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R. J.
GOSS
regenerating region of the body or to an appendage capable of regeneration. If transplanted to another stump, it makes a difference whether or
not the host appendage is the same kind as that which gave rise to the
blastema. Furthermore, the axial relationships between the blastema
transplant and the stump are of importance, for rotation of the blastema,
or its transplantation to a different level on an appendage, are significant
factors in determining its morphogenetic potentialities.
Blastemas grown in the absence of stump tissues usually do not
undergo any marked development. When cultured in vitro young
blastemas grow more rapidly than older ones in chick embryo juice,
but in Holtfreter's solution explanted regeneration blastemas of all ages
fail to grow (Lecamp, 1947). Older regenerates in tissue culture tend to
dedifferentiate (Lecamp, 1948). Blastemas transplanted to the body
cavity may exhibit chondrogenesis and myogenesis (Waddington, 1940),
but fail to develop into limbs (Monroy & Oddo, 1944). When leg or tail
blastemas were transplanted into lentectomized eyes, Schotte and
Hummel (1939) claimed that the blastema cells differentiated into new
lenses and thus concluded that regenerating tissues were multipotent.
However, the course of development pursued by a transplanted
blastema is markedly affected by the presence or absence of its older
stump tissues. Blastemas transplanted to non-regenerative sites (e.g.,
back or side) usually fail to develop, or at best become undifferentiated
outgrowths. However, when blastemas are similarly grafted with part
of the older stump tissues attached, they prove capable of differentiation
which is always in accordance with their associated stump tissues (de
Giorgi and Guyénot, 1923; de Giorgi, 1924; Milojevic, 1924; Milojevic
and Grbic, 1926; Polezhaev, 1937; Liosner, 1938). It would seem to
follow from this that blastemas transplanted to other kinds of appendages, or back onto their own appendages but in different orientations,
would be expected to develop according to their new associations.
However, it has been demonstrated that the developmental direction a
blastema follows depends in large part on its age. Milojevic (1924) and
Milojevic and Grbic (1926) showed that forelimb blastemas of Triturus,
when transplanted to the cut stumps of hind limbs, developed as hind
limbs (ortsgemass) if they were less than 9 days old, but became
forelimbs (herkunftgemass) if they were more than 12 days old. Between
these two ages, the blastema presumably becomes determined. Weiss
(1927) obtained similar results with tail blastemas transplanted to the
forelimb regions of newts. Younger blastemas developed into limbs,
older ones into tails. Comparable experiments in lizards (Weiss, 1930)
resulted in the growth of tails from older transplanted tail blastemas,
but younger ones failed to grow at all. Further experiments along these
lines, involving the rotation of transplanted blastemas, were carried out
R. J.
GOSS
regenerating region of the body or to an appendage capable of regeneration. If transplanted to another stump, it makes a difference whether or
not the host appendage is the same kind as that which gave rise to the
blastema. Furthermore, the axial relationships between the blastema
transplant and the stump are of importance, for rotation of the blastema,
or its transplantation to a different level on an appendage, are significant
factors in determining its morphogenetic potentialities.
Blastemas grown in the absence of stump tissues usually do not
undergo any marked development. When cultured in vitro young
blastemas grow more rapidly than older ones in chick embryo juice,
but in Holtfreter's solution explanted regeneration blastemas of all ages
fail to grow (Lecamp, 1947). Older regenerates in tissue culture tend to
dedifferentiate (Lecamp, 1948). Blastemas transplanted to the body
cavity may exhibit chondrogenesis and myogenesis (Waddington, 1940),
but fail to develop into limbs (Monroy & Oddo, 1944). When leg or tail
blastemas were transplanted into lentectomized eyes, Schotte and
Hummel (1939) claimed that the blastema cells differentiated into new
lenses and thus concluded that regenerating tissues were multipotent.
However, the course of development pursued by a transplanted
blastema is markedly affected by the presence or absence of its older
stump tissues. Blastemas transplanted to non-regenerative sites (e.g.,
back or side) usually fail to develop, or at best become undifferentiated
outgrowths. However, when blastemas are similarly grafted with part
of the older stump tissues attached, they prove capable of differentiation
which is always in accordance with their associated stump tissues (de
Giorgi and Guyénot, 1923; de Giorgi, 1924; Milojevic, 1924; Milojevic
and Grbic, 1926; Polezhaev, 1937; Liosner, 1938). It would seem to
follow from this that blastemas transplanted to other kinds of appendages, or back onto their own appendages but in different orientations,
would be expected to develop according to their new associations.
However, it has been demonstrated that the developmental direction a
blastema follows depends in large part on its age. Milojevic (1924) and
Milojevic and Grbic (1926) showed that forelimb blastemas of Triturus,
when transplanted to the cut stumps of hind limbs, developed as hind
limbs (ortsgemass) if they were less than 9 days old, but became
forelimbs (herkunftgemass) if they were more than 12 days old. Between
these two ages, the blastema presumably becomes determined. Weiss
(1927) obtained similar results with tail blastemas transplanted to the
forelimb regions of newts. Younger blastemas developed into limbs,
older ones into tails. Comparable experiments in lizards (Weiss, 1930)
resulted in the growth of tails from older transplanted tail blastemas,
but younger ones failed to grow at all. Further experiments along these
lines, involving the rotation of transplanted blastemas, were carried out