THE DYNAMIC FACTOR IN REGENERATION. 27! 



basal ends. I was particularly anxious to settle this point defi- 

 nitely, for obviously, if such acceleration could be proved, it 

 would furnish evidence in favor of a chemical process, especially 

 since other experiments had seemed to show that the basal end 

 does not begin its development when both ends are left open. I 

 have carried out rather an extensive series of experiments that 

 give, I think, a definite answer to the question. 



When pieces are left open at both ends from four to nine hours, 

 and are then tied at the oral end, the basal development is slightly 

 retarded as compared with its development in pieces tied at once. 

 There is little evidence in favor of the view that the later tied 

 pieces can make good the loss of four to nine hours, and of 

 course they can not catch up if a longer time elapses. Whether 

 they may do so in later stages is more difficult to decide, but 

 this does not concern the main point here raised. 



Individual differences in rate, differences in stems, and uncon- 

 trollable differences in level tend to obscure results that depend 

 on only four, six, and nine hours differences in start. The above 

 statement holds, therefore, only for average results. There was 

 found no evidence in favor of actual acceleration, whether there is 

 some relative acceleration is difficult to decide. If the hydranths 

 do not develop promptly /. c., if a long time elapses between the 

 tying and the appearance of hydranths, the initial differences of 

 a few hours may be lost. 



Experiment VI. Another attempt was made to see whether 

 changes take place in the piece as a whole, after it is cut off, that 

 make more rapid the development of an oral hydranth when a 

 new cut is made. 



Pieces were removed and after four hours somewhat more than 

 the oral hydranth region was cut off. In some cases the newly 

 cut ends developed as fast as did the hydranth in the small pieces 

 cut off, but the latter may have been retarded by the operation or 

 by the smallness of the pieces ; yet in some cases the development 

 of the newly cut ends was as rapid as in control uncut pieces. 

 This result indicates that changes take place in the pieces behind 

 the actual region of hydranth formation that lead toward the 

 development of a hydranth. 



Experiment VII. In this case pieces first cut off were after 



