286 PROFESSOR MARSHALL. 



The two preceding experiments show that division of the axial cord 

 destroys the motor communication between the parts on either side of 

 the section as completely as we have already found it to destroy the 

 afferent or sensory communication. When combined with Experiment 

 1 6, which shows that the motor communication is not effected by any 

 other of the soft parts, the inference is irresistible that the sole motor 

 communication is that afforded by the axial cords. One additional 

 experiment may be mentioned in support of this conclusion. 



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. 



It still remains to inquire into the functions of the commissural 

 bands which connect the axial cords together, for if the axial cords 

 are really nerves these connecting bands, which are identical with 

 them in histological structure, must be nerves also, and experiment 

 ought to throw light on their purpose. These commissures are of two 

 kinds (cf. fig. 3) : there is, firstly, the great pentagonal commissure in 

 the First Radials which connect together the roots of the radial cords; 

 and, secondly, we have in each Third Radial a rather complicated 

 connection, by means of a transverse commissure and a chiasma, 

 between the two axial cords into which each radial cord divides. I 

 propose to deal with these two sets of fibres separately, taking the 

 great pentagonal commissure first. 



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 (cf. fig. 1). 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. 



This experiment shows that the central capsule does not form the 

 sole physiological connection between the axial cords (nerves) of the 



