488 



C. M. Child 



is formed anew from the central portion of the new terminal re- 

 gion (Fig. 17). The new tentacles arise from that region of the 

 body-wall which was originally just aboral to the wound, not 

 from the cut surface itself (Figs. 16 and 17). The diameter 

 of the disc is at first considerably less than the diameter of the 

 column, but as growth proceeds it increases (Figs. 17 and 18). 

 Except in certain special cases to be considered later the number 

 of tentacles is always twenty-four, i.e., the same as the number 

 of mesenteries, and in restitution as in ontogeny, the tentacles 

 arise over those regions which in the new position of the body-wall 

 following inrolling become the oral ends of the intermesenterial 

 chambers. Since Harenactis possesses a definite number of mes- 

 enteries, twenty-four, which extend the whole length of the body, 



new mesenteries are not formed in restitution, though extensive 

 rediff^erentiation of the old mesenteries may occur, e.g., in the case 

 of restitution of an oral end in the suboesophageal region, where 

 the formation of an oesophageal region is involved. 



In Cerianthus the new tissue, or at least the regions where 

 growth is most rapid, differ in color from others, but in Haren- 

 actis new tissue or regions of rapid growth very soon become indis- 

 tinguishable from the other parts. In the case of oral restitution 

 it is quite impossible to determine how far the formation of new 

 material is localized in the oral region after the formation of disc 

 and tentacles. 



In the healing of wounds and restitution where the formation 

 of new tentacles and disc does not occur, i.e., in lateral wounds 

 not involving the oesophagus and in aboral restitution, the new 

 tissue formed is at first distinguishable from the old by greater 



