406 Marion L. Durbin 
tion of the few animals left to represent the series. However, 
it is not probable that this factor entered into the results until 
after the sixth or seventh measurement was made. ‘Table V 
gives the results for this experiment. 
TABLE V 
Data for Experiment IV. Same explanation as for Table I. 
| OCTOBER NOVEMBER 
a ae ee 
Dates of measure- | | | | 
mle Sao somone | 17 20 || 22) 1/34, 4) 27 cay || ive $2) 2% 15 
mm. amounts of | 
regeneration ...... 0.86 | 2.15 |3.66 | 5.20 |5.95 | 6.38 |7.10 7.60 8.20 | 8.40 
Days in period be- | | | | | | 
tween measure- | | | | 
| | 
ments.......... 3 2 | 2 3 2 2 2) aed: 4 4 
mm. gain during | | 
each period.....| 0.86 | 1.29 | 1.51 | 1.54 | 0.75 | 0.43 0.62 | 0.50 | 0.60 | 0.20 
mm. per day during | 
each period ..... 0.290 0.645 | 0.755 0.510 | 0.370 0.215 0.206 0.125) 0.150) 0.050 
Measurements of | | | | 
control series in| | | | 
POR) Sees aah 7.10 | | 46.04 | | | | 45-10, 44.50 
The structure of the regenerating tail was studied in each 
of the stages represented by the three tadpoles that were killed 
every time a measurement was made. As the earliest stage at 
which material was killed came three days after the operation 
very little can be said with certainty concerning the origin of the 
cells in the regenerated tail. Barfurth® has carefully described 
the beginning of regeneration in the tail of amphibian larve and 
his description of the process agrees very well with what can be 
made out from the present preparations. The points bearing 
on this study are: (1) The cells of the ectoderm are proliferated 
from the innermost layer of the old ectoderm. (2) The cells 
from which the core of the new notochord arises come from 
cells that form a layer just inside of the wall of the old noto- 
6 Barfurth, D.: Die Erscheinungen der Regeneration bei Wirbeltierembryonen. Handbuch der Ente 
wickelungslehre der Wirbeltiere. Herausgegeben von O. Hertwig. Jena. 1903. 
