FORM REGULATION IN CERIANTHUS. 259 



Fig. 3 1 shows a still later stage in which the new tissue is 

 becoming pigmented. The appearance of the pigment corres- 

 ponds in time with the differentiation of the muscular layer, and 

 I am inclined to believe that in CcriantJins as in various other 

 forms, the pigmentation of the body is closely connected with 

 the presence and arrangement of the muscular layer. 



The course of regeneration described in the present paper is 

 characteristic of pieces cut from the middle half of the body. In 

 following papers the regeneration of pieces from various regions 

 will be compared, and experiments determining some of the fac- 

 tors concerned in regeneration will be described. 



SUMMARY. 



1. In cylindrical pieces of Ccriautliits obtained by two trans- 

 verse cuts collapse occurs at once and the cut ends begin to roll 

 inward soon after section, finally coming into contact and closing 

 the opening more or less completely. Since little or no transverse 

 contraction of the infolded margins occurs they are thrown into 

 numerous radiating folds and wrinkles. 



2. Within two to three days after section a thin membrane 

 formed by the growth of new tissue from the cut surfaces closes 

 the two ends completely. The piece now becomes gradually 

 distended with water, probably owing to the accumulation of 

 metabolic products in the enteron and consequent diffusion of 

 water into this closed cavity. As distension proceeds the in- 

 folded margins of the body-wall at the two ends are forced apart 

 by internal pressure and the area occupied by the thin membrane 

 increases. 



3. The first step in the regeneration of tentacles is the forma- 

 tion of a slight ridge, the marginal tentacular ridge, on the oral 

 end. This ridge is formed wholly within the tissue of the old 

 body-wall, its formation being accompanied by reduction and 

 disappearance of the muscular layer, disappearance of the pig- 

 ment and great reduction in thickness. The marginal ten- 

 tacles first appear as slight upgrowths from the highest most 

 oral point of the ridge, one tentacle corresponding to each in- 

 termesenterial chamber. The position of the mesenteries is indi- 

 cated externally on the tentacular ridge by slight furrows which 

 separate the regenerating tentacles from each other. 



