334 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



causes instantaneous movement of the four or five pairs of pinnules immediately 

 adjacent to the irritated spot, the pinnules being folded alongside the ambulacral 

 groove so as to close it in and grasp the needle or other source of irritation. If 

 the stimulus be continued the .arm is actively flexed and the adjacent arms applied 

 to it as though to remove the source of irritation. The communication between 

 the sensitive surface of an arm or pinnule and the motor mechanism of all the 

 arms is not effected by the epithelial band, and is not affected by its destruc- 

 tion. Experiments yield identical results in eviscerated and unmutilated indi- 

 viduals. Marshall believes that the epithelial nerves form a special part of the 

 nervous system connected with the ambulacral epithelium and the water vessels. 



Irritation of a pinnule causes, according to the degree and duration of the 

 stimulation, movement of the pinnule, movement of the whole arm, approximation 

 of the adjacent arms to the affected one, or active movement of the whole animal 

 away from the source of irritation. 



Irritation of the oral pinnules causes immediate and very active flexion of 

 all the arms, resulting in closing them in over the disk. 



Irritation of the central organ, whether mechanical or chemical, causes strong 

 flexion of all the arms, which persists as long as the stimulation is continued. 

 Dr. W. B. Carpenter found that sudden and consentaneous flexion of the arms 

 follows irritation of the central organ from the oral surface, while Professor 

 Marshall found that swimming movements quite as often result. The latter 

 believes that the slight difference may be accounted for by the oral pinnules being 

 accidentally irritated in some of the experiments, for if these be clipped off 

 swimming movements of the arms almost invariably follow irritation of the central 

 capsule from above. 



Mechanical or chemical stimulation of the axial cord in the stump of an 

 amputated arm causes violent and repeated flexion of all the arms; stimulation 

 applied to other parts of the cut end produce but very little effect. Destruction 

 of the axial cord causes the arm beyond that point to coil spirally and to remain 

 so coiled regardless of the movements of the rest of the arm or of the animal. 

 Stimulation of the distal portion of an arm in which the axial cord has been 

 destroyed causes active movements of the irritated arm as far as the injury, but 

 no movement whatever either of the proximal portion of the injured arm or of any 

 of the other arms. The epithelial nerves under the ambulacral grooves, however, 

 continue to respond to stimuli in a perfectly normal manner. If the axial cord 

 be divided in two places, stimulation between the two wounds causes movements 

 of that part of the arm only. 



Thus the axial cord furnishes the sole afferent communication, as well as 

 the sole motor communication, between the arms and the central organ, and 

 between different parts of the same arm. Destruction for some distance of the 

 soft parts of the ventral surface of an arm does not affect, either in eviscerated 

 or in unmutilated individuals, the movements of the animal on either side of the 

 destroyed portion. 



The central organ is in direct physiological communication with the muscles 

 of the arms, and experiments yield identical results whether performed on evis- 



