FORM-REGULATION IN CERIANTHUS. 269 



From this time on the three experimental pieces were left 

 undisturbed in order to determine whether, after closure of their 

 aboral ends and distension, the tentacles would regain their 

 original length. 



December 28. 37 days after section. Experimental pieces. 

 All healed aborally and fully distended with water. During the 

 eleven days since December 17 the tentacles gradually elon- 

 gated. In the three pieces the lengths of the tentacles were as 

 follows: marginal tentacles, 12-15 mm., 11-12 mm., 10 mm. ; 

 labial tentacles, 5 mm., 4 mm., 3-4 mm. 



The longest tentacles at this time belong to the piece which 

 originally possessed the longest tentacles, viz., marginal, 20 mm., 

 labial, 7 mm. 



Controls.- -In no case do the tentacles show any appreciable 

 reduction in length. 



No further increase in length of the tentacles of the experi- 

 mental pieces occurred. 



During the first 26 days the marginal tentacles of the ex- 

 perimental pieces decreased more than 50 per cent. They were 

 more or less completely collapsed during this period, and as a 

 collapsed tentacle is always shorter than one that is distended, it 

 may appear at first glance that the reduction in length repre- 

 sents merely this difference. This, however, is not the case. 

 During the first few days following section the collapsed ten- 

 tacles were only slightly shorter than they had been when dis- 

 tended and a continuous gradual reduction in length took place 

 up to December 17. During the following period of eleven 

 days in which closure and renewed distension occurred, the ten- 

 tacles elongated gradually. If the reduction in length had repre- 

 sented only the difference between a collapsed and a distended 

 tentacle it might be expected that the tentacles would regain 

 their original length immediately or almost immediately after the 

 internal pressure and distension were again established. But the 

 increase in length was gradual, although the tentacles were ap- 

 parently fully distended about December 21. Moreover, they 

 never regained their original length, the maximum being 70 per 

 cent, of the original length. 



These facts render it evident that an actual reduction in the 



