454 WAYLAND M. CHESTER 



When the cut was carefully made near the tip, not so often 

 did all parts of this series of results occur. If very near the tip, 

 the tentacle alone reacted, scarcely contracting, the tip closing 

 immediately before collapse could occur. If the cut was between 

 the middle and the base of the tentacle, the series of reactions 

 involving the stump, the adjacent tentacles and the disk almost 

 always occurred, as described above, and the tentacle was hidden 

 for a longer period. In either case, however, the closed end re- 

 sembled that of the tentacle cut midway of its length, though it 

 reached its normal expansion very quickly in a cut at the tip, and 

 very slowly in a cut at the basal end. In the latter case five to 

 ten minutes usually elapsed, and it was sometimes hidden for 

 twenty to thirty minutes. 



The phenomena of closure and the resulting form were not 

 greatly different from those found in Condylactis and Aiptasia 

 (Rand, '09, pp. 195-201) . The polyps of the Metridium used had 

 tentacles that, while tapering as in Condylactis, were very much 

 smaller (one-ninth or one-tenth the length) . The basal diameter 

 was also less than that of the cylindrical tentacles of Aiptasia. 

 The resultant nipple was short, with proportions, relative to those 

 of the tentacle, not greatly different from those of the nipple in 

 Condylactis; but it was not as long, relatively, as that of Aiptasia. 

 The thin black endodermic layer of the otherwise light brown 

 tentacle of the Metridium polyps became very conspicuous in the 

 nipple as an axial pliig, while the tentacle wall showed a gradation, 

 as in Condylactis, from the dense opacity of the nipple to the 

 translucent brown of the tentacle. 



Rand ('09, p. 198-201) found that in the southern forms three 

 successive phenomena are involveti in the closing of the wounded 

 tentacle. These are, first, a slight and immediate inrolling of the 

 cut edge; secondly, the formation of a muscular sphincter or 

 nipple; and, thirdly, the gradual replacement of the nipple by a 

 closed rounded end. 



In a number of my experiments the wounded tentacle collapsed 

 and contracted while the adjacent tentacles did not hide it. In 

 these cases, the activities could be watched from the time of 

 wounding. When the cut was first made, the edges rolled slightly 



