THE NERVOUS SYSTEM OF ANTEDON ROSACEUS. 281 



the stimulation, but the movement was limited to the arm directly 

 irritated, none of the other arms sharing in it, except sometimes the 

 other arm of the pair to which the irritated arm belonged. 



This experiment shows that the physiological connection between 

 the arms can be destroyed by removal of the central capsule and of 

 its branches, including the pentagonal commissure. After this operation 

 the several arms, with the exception of the two of each pair, are 

 physiologically isolated from one another. The experiment yields 

 identical results whether the visceral mass be present or not. 



I have found it very necessary after severe operations to allow 

 sufficient time for recovery from shock before experimenting further, 

 and through failure to observe this precaution I obtained at first several 

 very contradictory and perplexing results. From half an hour to an 

 hour I usually found to be sufficient. 



E. On the Functions of the Axial Cords. 



Experiments on the functions of the axial cords and their branches 

 fall naturally under two heads, i.e. those concerned with the relations 

 of these structures to sensation and to motion respectively. 



I propose to commence with the former of these, though, as it 

 sometimes happens that the same experiment is concerned with both 

 sensation and motion, it will not be advisable to draw too sharp a line 

 between the two divisions. 



Experiment 10. — Various parts of the surface, both of the disc 

 and the arms, of active uninjured specimens were irritated, both 

 mechanically and chemically, in order to determine the normal dis- 

 tribution of sensation. All parts of the surface were found to be 

 sensitive, but in very unequal degrees. Irritation of the dorsal surface 

 of the calyx caused only slight movements of the arms, unless the 

 irritation were severe or prolonged. Irritation of the dorsal or lateral 

 surfaces of the arms, where the layer of integument is very thin, 

 caused flexion of the arms, with extension of the pinnules close to the 

 irritated spot. The response was usually ready, but the movement 

 only slight. Prolonged or more violent irritation caused exaggeration 

 of the movement, together with approximation of the adjacent arms 

 towards the irritated arm, as though to remove the source of irritation, 

 and in some cases active movement of the whole animal in a direction 

 away from the irritated arm. Irritation of a pinnule causes, according 

 to the degree and duration of the stimulation, movement of the pinnule, 



