STAR-FISH AND SEA-URCHINS. 303 
spines and pedicellarize depend for their function of 
localizing and closing 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 
such 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 seizing 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 
organs of both hemispheres (these operations pro- 
