Factors of Form Regidatioyj in Harenactis Attenuata 505 



the wound and renders possible its closure by new tissue, but under 

 other conditions closure becomes physically impossible, although 

 contraction occurred in the usual manner. 



2 Growth of new tissue occurs only under a certain degree of 

 mechanical tension, therefore, no appreciable degree of growth 

 occurs on a single free cut surface. Closure of wounds by new 

 tissue occurs only when two cut surfaces, or two parts of a cut 

 surface are closely approximated to each other or partly in con- 

 tact. The conditions determining the extension over the opening 

 of the thin membrane of new tissue are such as to indicate that 

 the physical factor of capillarity plays an important role in the 

 process. 



3 Union may occur between any two cut surfaces which hap- 

 pen to come into contact, without any relation to the "normal" 

 form. Under the usual conditions the gross anatomical feature 

 of the region concerned in a particular case, e.g., the oesophagus, 

 the mesenteries, the retractor muscles, etc., determine whether 

 and how closure shall occur under certain conditions, e.g., in 

 pieces from the oesophageal region, these anatomical factors deter- 

 mine that closure shall occur in such a manner that continued 

 existence becomes 'mpossible. 



4 As in Cerianthus, the tentacles are not outgrowths from a 

 wound, but localized differentiations in a continuous sheet of 

 tissue. 



5 The rapidity of wound closure and of oral restitution de- 

 creases with increasing distance of the level from the original oral 

 end. This decrease is not uniform, being small in amount in the 

 oral two-thirds of the body and much greater in the aboral third. 

 In small pieces from the extreme aboral end oral restitution does 

 not occur, but closure of the wound may take place sooner or 

 later, the reaction being slow. 



6 In cases where oral restitution does occur in small pieces 

 from the proximal region of the body the number of tentacles is 

 sometimes twelve instead of twenty-four. This development of 

 only half the usual number of tentacles is probably a result of dis- 

 appearance of the secondary cycle of mesenteries in these very 

 small pieces, i.e., a phenomenon of size rather than of region, 



