488 
ZOOLOGY: C. ZELENY 
second exceeds the first in six. The corresponding specific lengths or 
lengths regenerated per unit of removed length are 0.194 and 0.205. 
The first regeneration exceeds the second in two sets, the second ex- 
ceeds the first in five and one is tied. The second regeneration has the 
advantage in all the comparisons. 
At eight days the average first regeneration length is 3.06 mm. and 
the second 3.42 mm. The first exceeds the second in three sets and the 
second exceeds the first in seven. The corresponding average specific 
lengths are 0.298 and 0.323. The first regeneration exceeds the second 
in four sets and the second exceeds the first in six. The second regen- 
eration has the advantage in all the comparisons. 
This advantage of the second regeneration over the first in experi- 
ment I holds true of second regenerations from both old and new tissue 
levels. 
FIG. 1. CHANGE IN SPECIFIC RATE OF REGENERATION DURING THE REGENERATION 
PERIOD FOR BOTH FIRST AND SECOND REGENERATIONS. TADPOLE TAIL OF RANA 
CLAMITANS. UNBROKEN LINE = FIRST REGENERATION. BROKEN LINE = SECOND RE- 
GENERATION. 
FIG. 2. SPECIFIC REGENERATED LENGTHS DURING THE REGENERATION PERIOD FOR 
BOTH FIRST AND SECOND REGENERATIONS. TADPOLE TAIL OF RANA CLAMITANS. UN- 
BROKEN LINE = FIRST REGENERATION. BROKEN LINE = SECOND REGENERATION. 
In experiment II, also with Rana clamitans, operations were made 
at the To, i, i and f levels in a sufl&cient number of individuals to yield 
valid data. Regeneration measurements were made at each of these 
levels 4, 6, 8, 10, 12|, 18 and 56 days after the operations. The second 
regeneration at these levels is ahead of the first until about the twelfth 
day after which the first regeneration catches up. The maximum rate 
for both regenerations is reached before this time, and earlier for the 
second than for the first regeneration. The relation between the rates 
is given in figure 1 and between the total regenerated lengths in figure 2. 
In experiment III two-thirds of the tail was removed in larvae of the 
salamander, Amblystoma punctatum. A comparison of the first, 
second and third regenerations was made at 2, 4, 6, 8, 10 and 14 days. 
At two days the first, second and third regenerations average respec- 
