WOUND CLOSURE AND POLARITY IN METRIDIUM 461 



contraction of the longitudinal fibers being accompanied by the 

 relaxation of the circular ones. Emphasis should be given to the 

 fact that the three features of the reaction to touch, namely, the 

 local zone of shortening, the bending at the point of stimulus, and 

 the general longitudinal contraction, all involve only that part of 

 the tentacle lying proximal to the point of stimulation. 

 . Parker ('96) observed that in Metridium the cilia of the ecto- 

 derm of the tentacle make a current in the water toward the ten- 

 tacle tip, and that, by means of the cilia, excised tentacles move for 

 a long time with their basal ends directed forward. Tentacle 

 fragments were kept alive in my experiments sometimes for eight 

 days, and in one of Mr. Berry's experiments for a longer period. 

 The ciha moved them during this time in the direction of their 

 basal ends. Dr. Rand found that in Condylactis and Aiptasia also 

 the ciha of the tentacle beat toward the tips of the tentacles. 



One series of our experiments dealt with the behavior of the 

 cut ends of the excised part of the tentacle. When the expanded 

 tentacle was severed, if carefully done, the part cut off contracted 

 in length but slightly, as compared with the stump, but an excised 

 part never regained its full expansion after it contracted. After 

 excision the tentacle was cut into two or more pieces. The level 

 of the cuts varied in different experiments. The following results 

 are from an experiment in which, after the tentacle was severed 

 from the animal, two cuts were made, dividing the excised tenta- 

 cle into three fragments (fig. 4, a, b, c) The tip (c) was first cut off. 

 It scarcely contracted, while the proximal fragment contracted 

 greatly. When, after a few minutes, the proximal fragment had 

 expanded, the cut between h and a was made. The distal frag- 

 ment resulting from this operation scarcely contracted, but the 

 proximal part contracted strongly. Under low magnification all 

 fragments showed transverse wrinkles; these are not shown in 

 the figures. 



The activity of the distal ends of a and b (fig. 4) should be com- 

 pared with that of the distal end of the attached stump from which 

 the tentacle had been cut (as in fig. 1). At the distal cut end of a 

 fragment the abrupt initial inrolling of the edge was followed by a 

 process of quite different character. The opening became smaller 



