REGENERATION IN ANNELIDS
173
blast activation and in multiplication of the neurilemmal cells, as
observed by us in Eisenia after decapitation. Moreover, it is known that
in blastemas of limb regeneration, nerve fibre ramifications grow into
the healing epithelium where they end in swellings which are closely
applied to the cell membranes. Ultramicroscopic examination has
shown that at these points of contact there are small vesicles which
closely resemble those seen in synaptic systems. They might contain
a chemical mediator whose action is limited to the cells in contact with
the nerve endings.
According to Singer and Craven (1948) this substance would be
acetylcholine which could play a trophic role and exert a positive influence on protein synthesis. Indeed, it has been shown by autoradiography that incorporation of radioactive methionine reaches maximal
intensity in proteins synthesized near the nerve endings. In oligochaetes,
similar nerve fibres have been seen to penetrate the ectoderm in a
similar way, and we have seen that if this did not occur the ectodermal
cicatricial cells remained incapable of dedifferentiation. In Polydora
flava, Thouveny (1958a) laid emphasis on the role of the nervous system
in epidermal dedifferentiation and subsequent RNA synthesis. The
trophic action described for amphibians is thought by Massaro and
Schrank (1959) to apply in the case of oligochaetes. These authors have
shown that lithium chloride inhibits regeneration by acting as a
nervous depressant and that its influence is specific for certain stages,
such as during the release and migration of neoblasts along the nerve
cord, and blastemal cell differentiation. Although neoblasts were first
discovered in annelids (Randolph, 1892) and have been described in
several species of oligochaetes, at present very little is known of the
biochemical and enzymatic mechanisms involved in their transformations.
In Eisenia foetida, Powell (1951) reported an increase in the alkaline
glycerophosphatase content of the integument adjacent to the wound,
immediately after transection. Under the same conditions, Needham
(1962) found that the content of arginase increased in cells of the
digestive tract of Lumbricus. Activation of migrating neoblasts and of
ecto- and endodermal blastocytes is followed by an increase in the
RNA content of the cells. This increase in the RNA content of the
neoblasts probably involves important ergastoplasmic development
which should be confirmed by electron microscopy.
In oligochaetes, Massaro and Schrank (1959) have demonstrated the
inhibitory action of barbituric acid on regeneration. In Eisenia foetida
this inhibition is particularly marked from the 7th to the 12th day after
amputation, a period which coincides with the last stages of blastema
formation. I t is also known that X-rays do not affect synthetic processes
173
blast activation and in multiplication of the neurilemmal cells, as
observed by us in Eisenia after decapitation. Moreover, it is known that
in blastemas of limb regeneration, nerve fibre ramifications grow into
the healing epithelium where they end in swellings which are closely
applied to the cell membranes. Ultramicroscopic examination has
shown that at these points of contact there are small vesicles which
closely resemble those seen in synaptic systems. They might contain
a chemical mediator whose action is limited to the cells in contact with
the nerve endings.
According to Singer and Craven (1948) this substance would be
acetylcholine which could play a trophic role and exert a positive influence on protein synthesis. Indeed, it has been shown by autoradiography that incorporation of radioactive methionine reaches maximal
intensity in proteins synthesized near the nerve endings. In oligochaetes,
similar nerve fibres have been seen to penetrate the ectoderm in a
similar way, and we have seen that if this did not occur the ectodermal
cicatricial cells remained incapable of dedifferentiation. In Polydora
flava, Thouveny (1958a) laid emphasis on the role of the nervous system
in epidermal dedifferentiation and subsequent RNA synthesis. The
trophic action described for amphibians is thought by Massaro and
Schrank (1959) to apply in the case of oligochaetes. These authors have
shown that lithium chloride inhibits regeneration by acting as a
nervous depressant and that its influence is specific for certain stages,
such as during the release and migration of neoblasts along the nerve
cord, and blastemal cell differentiation. Although neoblasts were first
discovered in annelids (Randolph, 1892) and have been described in
several species of oligochaetes, at present very little is known of the
biochemical and enzymatic mechanisms involved in their transformations.
In Eisenia foetida, Powell (1951) reported an increase in the alkaline
glycerophosphatase content of the integument adjacent to the wound,
immediately after transection. Under the same conditions, Needham
(1962) found that the content of arginase increased in cells of the
digestive tract of Lumbricus. Activation of migrating neoblasts and of
ecto- and endodermal blastocytes is followed by an increase in the
RNA content of the cells. This increase in the RNA content of the
neoblasts probably involves important ergastoplasmic development
which should be confirmed by electron microscopy.
In oligochaetes, Massaro and Schrank (1959) have demonstrated the
inhibitory action of barbituric acid on regeneration. In Eisenia foetida
this inhibition is particularly marked from the 7th to the 12th day after
amputation, a period which coincides with the last stages of blastema
formation. I t is also known that X-rays do not affect synthetic processes