530 A. MILNES MARSHALL. 



movements of the arms, unless the irritation were severe oi* 

 prolonged. Irritation of the dorsal or lateral surfaces of the 

 arras^ 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 exaggera- 

 tion 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, movement 

 of the whole arm, approximation of the adjacent arms to the 

 aff'ected one, or active movement of the whole animal away from 

 the source of irritation. Irritation of the oral pinnules causes, 

 as already noticed, immediate and very active flexion of all the 

 arms, so as to close in over the disc. 



The epithelium of the ambulacral grooves is extremely sensi- 

 tive, and the results of stimulation are very definite. The 

 slightest irritation causes instantaneous movement of the four 

 or five pairs of pinnules immediately adjacent to the irritated 

 spot, the pinnules being folded alongside the ambulacral groove 

 so as to close it in and grasp the needle or other source of 

 irritation. If the stimulation be continued the arm is actively 

 flexed and the adjacent arms applied to it, and rubbed along 

 the affected part, as though to remove the source of irritation. 

 Finally, irritation of the ventral surface of the disc between the 

 ambulacral grooves causes movements of the arms, but not 

 nearly so active as when the oral pinnules are touched. 



Experiment 11. — An active specimen was eviscerated, and 

 left for half an hour. The calyx, arms, and pinnules were 

 then successively stimulated, as in the preceding experiment. 

 The results were exactly the same, showing that the communi- 

 cation betwen the sensitive surface of any part of the calyx, 

 arms, or pinnules, and the motor mechanism of all the arms, is 

 placed elsewhere than in the visceral mass. 



