35] RATE OF REGENERATION— ZELENY 35 



Beginning with the tenth day the first is ahead. In general the advan- 

 tage of the first increases as time goes on. The growth of new tissue 

 does not terminate until the eighteenth day or after. 



At the % level there are five individuals for the first and ten for 

 the second regeneration (Table 26). The second is ahead of the first 

 until the tenth day, after which the first is in the lead. Regeneration 

 is not stopped until the eighteenth day or later. 



At all four of these levels the specific length of the second regen- 

 eration tends to be ahead until the tenth day (Table 28 and Figure 2). 

 The maximum rate of regeneration is reached before this time and some- 

 what earlier by the second than by the first regeneration, hence the 

 relative gain by the latter after the tenth day (Table 30 and Figure 3). 

 The stopping of regeneration also comes earlier for the second than for 

 the first regeneration as does the beginning of absorption of regenerated 

 material. 



The data in Experiment I concern the amount of regeneration at 

 six and at eight days. At the corresponding times in Experiment II 

 the second regeneration is ahead of the first. There is a full agreement 

 between the two experiments in this regard. 



The more rapid rate of the second regeneration at the start may 

 at first sight seem to be due to the presence of at least 

 some cells which have been actively engaged in previous regenerations. 

 If the second cut comes outside of the boundary between old and new 

 cells the latter cover the whole new cut surface. Even if the cut seems 

 to be exactly at the original cut level there will be some new cells at 

 the regenerating surface. These cells which are already regenerating 

 may be expected to adjust themselves more readily to the new conditions 

 than old ones which have not been engaged in such a process. In another 

 place the relative rates from old and from new tissue are described 

 and a slight early difference favoring the new tissue is made out. While 

 this slight initial advantage may be explained in this way it is probably 

 confined to the period of cell migration and is not a factor in the period 

 of cell division which begins on the second day or later. It is evident 

 that on the whole the control of rate is not a matter inherent in the 

 cells in the neighborhood of the cut surface. Indications point rather 

 to a more central control of the process. 



