8 Mr. G. J. Romanes and Prof. J. C. Ewart, [Mar. 24 



logical continuity in the rows of pedicels and the muscular system of the 

 rays, does not destroy, or perceptibly impair, physiological continuity 

 in the external nerve-plexus ; for however much the nerve-ring and 

 nerve- trunks may be injured, stimulation on the dorsal surface of the 

 animal throws all the pedicels and the muscular system of the rays into 

 active movement. This fact proves that the pedicels and the muscles 

 are all held in nervous connexion with one another by the external 

 plexus, without reference to the integrity of the main trunks. 



If a cork-borer be rotated against the external surface of an Echinus 

 till the calcareous substance of the shell is reached, and therefore 

 a continuous circular section of the overlying tissues effected, the 

 spines and pedicellariee within the circular area are physiologically 

 separated from those without it, as regards their local reflex irrita- 

 bility. That is to say, if any part of this circular area is stimulated, 

 all the spines and pedicellarise within that area immediately respond to 

 the stimulation in the ordinary way, while none of the spines or pedi- 

 cellarise surrounding the area are affected, and conversely. Therefore 

 we conclude that the function of the spines and pedicellarias of local- 

 ising and gathering round a seat of stimulation is exclusively dependent 

 upon the external nervous plexus. If the line of injury is not a closed 

 curve, so as not to produce a physiological island, the stimulating 

 influence will radiate in straight lines from its source, but will not 

 irradiate round the ends of the curve or line of injury. 



Although the nervous connexions on which the spines and pedi- 

 cellariaa depend for their function of localising and closing round a 

 seat of stimulation are thus shown to be completely destroyed by 

 injury of the external plexus, other nervous connexions, upon which 

 another function of the spines depends, are not in the smallest degree 

 impaired by such injury. This other function is that which brings 

 about the general co-ordinated action of all the spines for the pur- 

 poses of locomotion. That this function is not impaired by injury of 

 the external plexus is proved by severely stimulating an area within a 

 closed line of injury on the surface of the shell ; all the spines over 

 the whole surface of the animal then manifest their bristling move- 

 ments, and by their co-ordinated action convey the animal in a straight 

 line of escape from the source of irritation. 



We have, therefore, to distinguish between what may be called the 

 local reflex function of the spines, which they show in common with 

 the pedicellariaB and which is exclusively dependent upon the external 

 plexus, and what we may call the universal reflex function of the 

 spines, which consists in their general co-ordinated action for the 

 purposes of locomotion and which is wholly independent of the 

 external plexus. Evidently, therefore, this more universal function 

 must depend upon some other set of nervous connexions (which, 

 however, we have not been able to detect histologically), and experi- 



