106 G. H. PARKER 



with the point to be stimulated first thoroughly narcotized by 

 dropping upon it crystals of magnesium sulphate, the stimulus 

 is followed by a pronounced ring-like constriction in the circu- 

 lar fibers but by hardly any contraction in the longitudinal mus- 

 cles. For these reasons I regard the ectodermic musculature as 

 under the control of nervous elements and the entodermic at 

 least open to direct stimulation. 



Another general feature of the tentacles is the polarity ex- 

 hibited by these organs. Thus the tentacular cilia regularly 

 beat from the base toward the tip of this organ and hence ex- 

 hibit polarization, but this feature is better seen in the neuro- 

 muscular reaction of these parts. When the tip of a tentacle 

 is vigorously stimulated the whole tentacle is likely to respond, 

 but when a point lower down on the side of the tentacle is stimu- 

 lated, the reaction is chiefly from this point proximally. In 

 other words transmission is more readily accomplished from the 

 tip toward the base of the tentacle than in the reverse direc- 

 tion. The same kind of evidence conies from the reparative 

 steps in regeneration. If a tentacle is cut off, the stump con- 

 tracts vigorously and on reexpanding forms a terminal nipple; 

 the cut face of the distal segment usually contracts only a 

 little and seldom if ever closes the open wound. Yet, if such a 

 distal piece is again cut crosswise, its proximal part contracts 

 and eventually forms a nipple while the distal piece remains 

 almost unaffected. The polarization thus exhibited is in the 

 same direction as that which was shown by the reactions of 

 the attached tentacle to mechanical stimulation. 



If the tentacles of an animal which has been thoroughly anes- 

 thetized with chloretone are touched, no response whatever 

 follows. If they are cut neither the proximal nor the distal 

 parts contract but both remain flabbily open. In consequence 

 of these conditions I believe that the polarity of the tentacle in 

 so far as it is exhibited by the reaction just noted is of a nerv- 

 ous nature, for it disappears on applying a drug which elimi- 

 nates nervous activity. 



When the nervous structure in the tentacle of actinians is 

 examined with the view of seeking some condition upon which 



