144
R. J.
GOSS
into the regeneration of reversed limbs (Gräper, 1922; Milojevic and
Grbic, 1925; Burchardt, 1930; Belkin, 1934a, c, d; Butler, 1949, 1951,
1955; Dent, 1950,1954; Deck and Riley, 1958). Indeed, some experimenters have reported the simultaneous regeneration from both proximal
and distal stumps of limb segments (Belkin, 1934e; Monroy, 1941, 1942;
Korobova, 1947; Umanski and Kudokotzev, 1951). Although regeneration after the reversal of limb polarity may be absent or very abortive
(Weber, 1926; Belkin, 1934b), or may result in abnormal or duplicated
limbs (Savchuk, 1937), the structure usually produced is a normal distal
appendage. Thus, if the distal end of a limb is grafted elsewhere on the
body, and the exposed stump is what was originally the proximal end
of the extremity, there will regenerate a new limb which is essentially a
mirror image of the stump. Even the pattern of innervation closely
resembles that in normal limb regenerates (Deck, 1955). Indeed, it has
been shown that this kind of regeneration, like that from normally
polarized stumps, depends upon adequate innervation, and that grafted
limbs often regress until invaded by sufficient new fibres to promote
their regeneration (Butler, 1955). Dent (1950, 1954) has demonstrated
that the regeneration of reversed limb grafts can be expedited by
deviating nerves to them.
As in limbs, other vertebrate structures can also be induced to
regenerate in proximal directions. Harrison (1898) and Korobova (1948)
succeeded in grafting tail buds of anuran embryos together, and later
separated the parabionts by transverse cuts through the tail of one of
the tadpoles. Hence, the remaining animal had its former partner's tail
grafted to its own, but attached by the distal end. Such reversed tails,
according to Harrison (1898), gave rise to distally tapering regenerates
with myotomes irregularly oriented but unmistakably exhibiting a
normal distally directed polarity. Korobova (1948) reported that
although the tail as a whole tapered distally, its myotomes did not
point proximally as would be expected in a normally oriented tail. Thus,
according to their over-all shapes the tails regenerated distally but
they regenerated proximally with reference to their myotomes. Other
experiments on the regeneration of reversed tails were performed by
Milojevic and Burian (1926). These authors transplanted sections of
Triturus tails upside down to the back and obtained regenerates which
were normally oriented instead of inverted. However, in view of the
inconclusive nature of the general work on the regeneration of reversed
tails, further studies are in order. Of especial value would be a detailed
analysis of the histology of regenerates from tails of reversed polarity,
with particular reference to the histology of regenerating spinal cords
in such tails.
In the fins of fishes, regeneration in a proximal direction sometimes
R. J.
GOSS
into the regeneration of reversed limbs (Gräper, 1922; Milojevic and
Grbic, 1925; Burchardt, 1930; Belkin, 1934a, c, d; Butler, 1949, 1951,
1955; Dent, 1950,1954; Deck and Riley, 1958). Indeed, some experimenters have reported the simultaneous regeneration from both proximal
and distal stumps of limb segments (Belkin, 1934e; Monroy, 1941, 1942;
Korobova, 1947; Umanski and Kudokotzev, 1951). Although regeneration after the reversal of limb polarity may be absent or very abortive
(Weber, 1926; Belkin, 1934b), or may result in abnormal or duplicated
limbs (Savchuk, 1937), the structure usually produced is a normal distal
appendage. Thus, if the distal end of a limb is grafted elsewhere on the
body, and the exposed stump is what was originally the proximal end
of the extremity, there will regenerate a new limb which is essentially a
mirror image of the stump. Even the pattern of innervation closely
resembles that in normal limb regenerates (Deck, 1955). Indeed, it has
been shown that this kind of regeneration, like that from normally
polarized stumps, depends upon adequate innervation, and that grafted
limbs often regress until invaded by sufficient new fibres to promote
their regeneration (Butler, 1955). Dent (1950, 1954) has demonstrated
that the regeneration of reversed limb grafts can be expedited by
deviating nerves to them.
As in limbs, other vertebrate structures can also be induced to
regenerate in proximal directions. Harrison (1898) and Korobova (1948)
succeeded in grafting tail buds of anuran embryos together, and later
separated the parabionts by transverse cuts through the tail of one of
the tadpoles. Hence, the remaining animal had its former partner's tail
grafted to its own, but attached by the distal end. Such reversed tails,
according to Harrison (1898), gave rise to distally tapering regenerates
with myotomes irregularly oriented but unmistakably exhibiting a
normal distally directed polarity. Korobova (1948) reported that
although the tail as a whole tapered distally, its myotomes did not
point proximally as would be expected in a normally oriented tail. Thus,
according to their over-all shapes the tails regenerated distally but
they regenerated proximally with reference to their myotomes. Other
experiments on the regeneration of reversed tails were performed by
Milojevic and Burian (1926). These authors transplanted sections of
Triturus tails upside down to the back and obtained regenerates which
were normally oriented instead of inverted. However, in view of the
inconclusive nature of the general work on the regeneration of reversed
tails, further studies are in order. Of especial value would be a detailed
analysis of the histology of regenerates from tails of reversed polarity,
with particular reference to the histology of regenerating spinal cords
in such tails.
In the fins of fishes, regeneration in a proximal direction sometimes