Effect of Age upon Regeneration 569 
of chela in 13.8 days in two molts. The specific amount is 0.27 
mm. and the specific rate 0.0195. 
Adult crayfish on the other hand take a much longer period 
to complete a single molt and the propodite of the regenerated 
chela is on the average 6.47 mm. long in males and 6.14 mm. 
in females. This gives a specific amount of regeneration of 0.444 
and a specific rate of 0.0049 for the males and a specific amount 
of 0.400 and a specific rate of 0.0030 for the females. Likewise 
in case both chela are removed the length of the regenerated 
chelz is 6.4 for males and 6.07 for females and the corresponding 
specific amounts and specific rates are 0.435 and 0.0080 for the 
males and 0.404 and 0.0078 for the females. 
The specific rates are therefore decidedly greater in the young 
crayfish than in the adults. The young however have had two 
molts as opposed to one in the adults. 
The second comparison concerns the adults alone. If the 
smaller (younger ?) adults are compared with the larger (older °) 
ones the actual regeneration lengths are greater in the larger 
than in the smaller ones. The specific amounts are practically 
alike in both groups. ‘The specific rates however are slightly 
greater in the younger than in the older individuals, so that the 
former should complete their chelz slightly sooner than the latter. 
The data on Cambarus propinquus are unsatisfactory as regards 
the comparison between very young animals and adults because 
the regeneration periods under observation are so different. ‘This 
criticism does not apply to the comparison between small and 
large adults. 
When very young individuals are compared with adults there 
is evidently a greater rate of regeneration in the younger than in 
the older individuals not only in the sense of the time necessary 
to complete a new organ but also in the sense of rate of prolifera- 
tion of new material. When younger and older adults are com- 
pared however, it is seen that the actual rate of proliferation is 
greater in the older individuals but the time necessary to com- 
plete the missing chela is nevertheless greater. 
