REGENERATION IN ANNELIDS
209
To conclude, experiments which seem to prove that the nervous
system has a hormonal function in regeneration could be explained by
means of available histological data in the following manner : any operation performed on an annelid and pertaining to its nervous system, such
as transection of the ventral cord or ganglion ablation, determines
hormonal imbalance leading to the temporary accumulation of the
neurosecretory substances in some cells. This block would be instantaneous and would persist during wound-healing and blastema formation. The neurosecretory cells would then discharge the accumulated
substance into the repaired circulatory system so that secretory substances would reach the regenerating regions, but it is still not known
how they would act at this level.
VI. General Conclusions
In this study, we have attempted to bring up to date the present
conception of the origin of the regenerative bud and of the conditions
that determine its development in a cephalic or caudal region.
1. The first of these conditions is the presence, at the amputation
surface, of cells in an embryonic state or likely to revert to that state.
In this respect, Oligochaetae are certainly more privileged than Polychaetae ; as a rule tissue differentiation is not as complete in oligochaetes
and they have more replacement cells. These factors characterize the
organisms likely to regenerate more easily and especially the asexuallyreproducing annelids. These worms have a reserve of blastogenetic
elements ready to multiply during fissiparity or budding. The presence
in some worms of mesodermal neoblasts likely to migrate towards a
region of regeneration has long been known, but it is only recently that
cell migration has actually been shown to occur. This has been done by
counting the neoblasts in different regions at various stages and by
localized X-irradiation.
2. The second condition is the release of a substance or substances
likely to stimulate the transformation of regenerative elements and their
possible migration and multiplication. These mechanisms are as yet not
sufficiently well defined in Oligochaetae. The initiating factor in activation and migration of neoblasts has been ascribed to injury at transection but these phenomena can also occur without intervention, for
example, during induction of a fissiparity zone in some Naidae, or, as
was shown by Stephan-Dubois, long after healing in segments remote
from the healing zone. In respect of injury, the intervention of mediators,
necrotic hormones or substances released by degenerating or regenerating
nerve fibres, have been considered. The many parts played by various
209
To conclude, experiments which seem to prove that the nervous
system has a hormonal function in regeneration could be explained by
means of available histological data in the following manner : any operation performed on an annelid and pertaining to its nervous system, such
as transection of the ventral cord or ganglion ablation, determines
hormonal imbalance leading to the temporary accumulation of the
neurosecretory substances in some cells. This block would be instantaneous and would persist during wound-healing and blastema formation. The neurosecretory cells would then discharge the accumulated
substance into the repaired circulatory system so that secretory substances would reach the regenerating regions, but it is still not known
how they would act at this level.
VI. General Conclusions
In this study, we have attempted to bring up to date the present
conception of the origin of the regenerative bud and of the conditions
that determine its development in a cephalic or caudal region.
1. The first of these conditions is the presence, at the amputation
surface, of cells in an embryonic state or likely to revert to that state.
In this respect, Oligochaetae are certainly more privileged than Polychaetae ; as a rule tissue differentiation is not as complete in oligochaetes
and they have more replacement cells. These factors characterize the
organisms likely to regenerate more easily and especially the asexuallyreproducing annelids. These worms have a reserve of blastogenetic
elements ready to multiply during fissiparity or budding. The presence
in some worms of mesodermal neoblasts likely to migrate towards a
region of regeneration has long been known, but it is only recently that
cell migration has actually been shown to occur. This has been done by
counting the neoblasts in different regions at various stages and by
localized X-irradiation.
2. The second condition is the release of a substance or substances
likely to stimulate the transformation of regenerative elements and their
possible migration and multiplication. These mechanisms are as yet not
sufficiently well defined in Oligochaetae. The initiating factor in activation and migration of neoblasts has been ascribed to injury at transection but these phenomena can also occur without intervention, for
example, during induction of a fissiparity zone in some Naidae, or, as
was shown by Stephan-Dubois, long after healing in segments remote
from the healing zone. In respect of injury, the intervention of mediators,
necrotic hormones or substances released by degenerating or regenerating
nerve fibres, have been considered. The many parts played by various