174
H E N R I E T T E HERLANT-MEEWIS
within the cytoplasm but act essentially on the multiplication of these
cells.
Finally, in other worm groups, especially in planarians, Clement-Noel
(1944) has shown that neoblasts contain RNA and Pedersen (1959) has
shown that thiolprotein is also present. Brächet and his associates
(Brächet and Delange-Cornil, 1958; Brächet, 1959; Descotils-Heernu
et al., 1961) have laid emphasis on the role of —SH and —S—S—
bonds in morphogenesis. They consider that a 0-001 M solution of
j8-mercapto-ethanol acts on regeneration by modifying the intracellular
thiol-disulphide equilibrium but has no effect on RNA synthesis. It
also slows down cell division. Gabriel (1963) also showed that mercaptoethanol does not prevent neoblasts from undergoing changes, i.e. from
increasing their RNA content and migrating ; a regeneration blastema
can appear but will not continue to evolve. By applying the treatment
at different stages and varying its duration, Gabriel tried to demonstrate
that mercapto-ethanol probably acts on the biochemical mechanisms
stimulating differentiation; it would not act directly on the enzymatic
systems of the cells, but rather on the inductive and inhibitory substances which play a part in tissue differentiation during regeneration.
O'Brien (1946) pointed out that at the time of differentiation the regeneration blastema in Nais paraguayensis is the site of glycolysis: substances such as iodoacetic acid, which inhibits phosphoglyceraldehyde
dehydrogenase, prevent the development of the regeneration bud.
Among annelids, the limicolous oligochaetes seem well suited to fuller
investigation of these problems. During asexual reproduction, blastocytes from various sources actively participate in the zones of fissiparity
or of pygidial budding and growth of the new zooids is very rapid. In
order to study the effects of various inhibitory substances on activation
and dedifferentiation and on subsequent differentiation and growth, it
would be easy enough in these cases to dissociate the former process
from the latter. Moreover, it is possible in some species to predict how
the zooids which constitute the chain will appear (Meewis, 1933;
Herlant-Meewis, 1950,1951) and it would be easy to detect abnormalities
in development.
C. Role of the Nervous System
1. Caudal and Cephalic Regeneration
As early as 1902, Morgan carried out the now classical experiments on
Eisenia foetida, showing that the presence of the ventral nerve cord in
the cephalic region was essential for head regeneration to occur. Thus,
in the experiment diagrammatically represented in Fig. 14A, when the
nerve cord was completely destroyed along the five segments adjacent
H E N R I E T T E HERLANT-MEEWIS
within the cytoplasm but act essentially on the multiplication of these
cells.
Finally, in other worm groups, especially in planarians, Clement-Noel
(1944) has shown that neoblasts contain RNA and Pedersen (1959) has
shown that thiolprotein is also present. Brächet and his associates
(Brächet and Delange-Cornil, 1958; Brächet, 1959; Descotils-Heernu
et al., 1961) have laid emphasis on the role of —SH and —S—S—
bonds in morphogenesis. They consider that a 0-001 M solution of
j8-mercapto-ethanol acts on regeneration by modifying the intracellular
thiol-disulphide equilibrium but has no effect on RNA synthesis. It
also slows down cell division. Gabriel (1963) also showed that mercaptoethanol does not prevent neoblasts from undergoing changes, i.e. from
increasing their RNA content and migrating ; a regeneration blastema
can appear but will not continue to evolve. By applying the treatment
at different stages and varying its duration, Gabriel tried to demonstrate
that mercapto-ethanol probably acts on the biochemical mechanisms
stimulating differentiation; it would not act directly on the enzymatic
systems of the cells, but rather on the inductive and inhibitory substances which play a part in tissue differentiation during regeneration.
O'Brien (1946) pointed out that at the time of differentiation the regeneration blastema in Nais paraguayensis is the site of glycolysis: substances such as iodoacetic acid, which inhibits phosphoglyceraldehyde
dehydrogenase, prevent the development of the regeneration bud.
Among annelids, the limicolous oligochaetes seem well suited to fuller
investigation of these problems. During asexual reproduction, blastocytes from various sources actively participate in the zones of fissiparity
or of pygidial budding and growth of the new zooids is very rapid. In
order to study the effects of various inhibitory substances on activation
and dedifferentiation and on subsequent differentiation and growth, it
would be easy enough in these cases to dissociate the former process
from the latter. Moreover, it is possible in some species to predict how
the zooids which constitute the chain will appear (Meewis, 1933;
Herlant-Meewis, 1950,1951) and it would be easy to detect abnormalities
in development.
C. Role of the Nervous System
1. Caudal and Cephalic Regeneration
As early as 1902, Morgan carried out the now classical experiments on
Eisenia foetida, showing that the presence of the ventral nerve cord in
the cephalic region was essential for head regeneration to occur. Thus,
in the experiment diagrammatically represented in Fig. 14A, when the
nerve cord was completely destroyed along the five segments adjacent