532 A. MILNES MARSHALL. 



of the affected part and for a quarter of an incli on either side 

 of the wound were cut away to prevent any possibility of con- 

 tact communication between the parts on either side of the 

 injury. The injured part was then painted all round very freely 

 with strong nitric acidj 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 one of 

 the pair stretched straight out horizontally, and the other 

 arms rather strongly extended. After a few minutes it began 

 to move slowly^ and in six 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. 



The above experiment, which was repeated several times, both 

 on entire and on eviscerated specimens, proves conclusively that 

 the communication between the distal end of the irritated arm 

 and the motor mechanism of the arms is effected by the axial 

 cord; in other words, that the axial cord plays the part of an 

 afferent or sensory nerve, conveying impulses centripetally. 

 Furthermore, that it is the normal path of communication of 

 such impulses is, I think, evident from the response to stimula- 

 tion being as ready when it alone remains as in the uninjured 

 animal. It remains, however, to show whether it is the only 

 path of communication. To test this I attempted several 

 times to divide the axial cord between two of the segments by 

 a fine scalpel, but I failed, as Dr. Carpenter had done previously, 

 owing to the fact that as soon as the knife reached the axial 

 cord the arm was at once thrown off, usually at a point two or 

 three segments nearer the disc than the injury. I then tried 

 the plan adopted by Dr. Carpenter/ i. e. burning away the 

 dorsal half of the arm with nitric acid so as to expose and 

 divide the axial cord, and with the following results. 

 ' Carpenter, ' Proc. Royal Soc./ 1876, p. 654. 



