FORM-REGULATION IN CERIANTHUS, IV. 

 THE ROLE OF WATER-PRESSURE IN REGENERATION. 



C. M. CHILD. 



INTRODUCTORY. 



The regeneration of the marginal tentacles in cylindrical pieces 

 was described in the first paper of this series (Child, '03^). 



The tentacles do not arise from the new tissue closing the end, 

 nor from the cut surface, but from the old body-wall itself, which 

 first becomes thinner and loses its muscular layer in the region 

 where the tentacles are to appear and then gives rise to small 

 buds, corresponding in number and position to the intermesen- 

 terial chambers. 



The fact that the new marginal tentacles arise some distance 

 away from the cut surface by a local transformation of the already 

 differentiated body-wall is of considerable importance. There 

 must be some adequate ground for the localization of this pecu- 

 liar process of transformation in a region of the body-wall which 

 apparently differed in no way from adjacent parts before the cut 

 was made. 



Very early in my study of regeneration in Ccriantlins it became 

 evident that the rapidity of regeneration was more or less closely 

 connected with the degree of distension of the piece. My obser- 

 vations along this line were made chiefly upon C. solitarius. In 

 cases where closure of the ends and consequently distension by 

 water was possible regeneration was much more rapid than in pieces 

 where communication between the enteron and the exterior - 

 other then the mouth and the aboral pore --existed. Observa- 

 tion of this apparent relation between water-pressure and regen- 

 eration led to experiment and it was soon possible to demonstrate 

 that a very close relation between water-pressure in the enteron 

 and regeneration existed. I am aware, of course, that Loeb 

 ('91, '02) regards certain phases of this relation in CcriantJins as 

 osmotic in nature. The results of his experiments and his inter- 

 pretation will be discussed at another time : it need only be 



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