WOUND CLOSURE AND POLARITY IN METRIDIUM 459 



POLARITY 



The results of tactile stimulation showed in the Metridium the 

 very significant physiological polarity that was found by Rand 

 ('09, p. 223) in the southern actinians. This polarity consists in 

 differences in the reactions on the proximal and distal sides of the 

 point of stimulation. My results, however, differ from those of 

 Dr. Rand in the details of the reactions. When a tentacle is 

 gently touched with a glass' rod or needle point, there is a slight 

 thickening of a narrow zone proximal to the point of contact. 

 This is evident by the barely perceptible enlargement of the girth 

 of the .zone and by the lighter color as the wall becomes opaque. 

 In sluggish animals, viewed under a low power lens, the contrac- 

 tion is evident, not only by the change of color, but by wrinkling 

 of the contracted band. This band is undoubtedly due to a con- 

 traction of longitudinal muscle fibers, but the contraction takes 

 place only on the proximal side of the point of contact. In a 

 more vigorous animal, or with a stronger stimulation of the ten- 

 tacle of a sluggish one, the touch of the needle point produces an 

 evident bending of the tentacle at the place touched and toward 

 the point of contact; and this may be immediately followed by the 

 swaying of the tentacle. The swaying, however, is produced by 

 contractions that are entirely proximal to the point of contact, 

 and the distal part of the tentacle is thereby bent stiffly first one 

 way and then another. The bending of the tentacle toward the 

 point of contact is not always followed by the swaying of the ten- 

 tacle. This latter part of the reaction to touch is similar to the 

 reaction to the approximation of food, in which the tentacle moves 

 to and fro. It differs in the localization of the muscular contrac- 

 tion. In the touch reaction, the contraction is entirely proximal 

 to the point of contact ; in the feeding reaction, there may be con- 

 traction in the whole length of the tentacle. In the reaction to 

 touch, the distal part is moved by the bending of the proximal; 

 in the feeding reaction the whole tentacle waves. If the tentacle 

 is touched when the distal part is curved or bent, this part may 

 appear to wave. But it is simply carried through the water by 

 the movement of the proximal part of the tentacle. A general 



