FORM REGULATION IN CERIANTHUS. 309 



from time to time in order to permit distension to occur if there 

 were any tendency. The changes during this time in the one 

 piece which was closed and partly filled are of considerable in- 

 terest. At one side of the closed oral end of the piece a few 

 minute outgrowths 0.2-0.5 mm. in length made their appearance. 

 They resembled marginal tentacles and were situated where 

 these organs should appear, but there were only a few of them 

 close together on one side and no others appeared. Fig. 3 

 shows the piece as it appeared January 21. 

 The new tissue closing the end is indicated 

 by the stippling. At one side are six 

 small outgrowths resembling tentacles, 



but no traces of any others can be found 



FIG. 3. 



at any point of the circumference. At the 



conclusion of the experiment the piece was opened and it was 

 found that a few of the longest mesenteries extended into the 

 piece in the radius in which the outgrowths appeared. This 

 region is then without doubt the region of the directive mesen- 

 teries, and the mesenteries present are simply the longest mesen- 

 teries of the body which lie to the right and left of the short 

 directives and extend nearly to the aboral end. The small out- 

 growths correspond in position with the spaces between these 

 mesenteries and there can be little doubt that they represent 

 marginal tentacles. No other mesenteries are present in the 

 piece, none having regenerated. It becomes evident from the 

 history of this piece that the presence of mesenteries is necessary 

 for the regeneration of marginal tentacles. In pieces from 

 regions nearer the oral end mesenteries are regenerated, but in 

 this piece no trace of regenerated mesenteries could be found, 

 and tentacles have begun to regenerate only in the spaces be- 

 tween such of the old mesenteries as extended into the piece. 



The series as a whole affords several results of importance. 

 As in the preceding series, the decreasing rapidity of regeneration 

 with increasing distance from the oral end of the body is clearly 

 shown. The pieces A regenerate more rapidly than B, B more 

 rapidly than C, and finally D, the aboral pieces, are capable of 

 only a slight degree of regeneration or of none at all, the differ- 

 ence between the one piece which regenerated a few tentacles and 



