700 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



portion being about a quarter of an inch in length and 1 inch from the disk. 

 The pinnules were immediately folded closely alongside the wound, and the 

 animal on being released swam actively away from the injured arm. It soon 

 came to rest in the normal position, and about 6 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 20 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. 



Experiment 13. A large and vigorous specimen was taken and a quarter of 

 an inch of one of the arms, about an inch from the base, thoroughly scraped with 

 a scalpel all around so as to remove the soft parts as completely as possible. 

 The pinnules of the affected part and for a quarter of an inch on either side of 

 the wound were cut away to prevent any possibility of contact communication 

 between the parts on either side of the injury. The injured part was then painted all 

 around very freely with strong nitric acid, the operation being repeated until fully 

 half the thickness of the calcareous segments had been dissolved away. The 

 wound was then washed freely with sea water and the animal returned to the 

 tank. It fell at once to the bottom on its side with the injured arm and the 

 other arm of the same pair stretched out horizontally, and the other arms rather 

 strongly extended. After a few minutes it began to move slowly, and in 6 minutes 

 had completely resumed the normal position. After half an hour's interval the 

 distal end of the injured arm was sharply nipped with forceps, when strong 

 active movements of all the arms at once resulted, the animal moving rapidly 

 away from the source of irritation. 



Experiment 14- An active specimen was removed from the water, the dorsal 

 surface of one of the arms carefully dried, and strong nitric acid applied with 

 a fine brush to the dorsal surface of the fourth and fifth brachials, which were 

 dissolved away until the axial cord was exposed and destroyed. If the arm were 

 held during the operation it was usually thrown off, but if the disk only were held 

 and the arm allowed merely to rest on the fingers the operation was always 

 successful. The animal was then returned to the water, where it assumed almost 

 at once the normal position. After half an hour's rest the distal end of the 

 injured arm was nipped sharply with forceps; active movements of the irritated 

 arm beyond the injury ensued, but no movement whatever of either the proximal 

 part of the injured arm or of any of the other arms. 



When in this experiment the ambulacral epithelium is left absolutely unin- 

 jured it responds to stimulation in a perfectly normal manner. 



Experiment IB. One of the arms of an active specimen was cut across at 

 about its middle and the animal held in the tank so that the stump of the ampu- 

 tated arm was just above the surface of the water. The stump was carefully 

 dried and the axial cord touched with a fine needle or with a finely pointed brush 

 charged with nitric acid. Very violent movements of all the arms at once resulted. 



