51] RATE OF REGENERATION— ZELENY 51 



viduals on April 5. The new tissue was removed on April 17 and 

 again on May 1, May 10 and May 19, making five removals in all. 

 The second removal gives the first regeneration, the third the second, 

 and so on. The regenerated lengths were therefore determined by 

 measurement of removed parts. This does not give as accurate a deter- 

 mination as does direct measurement without removal because the cut 

 can not in ordinary practice be made exactly at the border line between 

 old and new tissue. 



The data are given in Table 34. The first regeneration covers a 

 twelve-day period, the second fourteen days and the third and fourth 

 each nine days. 



The third and fourth regenerations are the only ones that have the 

 same time interval. Ten individuals are available for this comparison. 

 The average for the third regeneration for these ten is 1.30 mm. and 

 of the fourth regeneration 1.17 mm. When all individuals are taken 

 without regard to representation of both regenerations the average for 

 the third regeneration is 1.28 and for the fourth 1.17. In seven of the 

 ten former cases the third is ahead of the fourth regeneration, in two 

 they are tied and in one the fourth is ahead of the third. The data 

 therefore show an advantage of the third over the fourth regeneration. 



The first regeneration ran twelve days and the second fourteen 

 days. The maximum rate of regeneration comes on or near the ninth 

 day and the rate has declined to a low point by the fourteenth day. 

 However it is not possible to make the necessary correction because of 

 lack of data on the rate curve for this particular set of larvae. Some 

 facts may however be obtained by a comparison. Sixteen individuals 

 for each of the two regenerations are available for comparison. The 

 average for the first regeneration in these is 2.06 mm. and for the sec- 

 ond 2.01 mm. In seven the first is ahead of the second, in seven the 

 second is ahead of the first, and two are tied. When all individuals 

 are taken without regard to representation of both regenerations the 

 average for the first regeneration is 1.99 ± 0.03 mm. for a twelve-day 

 period and for the second regeneration 2.01 for a fourteen-day period. 

 The difference between the two values is not significant, but when the 

 longer time interval taken by the second regeneration is considered the 

 conclusion is reached that the first regeneration is more rapid than the 

 second. 



The data thus indicate a progressive decrease in rate from the 

 first to the fourth regenerations. This result taken in connection with 

 the results obtained from the experiments in which the age factor is 

 eliminated makes it highly probable that the decrease in rate of regen- 

 eration observed here is due to increase in age and not to the effect of 

 successive removal. 



