Effect of Age upon Regeneration 567 
In older individuals the length of the regenerated tails is less; 
for age 131 days, length 51.6 mm. and regeneration period of 
14 days it is 4.22 mm. or 0.30 mm. per day; for age 134 days, 
length 54.1 mm. and regeneration period of 11 days it is 2.96 
mm. or 0.27 mm. per day; and for age 135 days, length 51.6 
mm. and regeneration period of 10 days it is 3.4 mm. or 0.34 
mm. per day. 
A similar result is obtained when only one-half of the tail is 
removed. For age 28 days, length 22.6 mm. and regeneration 
period of 24 days in the one individual available the length of 
the regenerated tail is 7.7 mm. or 0.32 mm. per day; for age 34 
days, length 27.3 mm. and regeneration period of 15 days in 
the six individuals available the average length of the regen- 
erated tail is 3.8 mm. or 0.25 per day; and for age 48 days, length 
26.7 mm. and regeneration period of 15 days it is 3.8 mm. or 
0.25 mm. per day in the fourteen available individuals. 
For the older individuals there is a decrease in the actual length 
and rate of regeneration as compared with the younger ones. 
For age 131 days, length 49.1 mm. and regeneration period of 
14 days the average length of the regenerated tail in the four 
available individuals is 3.0 mm. or 0.21 mm. per day; for age 
134 days, length 52.4 mm. and regeneration period of 11 days 
it is 2.3 (—) mm. or 0.21 (—) mm. per day; and for age 135 
days, length 51.9 mm. and regeneration period of 10 days it 1s 
1.75 (—) mm. or 0.17 (—) mm. per day. 
The data as a whole show that in the salamanders 131 to 135 
days old the rate of proliferation of new material in length 1s 
less than it is in salamanders 28 to 48 days old. ‘The specific 
rate is obviously still more strikingly less than the actual rate of 
proliferation. 
