574 Charles Zeleny 
between the smaller and medium sized isnot very pronounced and 
may not be significant. 
3 In Amblystoma jeffersonianum, larve 131 to 135 days old 
as compared with those 28 to 48 days old regenerate the new tail 
less rapidly both when the whole and when half the tail is removed. 
This is true of the actual rate of increase in length as well as the 
rate per unit of total body length. 
4 In individuals of Portunus sayi ranging from 3.9 to 14.5 
mm. with increase in size of the animals there is an increase not 
only in the rate of proliferation but also in the specific rate. 
The increase in specific rate corresponds with an increase in 
specific size of the chelz in uninjured individuals in such a way 
that in all crabs of the sizes studied new chele are completed in 
the same period of time. 
5 Adult individuals of Cambarus propinquus regenerate less 
rapidly than young ones of the fourth to the sixth molt in actual 
rate of prolification as well as in time necessary to complete the 
removed organ. Among adult individuals ranging in length from 
10.6 to 19.0 mm. the larger (older?) ones have a greater rate of 
regeneration but the time necessary to complete the removed part 
is on the whole greater in the older than in the younger ones. 
6 In Cambarus barton: all individuals were reared in the 
laboratory and their actual age was determined.. The rate of 
regeneration is greater in the older individuals than in the younger 
ones but the specific rate is less and therefore the time necessary 
to complete the whole removed part is greater. 
7 In Palzmon tenuicornis with cephalo-thoracic lengths vary- 
ing from 6.8 to 13.1 mm. the same rule holds as for Cambarus 
bartoni. 
8 In Palzmonetes vulgaris with cephalo-thoracic lengths rang- 
ing from 7.2 to 13.6 mm. there is no evident change in rate 
of proliferation of new material with change in size. The spe- 
cific rate either shows no change or a decrease. 
g The general result is clear that in a majority of the cases 
the actual rate of proliferation of new tissue is greater in older 
than in younger individuals, but this is not sufficient to reproduce 
the removed organ as soon in the older as in the younger indi- 
viduals. 
