ZOOLOGY: C. ZELENY 
485 
FIG. 1 
is proximal to that level. In order to insure equality of level the first 
cut was made at A in the figure for a new tissue basis and at B for an 
old tissue basis, the second regeneration level, in each case coming be- 
tween A and B. If rate 
control is a function ^ ^ 
merely of the readiness 
of the cells the second 
regeneration from the 
new tissue level should 
be more rapid than that 
from the old tissue level. 
Three groups of experiments were made on tadpoles of the green 
frog, Rana clamitans. In each it is clear that there is no striking dif- 
ference between the rates from the two kinds of cells. 
In experiment I the average regenerated length in ten individuals 
at the end of six days is 2.16 mm. from old tissue and 2.15 mm. from new 
tissue. The removed lengths are not exactly alike in the two cases 
and it is necessary to make a correction for the difference. It is shown 
elsewhere that within the limits of the present experiment rate of re- 
generation is directly proportional to length removed. The specific 
length regenerated or length per unit of removed length is therefore a 
constant within these limits. It is therefore fairer to use the specific 
than the absolute lengths. The specific lengths regenerated in the 
present experiment at six days are 0.196 for old and 0.204 for new tissue. 
In the same experiment at eight days the average lengths are 3.19 
mm. from old tissue and 3.12 from new and the specific lengths are 
respectively 0.303 and 0.310. 
These values are given in table 1 . 
TABLE 1 
Comparisons of Regenerations from Old and New Tissue in the Tail of the Tad- 
pole OF Rana Clamitans. Series 3628-3675 
TOTAL 
LENGTH 
TAIL 
LENGTH 
REMOVED 
LENGTH 
REGENERATION TIME 
SIX DAYS 
REGENERATION TIME 
EIGHT DAYS 
Regener- 
ated 
length 
Specific 
length 
regenerated 
Regener- 
ated 
length 
Specific 
length 
regenerated 
mm. 
mm. 
mm. 
mm. 
mm. 
Average from old tissue. 
32.9 
21.5 
11.3 
2.16 
0.196 
3.19 
0.303 
Average from new tissue. 
34.0 
22.2 
10.7 
2.15 
0.204 
3.12 
0.310 
0.01 
0.07 
New — ahead 
0.008 
0.007 
Old — times ahead 
4 
3 
3 
New — times ahead 
6 
6^- 
3 
3 
