FORM REGULATION IN CERIANTHUS. 6/ 



a thin membrane of new tissue between those regions of the cut 

 surface which are sufficiently approximated ; the growth of this 

 membrane until the whole opening is closed ; the increase in 

 size of the area of new tissue as the piece becomes distended. 



During the course of my experiments it was found that certain 

 definite conditions are necessary for this growth of new tissue. 



Mention was made of the fact that the new tissue appears first 

 in the folds and wrinkles where two cut surfaces are most closely 

 in contact and that from these regions it extends until closure is 

 complete. In pieces rolled spirally (Figs. 17, 19, 24) or in any 

 such manner that the cut surfaces are not brought into contact 

 no appreciable growth of new tissue occurs ; the cut edges heal, 

 but may remain without further change for months. 



Thus, in these spirally or transversely rolled pieces typical 

 regeneration of new tissue from the cut surface does not occur. 

 Moreover, this is true of all cases in which there is no approxi- 

 mation or contact of two cut surfaces or parts of a cut surface. 

 Never is a thin membrane of new tissue found growing out from 

 a cut surface and without other connections. When present it 

 always connects two cut surfaces or the two sides of a fold where 

 different regions of the cut surface have been approximated. 



This is a point of considerable importance ; indicating as it does 

 that there is nothing in the cut surface itself which initiates re- 

 generation, the necessary condition being found rather in the 

 relations of different cut surfaces or their parts. Never do we 

 find regeneration of the body-wall occurring in the manner 

 represented in the diagram, Fig. 25, as a continuation with free 

 margin of the old tissue. New tissue arising from cut surfaces 

 always appears between two cut surfaces which are in contact or 

 closely approximated as in Fig. 2. These surfaces become 

 united by new tissue which then increases in amount under cer- 

 tain conditions, thus forming a thin membrane connecting the two 

 parts of the cut surface. In the ordinary closure of the end of a 

 cylindrical piece the new tissue first appears, as has been noted, 

 in the folds and wrinkles where parts of the cut surface are 

 closely approximated (Figs. 68, '03^), but from this it spreads 

 rapidly until the whole space is covered and the end closed 

 (Fig. 9, '03). 



