MONOGRAPH OF THE EXISTING CKINOIDS. 701 



Similar stimulation of the ambulacral epithelium or of other parts of the section 

 produced only very slight and local movements. 



Experiment 16. As in experiment 12 the soft parts were scraped away from 

 the ventral surface of about a quarter of an inch of one of the arms an inch 

 from the base. On being returned to the water the animal swam actively, all 

 the arms moving vigorously and normally, including the injured one, which, 

 however, was rather less active than the others, and a little stiff at the scraped 

 part, probably from direct injury to the muscles. 



Experiment 17. The operation was the same as in experiment 14, the dorsal 

 half of one of the arms about an inch from the disk being dissolved away by 

 nitric acid until the axial cord was exposed and divided. The animal was then 

 returned to the water, where it remained quiescent for a few seconds and then 

 commenced to swim actively and spontaneously, all the arms moving perfectly 

 normally except the injured one, the proximal end of which moved slightly while 

 the distal part beyond the injury was perfectly motionless and flexed spirally 

 into a coil. After a short time the animal came to rest in a perfectly normal 

 position, but for the spiral coiling of the distal part of the injured arm, which 

 persisted. After a quarter of an hour's rest one of the uninjured arms was irri- 

 tated, causing at once active movements of the uninjured arms and of the proximal 

 part of the injured arm, but none whatever of its distal part. 



Experiment 18. In a fresh specimen two injuries, similar to that in experi- 

 ment 17, were made in one of the arms at spots about an inch and a half apart. 

 Stimulation of the arm itself, or of the pinnules, between the two wounds caused 

 movements of the middle portion of the arm but none whatever of the proximal 

 or distal portions. 



Experiment 19. One of the arms of a vigorous specimen was amputated by 

 a snip of the scissors. The detached arm exhibited extremely active movements 

 for about a quarter of an hour, coiling and uncoiling with great force and rapidity. 

 After a time it became quiescent. It was then held in the tank with the proximal 

 end just out of water. The end was carefully dried and the exposed section of the 

 axial cord touched with a needle and a fine brush charged with nitric acid. The 

 slightest irritation, whether mechanical or chemical, caused violent and repeated 

 flexion of the arm. Stimulation applied to other parts of the cut end produced 

 but very little effect. 



Experiment 20. A specimen was eviscerated and a needle passed down from 

 the oral surface into the chambered organ and worked about so as to destroy as 

 completely as possible the central capsule and chambered organ. The animal 

 was then returned to the water and left at rest for half an hour. One of the 

 arms was then suddenly nipped with forceps, when all the arms exhibited active 

 movement, though the animal did not attempt to swim. 



Experiment 21. The same specimen was taken and the inside of the canal 

 lying within the radials was freely painted with nitric acid until the pentagonal 

 commissure was exposed and destroyed. The animal was then returned to the 

 water and left for half an hour on its oral face, where it remained without any 



