FORM-REGULATION IN CERIANTHUS. 137 



September ig. Seven days after section. Examination showed 

 that none had closed, the cut margins rolling in on all sides having 

 rendered closure impossible. Figs. 9 and 10 show two of the 

 pieces as they appeared at this time. In the case of Fig. 9 the 

 longitudinal cut separated both sides of the body at the aboral 

 end and one of the lobes thus formed overlaps the other in the 

 figure. The cut margins at the oral end are inrolled and united 

 by new tissue much as in a cylindrical piece, but aboral to this 

 region the two margins separated by the longitudinal cut have 

 rolled in independently leaving a large open space between them. 

 On the oral end are a few minute tentacle-buds - - far below the 

 normal number. 



In Fig. 10 the inrolling has been somewhat different: on the 

 right side of the figure it is much the same as in Fig. 9 but 

 on the left, instead of rolling longitudinally the oral and aboral 

 parts of the wall have rolled more or less transversely and in 

 opposite directions. At the oral end only a part of the cut 

 surface is exposed, the remainder being rolled inward behind the 

 visible portion in the figure. The exposed portion of the oral 

 end, corresponding to the longitudinally inrolled part of the 

 body-wall is closed by thin new tissue where opposing cut sur- 

 faces are approximated in the inrolling, and bears a few minute 

 tentacle-buds. 



The third piece differs in detail from the other two as regards 

 inrolling, but resembles them in that a few minute tentacle-buds 

 are present and the enteron is widely open to the exterior. 



In the first case (Fig. 9) the transverse section of each inrolled 

 portion would show the form of a spiral with the longitudinal 

 cut surface forming its innermost end : the same is true of the 

 part on the right of Fig. 10, though here the inrolling is less 

 complete. In these portions the contact between different parts 

 of the body-wall is sufficiently close to permit a slight accumu- 

 lation of water in the inner regions of the spiral and therefore a 

 slight distension. The pressure in these parts never approaches 

 that in the normal animal ; as soon as it reaches a certain point 

 escape of the water occurs between the approximated surfaces. 

 Considering the tentacles, we find that their appearance is delayed. 

 Cylindrical pieces closing in the typical manner regenerate tenta- 



