletely separating the spines enclosed by it from 

 their neighbouring spines as regards what may be 

 called their local function of seizinn^ the instrument 

 of stimulation, nevertheless leaves them in undis- 

 turbed connection with all the other spines in the 

 organism as regards what may be called their 

 universal function of locomotion. 



Evidently, therefore, this more universal function 

 must depend upon some other set of nervous con- 

 nections ; and experiment shows that these are dis- 

 tributed over all the internal surface of the shell. 

 Our mode of experimenting was to divide the 

 animal into two hemispheres, remove all the internal 

 oigan« of both hemispheres (these operations pro- 



