REGENERATION IN ANNELIDS
211
the regenerated segments, generally limited in number, the cephalic
organs are differentiated.
Regular regeneration will not be realized unless all these conditions
are met. Each of them depends on a number of factors. Among them,
we have brought into focus the known facts concerning the influence of
the nervous system.
Many experiments have demonstrated that the presence of the
nervous system at the point of healing is absolutely indispensable for
regeneration to occur. However, it does not seem necessary for the
nerve cord to remain intact ; it is sufficient for a number of regenerating
nerve fibres to penetrate the cicatricial ectoderm for the latter to continue its activation process.
Finally, the discovery of neurosecretory phenomena has shown how
important the nervous system is in hormonal regulation mechanisms.
The endocrine role of the nervous system in regeneration has been
demonstrated by extirpation and grafting of nerve fragments in Polychaetae as well as in Oligochaetae. Neurosecretory cells have been
described in ganglia of several annelid species, but the nature of the
secretory substances elaborated by these cells and the role played by
them when released into the blood stream in regeneration are not yet
understood. At present, it is known that for pygidial regeneration to
take place, the brain must be present during the first few days following
transection, a period coinciding with healing and arrangment of regenerative elements in the blastema; hyperactivity of some of the
neurosecretory cells in the brain can then be observed. A relation between diapause and the faculty of caudal regeneration has been noted
by some investigators. When a worm enters diapause, feeding and
ovulation stop, and the reproductive organs begin to regress. During
these processes, several types of neurosecretory cells, located in the
ventral ganglia, are activated. It seems probable from these observations that two hormones are secreted by different neurosecretory cells,
perhaps antagonistic to one another—one participating in sexual reproduction, the other in regeneration and possibly in asexual reproduction.
Whatever the case may be, endocrinological phenomena are open to
further investigation in the field of annelid regeneration.
References
Abeloos, M. (1949). Bull. Soc. zool. Fr. 74, 95.
Abeloos, M. (1950a). C. R. Acad. Sei., Paris 230, 477.
Abeloos, M. (1950b). C. R. Acad. Sei., Paris 230, 1109.
Abeloos, M. (1950c). C. R. Acad. Sei., Paris 230, 1899,
Abeloos, M. (1952). C. R. Soc. Biol., Paris 146, 1750,
Abeloos, M. (1953). C. R. Soc. Biol, Paris 147, 436.
211
the regenerated segments, generally limited in number, the cephalic
organs are differentiated.
Regular regeneration will not be realized unless all these conditions
are met. Each of them depends on a number of factors. Among them,
we have brought into focus the known facts concerning the influence of
the nervous system.
Many experiments have demonstrated that the presence of the
nervous system at the point of healing is absolutely indispensable for
regeneration to occur. However, it does not seem necessary for the
nerve cord to remain intact ; it is sufficient for a number of regenerating
nerve fibres to penetrate the cicatricial ectoderm for the latter to continue its activation process.
Finally, the discovery of neurosecretory phenomena has shown how
important the nervous system is in hormonal regulation mechanisms.
The endocrine role of the nervous system in regeneration has been
demonstrated by extirpation and grafting of nerve fragments in Polychaetae as well as in Oligochaetae. Neurosecretory cells have been
described in ganglia of several annelid species, but the nature of the
secretory substances elaborated by these cells and the role played by
them when released into the blood stream in regeneration are not yet
understood. At present, it is known that for pygidial regeneration to
take place, the brain must be present during the first few days following
transection, a period coinciding with healing and arrangment of regenerative elements in the blastema; hyperactivity of some of the
neurosecretory cells in the brain can then be observed. A relation between diapause and the faculty of caudal regeneration has been noted
by some investigators. When a worm enters diapause, feeding and
ovulation stop, and the reproductive organs begin to regress. During
these processes, several types of neurosecretory cells, located in the
ventral ganglia, are activated. It seems probable from these observations that two hormones are secreted by different neurosecretory cells,
perhaps antagonistic to one another—one participating in sexual reproduction, the other in regeneration and possibly in asexual reproduction.
Whatever the case may be, endocrinological phenomena are open to
further investigation in the field of annelid regeneration.
References
Abeloos, M. (1949). Bull. Soc. zool. Fr. 74, 95.
Abeloos, M. (1950a). C. R. Acad. Sei., Paris 230, 477.
Abeloos, M. (1950b). C. R. Acad. Sei., Paris 230, 1109.
Abeloos, M. (1950c). C. R. Acad. Sei., Paris 230, 1899,
Abeloos, M. (1952). C. R. Soc. Biol., Paris 146, 1750,
Abeloos, M. (1953). C. R. Soc. Biol, Paris 147, 436.