566 Charles Zeleny 
than that of age and they therefore unfortunately are subject to 
the error of difference in length of the regeneration period. 
The rate of regeneration in length following an operation is at 
first slow, then increases rapidly to a maximum, after which it 
declines slowly to zero, which it reaches at the completion of 
regeneration. ‘Table 6 is especially subject to this error because 
it covers a much longer period than the others. ‘This factor 
however in no way invalidates the general conclusion to be drawn 
from the data. 
The specific rate of regeneration. \he average specific rate of 
regeneration of the tail in length is 0.0439 for individuals with a 
total body length of 22.6 mm., age of 28 days at the time of the 
operation and a regeneration period of 24 days; 0.0396 for those 
26.5 mm. long, 34 days old and with a regeneration period of 15 
days; and 0.0368 for those 26.8 mm. long, 48 days old and with | 
a regeneration period of 15 days. 
This is considerably greater than the specific rate for the older 
salamanders. For those 51.6 mm. long, 131 days old and with 
a regeneration period of 14 days the specific rate is 0.0148; for 
those 54.1 mm. long, 134 days old and with a regeneration period 
of 11 days it is 0.0126; and for those 51.6 mm. long, 135 days old 
and with a regeneration period of 10 days it is 0.0167. 
The above applies to the cases in which nearly the whole tail 
was removed. A similar result is obtained when one-half of the 
tail is removed. ‘The respective specific rates are then 0.048 
0.042 and 0.038 for the younger and 0.020, 0.018 (—), and 0.014 
(—) for the older animals. 
Actual length of regenerated material. Not only is the specific 
rate less in the older than in the younger individuals but also 
the actual length of regenerated material 1s less. 
The individuals with the whole tail removed are considered 
first. For age 28 days, length 22.6 mm. and regeneration period 
24 days, the length of the regenerated tails is 9.36 mm. or 0.39 
mm. per day; for age 34 days, body length 26.5 mm. and regen- 
eration period of 15 days, the length of regenerated tails is 6.22 
mm. or 0.41 mm. per day; and for age 48 days, length 26.8 mm. 
and regeneration period of 15 days the length of regenerated tails 
is 5.87 mm. or 0.39 mm. per day. 
