282 PROFESSOR MARSHALL. 



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, as 

 already noticed, immediate and very active flexion of all the arms, so 

 as to close in over the disc. 



The epithelium of the ambulacral grooves is extremely sensitive, 

 and the results of stimulation are very definite. The slightest irritation 

 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 stimulation be continued 

 the arm is actively flexed and the adjacent arms applied to it, and 

 rubbed along the affected part, as though to remove the source of 

 irritation. Finally, irritation of the ventral surface of the disc between 

 the ambulacral grooves causes movements of the arms, but not nearly 

 so active as when the oral pinnules are touched. 



Experiment 11. — An active specimen was eviscerated, and left for 

 half an hour. The calyx, arms, and pinnules were then successively 

 stimulated, as in the preceding experiment. The results were exactly 

 the same, showing that the communication between the sensitive 

 surface of any part of the calyx, arms, or pinnules, and the motor 

 mechanism of all the arms, is placed elsewhere than in the visceral 

 mass. 



Experiment 12. — An active specimen was taken, and all the soft 

 parts scraped away with a knife from the ventral surface of one of the 

 arms, the scraped portion being about a quarter of an inch in length 

 and one inch from the disc. The pinnules were immediately folded 

 closely alongside the wound, and the animal on being released swam 

 actively in a direction away from the injured arm. It soon came to 

 rest in the normal position, and about six minutes after the operation 

 the distal end of the injured arm was nipped with the forceps. The 

 distal part of the arm, beyond the injury, was at once flexed actively, 

 the proximal part less actively, and the other arms did not move. 

 After a twenty minutes' interval the distal end of the injured arm was 

 again nipped, when active movement of all the arms at once resulted, 

 the animal moving rapidly away from the source of irritation. 



The above experiment shows that the communication between the 

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

 all the arms is not effected by the subepithelial band. The practically 



