128
R. J.
GOSS
ated tails covered by unirradiated limb skin gave rise to limb regenerates.
Conversely, skin from nonregenerating areas of the body when
substituted for the previously removed skin of X-rayed extremities,
fails to bring about regeneration. Following transplantation of skin
from the head (Umanski, 1937) neck (Umanski, 1938a), or flank
(Umanski, 1938a; Trampusch, 1958a) to irradiated limbs, no regeneration occurred. However, pelvic skin (Umanski, 1938a) permitted the
development of abnormal regenerates, presumably by virtue of its
inclusion in the 'limb territory'.
Upon grafting unirradiated tail skin to X-rayed limbs, Umanski
(1937) and Trampusch (1958a) described the production of entirely
tail-like regenerates. Sidorova (1949) also obtained tail regenerates
under similar conditions, but in one case a regenerate possessing three
digits was formed. This apparently resulted from the participation of
normal limb tissues which evidently migrated from more proximal
regions of the leg shielded from the X-rays.
In comparing the activities of skeleton, muscle and skin in affecting
the morphogenesis of regenerates, the experimental results reviewed
above indicate that both bone and muscle, when transplanted to normal
or irradiated structures, can influence the morphogenesis of regenerates
developing after amputation through the treated regions. The effect of
skin, however, depends upon the conditions of the experiment. Thus,
limbs provided with other kinds of skin whether derived from the head,
body or tail, never regenerate anything but limbs. However, X-rayed
limbs similarly covered by foreign skin respond in accordance with the
source of the skin. Head or body skin does not support regeneration,
while tail skin results in the production of tail regenerates. Under these
conditions, the only tissues in the treated region capable of participating
in regeneration are those in the transplant. The ensuing regeneration, if
it occurs, must conform to the morphogenetic influences emanating
from the grafted tissues. Thus, skin can affect morphogenesis if it is the
exclusive source of regeneration material, but not when its participation
in blastema formation is negligible compared with the contribution of
muscle and bone.
Therefore, the three major components of an appendage, bone,
muscle and skin, can, in various circumstances, participate in directing
the morphogenesis of regenerates. To do so, they must presumably
furnish cells for the formation of a blastema. In addition to supplying
their specific cell types (e.g., dedifferentiated muscle fibres, osteoblasts),
all three types of tissue also contribute fibroblasts. Indeed, the latter
cell is undoubtedly capable of mediating morphogenesis. In the case of
skin, it is the principal kind of cell contributed to the blastema and
hence it is responsible for the expression of morphogenetic effects by
R. J.
GOSS
ated tails covered by unirradiated limb skin gave rise to limb regenerates.
Conversely, skin from nonregenerating areas of the body when
substituted for the previously removed skin of X-rayed extremities,
fails to bring about regeneration. Following transplantation of skin
from the head (Umanski, 1937) neck (Umanski, 1938a), or flank
(Umanski, 1938a; Trampusch, 1958a) to irradiated limbs, no regeneration occurred. However, pelvic skin (Umanski, 1938a) permitted the
development of abnormal regenerates, presumably by virtue of its
inclusion in the 'limb territory'.
Upon grafting unirradiated tail skin to X-rayed limbs, Umanski
(1937) and Trampusch (1958a) described the production of entirely
tail-like regenerates. Sidorova (1949) also obtained tail regenerates
under similar conditions, but in one case a regenerate possessing three
digits was formed. This apparently resulted from the participation of
normal limb tissues which evidently migrated from more proximal
regions of the leg shielded from the X-rays.
In comparing the activities of skeleton, muscle and skin in affecting
the morphogenesis of regenerates, the experimental results reviewed
above indicate that both bone and muscle, when transplanted to normal
or irradiated structures, can influence the morphogenesis of regenerates
developing after amputation through the treated regions. The effect of
skin, however, depends upon the conditions of the experiment. Thus,
limbs provided with other kinds of skin whether derived from the head,
body or tail, never regenerate anything but limbs. However, X-rayed
limbs similarly covered by foreign skin respond in accordance with the
source of the skin. Head or body skin does not support regeneration,
while tail skin results in the production of tail regenerates. Under these
conditions, the only tissues in the treated region capable of participating
in regeneration are those in the transplant. The ensuing regeneration, if
it occurs, must conform to the morphogenetic influences emanating
from the grafted tissues. Thus, skin can affect morphogenesis if it is the
exclusive source of regeneration material, but not when its participation
in blastema formation is negligible compared with the contribution of
muscle and bone.
Therefore, the three major components of an appendage, bone,
muscle and skin, can, in various circumstances, participate in directing
the morphogenesis of regenerates. To do so, they must presumably
furnish cells for the formation of a blastema. In addition to supplying
their specific cell types (e.g., dedifferentiated muscle fibres, osteoblasts),
all three types of tissue also contribute fibroblasts. Indeed, the latter
cell is undoubtedly capable of mediating morphogenesis. In the case of
skin, it is the principal kind of cell contributed to the blastema and
hence it is responsible for the expression of morphogenetic effects by