486 
ZOOLOGY: C. ZELENY 
In experiment II similar data were obtained for four, six, eight, ten, 
twelve and a half, eighteen and fifty-six days of regeneration. The 
removed lengths are quite different in the different individuals so that 
specific lengths alone are valid. Giving the old tissue level first in 
each case and using only removals of over 4 mm. these values for the 
seven times are respectively 0.043 and 0.045, 0.135 and 0.143, 0.216 and 
0.224, 0.292 and 0.293, 0.331 and 0.337, 0.352 and 0.348, and 0.345 and 
0.346. They are given in more detail in table 2. 
TABLE 2 
Comparison of Regenerations from Old and New Tissue in the Tail of the Tad- 
pole OF Rana Clamitans, Series 3676-3765 
DAYS OF 
REGENERATION 
OLD TISSUE 
SPECIFIC LENGTH OF 
REGENERATION 
NEW TISSLT- 
SPECIFIC LENGTH OF 
REGENERATION 
OLD AHEAD 
NEW AHEAD 
4 
0.043 
0.045 
0.002 
6 
0.135 
0.143 
0.008 
8 
0.216 
0.224 
0 008 
10 
0.292 
0.293 
0.001 
m 
0.331 
0.337 
0.006 
18 
0.352 
0.348 
0.004 
56 
0.345 
0.346 
0.001 
0.003 
Similar results were obtained when the removed lengths were under 
4 mm. 
In experiment III completed lengths from old and new tissue are 
compared in each of the third, fourth and fifth regenerations. It is 
necessary to point out that in the tadpole tail the completed regenera- 
tion is always less in length than the removed tail. The comparison 
here therefore concerns the degree of replacement of the lost part 
and not its rate. The average regenerated lengths giving the old 
tissue levels first are 7.9 mm. and 7.9 mm. for the third, 5.3 and 5.5 for 
the fourth and 6.6 and 5.9 for the fifth successive regeneration. 
The data as a whole show clearly that there is no essential differ- 
ence between rate of regeneration from new cells and from old cells. 
There is only a very slight advantage in favor of the new cells while a 
striking one would be expected if rate were largely determined by local 
cell characteristics. Rate of regeneration seems therefore to be under 
central control. This conclusion is in agreement with the results of 
experiments on other factors. 
The full data will be published in the University of Illinois Biological 
Monographs. 
