III. REGENERATION OF VERTEBRATE APPENDAGES
141
proximal to the defect or at a greater distance from it. Most regenerates
were normal, but a small percentage (5 to 10%) repeated the original
anomaly, and others were abnormal in other respects. Second, and even
third, amputations of these defective tails brought about the regeneration of equally deficient tails. The distance of the level of amputation
from the defect had surprisingly little effect on the incidence of abnormal
tails, thus leading the authors to conclude that despite the absence of
visible alterations in the structure of the tails at the levels of amputation,
the original defects were more serious in nature than the anatomical
aberrations would lead one to believe. However, in view of the very
large numbers of supposedly defective tails which regenerated normally
vis-a-vis the relatively small number of cases in which the regenerate
reproduced the original defect, the significance of these results and their
interpretation is problematic.
In an endeavour to resolve some of the inconsistencies in this problem,
Newth (1958a) undertook the task of repeating the earlier work of
Woronzowa and Liosner (1947) in the same species of anuran, as well as
in the axolotl. By appropriate experimental interventions in embryos,
larvae were obtained which lacked either the veutral (axolotl) or dorsal
(R. temporaria) tail fins. Tails amputated proximal to the defective
regions produced almost all normal regenerates (despite 5 abnormal
tails out of a total of 200); those transected through the malformed
parts invariably gave rise to aberrant tail regenerates simulating the
original defect. These results were not altered by repeated amputation
and regeneration (Fig. 6).
Instead of interference in ontogeny, the infliction of defects during
regeneration may also cause the development of abnormal limbs.
Breedis (1952) obtained limbs with hypomorphic accessory outgrowths
following treatment with carcinogens. When the entire limb bearing the
supernumerary appendage was amputated a normal extremity was
regenerated. When just the deficient supernumerary was cut off,
similarly malformed regenerates were produced. In other experiments,
by the present author, half limbs were formed as a result of regeneration
from partially irradiated hind legs (c/. Section VI, C). When these
anomalous regenerates were reamputated slightly distal to the original
level of amputation, they consistently regenerated true to form. In
nearly every case the number of digits in the second regenerate equalled
that in the first. The investigations of Skowron and Roguski (1958) are
especially pertinent in this regard. When muscle and connective tissue
from unirradiated limbs or tails are homogenized and injected into
X-rayed limbs, the subsequent regenerates always conform to the source
of injected material, but are invariably abnormal. Repeated amputations
of these regenerates give rise to equally abnormal replacements.
141
proximal to the defect or at a greater distance from it. Most regenerates
were normal, but a small percentage (5 to 10%) repeated the original
anomaly, and others were abnormal in other respects. Second, and even
third, amputations of these defective tails brought about the regeneration of equally deficient tails. The distance of the level of amputation
from the defect had surprisingly little effect on the incidence of abnormal
tails, thus leading the authors to conclude that despite the absence of
visible alterations in the structure of the tails at the levels of amputation,
the original defects were more serious in nature than the anatomical
aberrations would lead one to believe. However, in view of the very
large numbers of supposedly defective tails which regenerated normally
vis-a-vis the relatively small number of cases in which the regenerate
reproduced the original defect, the significance of these results and their
interpretation is problematic.
In an endeavour to resolve some of the inconsistencies in this problem,
Newth (1958a) undertook the task of repeating the earlier work of
Woronzowa and Liosner (1947) in the same species of anuran, as well as
in the axolotl. By appropriate experimental interventions in embryos,
larvae were obtained which lacked either the veutral (axolotl) or dorsal
(R. temporaria) tail fins. Tails amputated proximal to the defective
regions produced almost all normal regenerates (despite 5 abnormal
tails out of a total of 200); those transected through the malformed
parts invariably gave rise to aberrant tail regenerates simulating the
original defect. These results were not altered by repeated amputation
and regeneration (Fig. 6).
Instead of interference in ontogeny, the infliction of defects during
regeneration may also cause the development of abnormal limbs.
Breedis (1952) obtained limbs with hypomorphic accessory outgrowths
following treatment with carcinogens. When the entire limb bearing the
supernumerary appendage was amputated a normal extremity was
regenerated. When just the deficient supernumerary was cut off,
similarly malformed regenerates were produced. In other experiments,
by the present author, half limbs were formed as a result of regeneration
from partially irradiated hind legs (c/. Section VI, C). When these
anomalous regenerates were reamputated slightly distal to the original
level of amputation, they consistently regenerated true to form. In
nearly every case the number of digits in the second regenerate equalled
that in the first. The investigations of Skowron and Roguski (1958) are
especially pertinent in this regard. When muscle and connective tissue
from unirradiated limbs or tails are homogenized and injected into
X-rayed limbs, the subsequent regenerates always conform to the source
of injected material, but are invariably abnormal. Repeated amputations
of these regenerates give rise to equally abnormal replacements.