27] RATE OF REGENERATION— ZELENY 27 



tissue and in individual d it came outside of that line. Of the two indi- 

 viduals available for second regeneration in each set, the one with the 

 cut nearer to the tip of the tail was chosen as individual c and the other 

 as individual d. In this way the second regeneration levels were equal- 

 ized. A first removal of a half of the tail was made in individuals a 

 and b at the same time that the second removal was made in c and d. 

 A direct comparison of the rate of the second regeneration with that 

 of the first was thus made possible without the complication due to 

 internal factors such as difference in age, or external factors such as 

 temperature and food. 



Measurements of regenerated lengths were made at the end of 

 six and of eight days, other experiments having shown that the period 

 of most rapid growth comes at about this time. 



Elsewhere there is a comparison of the rate of regeneration from 

 new tissue with that from old tissue. Here the chief concern is the 

 comparison of the rate of the second regenerations, including both old 

 tissue and new tissue levels, with first regenerations. 



Data The results of the experiment are given in Table 19 for six- 

 day regenerations and in Table 20 for eight-day regenerations. At the 

 end of six days the average length of first regenerations is 2.01 mm. 

 and of second regenerations 2.18 mm. The first exceeds the second in 

 two cases, the second exceeds the first in eight and one is tied. The 

 corresponding average specific amounts are 0.194 and 0.205. In five 

 cases the first exceeds the second and in six the second exceeds the first. 



At eight days the average length of the first regenerations is 3.06 mm. 

 and of the second 3.42 mm. The first exceeds the second in three sets 

 and the second exceeds the first in seven sets. The corresponding aver- 

 age specific amounts are 0.298 and 0.323. In four the first exceeds the 

 second regeneration and in six the second exceeds the first. 



Comparing the first regenerations on the one hand with second 

 regenerations from old tissue and on the other hand with second regen- 

 erations from new tissue it is found, including only complete sets, that 

 at the end of six days the average first regeneration length is 2.01 mm. 

 while that of the second from new tissue is 2.15 mm. and from old tissue 

 2.16 mm. The corresponding average specific amounts are 0.194 for 

 first regenerations and 0.196 for second regenerations from old tissue 

 and 0.204 for second regenerations from new tissue. 



At eight days the first regeneration lengths average 3.06 mm. while 

 second regenerations from old tissue average 3.19 and those from new 

 tissue 3.12. The corresponding specific lengths are 0.298 for first regen- 

 erations and 0.303 for second from old tissue and 0.310 for second from 

 new tissue. 



