III. REGENERATION OF VERTEBRATE APPENDAGES
117
by Lodyzenskaia (1928) and Abeloos and Lecamp (1931). Whereas limb
blastemas cut off and replaced in their normal orientations developed
into normal regenerates, reimplantation of blastemas after 180° rotation resulted in the production of abnormal regenerates (duplications,
Polydactyly, etc.). Axial conflicts result in abnormalities.
It is logical to interpret these data as indicating that young blastemas
are morphogenetically undetermined and therefore exhibit developmental patterns commensurate with the locations to which they are
transplanted. In contrast, older blastemas are presumably determined
and thus develop as they would had they not been transplanted. In
intermediate cases, both the blastema and the stump may express their
morphogenetic potentialities thus producing abnormal regenerates in
the form of chimerae. Yet it is still not conclusively proved that young,
undetermined blastemas can really develop into alien structures (e.g.,
tail vs. limb) when transplanted to heterotopic locations. Some investigators have noted the regression of blastemas following transplantation
(Morrill, 1921; Uranovsky, 1936; Savchuk, 1938), and it is probable
that this is a more common phenomenon than has generally been
admitted. If so, the development of transplanted blastemas in accordance with their new locations may be explained just as logically by
resorption and replacement with cells from the host site, as by the
complete conversion of a blastema into a new structure of altered
orientation or different kind. These alternative hypotheses have never
been put to the critical test because of technical difficulties in tracing
the exact origins of cells. Garzicic (1926) attempted to distinguish host
and donor tissue by pigmentary differences. Black blastemas from T.
cristatus legs were grafted to the amputated yellow stumps of T.
taeniatus. The resulting regenerates were either black, yellow or of
mixed types, but even if the results were consistent, the presence or
absence of pigment cells is hardly a reliable criterion for judging the
behaviour of other kinds of cells. A different approach to the problem
(Goss, unpublished work) involved the transplantation of tail blastemas
to hind leg stumps which had previously been exposed to regeneration
inhibiting doses of X-rays. In this manner, the limb tissues were
excluded from active participation in regeneration, but might still be
able to influence the morphogenesis of the tail blastema, provided such
effects are not themselves precluded by X-irradiation. None of the
transplanted blastemas developed into limbs. Some of the more advanced
ones became tails, while the others failed to develop altogether.
Although these results do not prove that a tail blastema cannot possibly
develop into a limb, they do support the contention that to do so limb
tissues must become incorporated into the regenerate. Lacking positive
proof to the contrary, the more discretionary view would favour the
117
by Lodyzenskaia (1928) and Abeloos and Lecamp (1931). Whereas limb
blastemas cut off and replaced in their normal orientations developed
into normal regenerates, reimplantation of blastemas after 180° rotation resulted in the production of abnormal regenerates (duplications,
Polydactyly, etc.). Axial conflicts result in abnormalities.
It is logical to interpret these data as indicating that young blastemas
are morphogenetically undetermined and therefore exhibit developmental patterns commensurate with the locations to which they are
transplanted. In contrast, older blastemas are presumably determined
and thus develop as they would had they not been transplanted. In
intermediate cases, both the blastema and the stump may express their
morphogenetic potentialities thus producing abnormal regenerates in
the form of chimerae. Yet it is still not conclusively proved that young,
undetermined blastemas can really develop into alien structures (e.g.,
tail vs. limb) when transplanted to heterotopic locations. Some investigators have noted the regression of blastemas following transplantation
(Morrill, 1921; Uranovsky, 1936; Savchuk, 1938), and it is probable
that this is a more common phenomenon than has generally been
admitted. If so, the development of transplanted blastemas in accordance with their new locations may be explained just as logically by
resorption and replacement with cells from the host site, as by the
complete conversion of a blastema into a new structure of altered
orientation or different kind. These alternative hypotheses have never
been put to the critical test because of technical difficulties in tracing
the exact origins of cells. Garzicic (1926) attempted to distinguish host
and donor tissue by pigmentary differences. Black blastemas from T.
cristatus legs were grafted to the amputated yellow stumps of T.
taeniatus. The resulting regenerates were either black, yellow or of
mixed types, but even if the results were consistent, the presence or
absence of pigment cells is hardly a reliable criterion for judging the
behaviour of other kinds of cells. A different approach to the problem
(Goss, unpublished work) involved the transplantation of tail blastemas
to hind leg stumps which had previously been exposed to regeneration
inhibiting doses of X-rays. In this manner, the limb tissues were
excluded from active participation in regeneration, but might still be
able to influence the morphogenesis of the tail blastema, provided such
effects are not themselves precluded by X-irradiation. None of the
transplanted blastemas developed into limbs. Some of the more advanced
ones became tails, while the others failed to develop altogether.
Although these results do not prove that a tail blastema cannot possibly
develop into a limb, they do support the contention that to do so limb
tissues must become incorporated into the regenerate. Lacking positive
proof to the contrary, the more discretionary view would favour the