THE DYNAMIC FACTOR IN REGENERATION. 269 



ing up of hydranth formation as such, but the initial inhibition is 

 overcome. 



The special problem with which this paper deals is the nature 

 of what takes place at the basal ends when the oral end is kept 

 open and when it is tied. Is the retardation of such a kind that 

 a slower process of development is going tin at the basal end 

 while the oral end is developing, or does the basal end not really 

 begin to develop until the oral end has formed its polyps. If so, 

 what gives it its start later ? The following experiments were 

 devised to study these questions. 



Experiment I. - - The purpose of the experiment was to deter- 

 mine whether when both oral and basal ends of a piece are left 

 open constructive changes are slowly going on at the basal end. 

 Some pieces were cut off and left open (A) ; later other pieces 

 were cut off and the oral ends tied (Z>') and at the same time the 

 oral ends of (A) were tied. It was found that the basal ends of 

 the (A) pieces did not develop faster than those of the (>) pieces, 

 showing that the changes at the basal end of (A) are not pro- 

 gressing, but are held in check by the developing oral hydranth. 



Control I. - - In some pieces the old hydranths were left intact 

 and the pieces cut off. No basal hydranths began to develop 

 until the old heads began to be absorbed. The presence of the 

 old heads inhibited the development of the basal hydranths until 

 the heads had degenerated when the latter appeared. 



Experiment II. In order to find out whether, when the oral 

 end is tied, changes take place throughout the piece that tend to 

 make more rapid the development of basal hydranths, or whether 

 these changes are localized at the basal end where the new hy- 

 dranth develops, the following experiment was tried. The oral 

 ends of many pieces of the same length were tied. Then after 

 several hours' interval differing in several experiments, the basal 

 end was cut off, (a] just inside of the area that would form the 

 basal hydranth, (&) in the middle of the piece, (c) just below the 

 ligature. In general the development of the basal hydranth was 

 delayed as compared with control pieces tied but not cut off 

 at the basal end ; the delay was the greater the further re- 

 moved the cut from the basal end, despite the fact that oral levels 

 tend to regenerate faster than more basal levels. The differences 



