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H E N R I E T T E HERLANT-MEEWIS
ing. Such experiments have been made recently on polychaetes by
Casanova (1955), Durchon (1956b, 1960,1961), Clark and Bonney (1960),
Clark and Evans (1961), Hauenschild (1960), Durchon and Marcel (1962)
and on oligochaetes by Hubl (1956), Michon (1962) and Saussey (1963a).
Here again, the results are more complete in polychaetes. For this
reason, we shall examine them first.
In 1955, Casanova experimented on Platynereis assiliensis. In this
species transection between the fifteenth and sixteenth segments is
always followed by caudal regeneration. At the same time as transection
Casanova amputated the prostomium either in front of the anterior
eyes (thus removing the palpi and antennae) or behind the posterior
eyes. He obtained regeneration of palpi and antennae when the prostomium was amputated in front of the anterior eyes but when amputation was behind the posterior eyes, only healing took place; the prostomium was not regenerated. Caudal regeneration was normal in the
case of amputation in front of the anterior eyes but was considerably
delayed in the other case: healing took 12 instead of 7 days and, after
1 month, worms lacking a prostomium had only reconstructed three
segments, whereas controls had twelve segments and were six times as
long. Casanova concluded that the delay in caudal regeneration could
be due to the absence of the brain, which was largely destroyed by the
ablation of the prostomium.
In 1956(b), Durchon repeated these experiments on the same polychaete and on 'atoque' forms of Nereis costae and Perinereis cultrifera.
Worms were transected first through the middle of the body and 24 h
later either the whole prostomium or the brain only was removed. All
worms, including controls, were maintained in a state of inanition.
Worms without a prostomium or brain survived for 1 or 2 months. As
can be seen in Fig. 26, there was a considerable lessening of caudal regenerating power in the absence of a prostomium or of a brain. Durchon
concluded from his experiments that ablation of the prostomium or
brain did not prevent caudal regeneration but limited its potentialities.
In 1960, Clark and Bonney carried out similar experiments on females
of Nereis diversicolor. The worms were transected at the fifth posterior
segment and decerebrated either 24 h before or 72 h after the first
operation. The results obtained 30 days later are shown in Fig. 27. As
we have seen previously, during caudal regeneration scar formation is
followed by reconstruction of a vascularized pygidium ; growth of the
regeneration bud is directed towards the region lying ahead of the new
prostomium. In the controls, nearly all the worms had reconstructed
from one to twelve segments, three of them had only formed a pygidium,
but histological observation showed that mitotic activity was intense in
the zone of growth, indicating that the process had only been delayed.
H E N R I E T T E HERLANT-MEEWIS
ing. Such experiments have been made recently on polychaetes by
Casanova (1955), Durchon (1956b, 1960,1961), Clark and Bonney (1960),
Clark and Evans (1961), Hauenschild (1960), Durchon and Marcel (1962)
and on oligochaetes by Hubl (1956), Michon (1962) and Saussey (1963a).
Here again, the results are more complete in polychaetes. For this
reason, we shall examine them first.
In 1955, Casanova experimented on Platynereis assiliensis. In this
species transection between the fifteenth and sixteenth segments is
always followed by caudal regeneration. At the same time as transection
Casanova amputated the prostomium either in front of the anterior
eyes (thus removing the palpi and antennae) or behind the posterior
eyes. He obtained regeneration of palpi and antennae when the prostomium was amputated in front of the anterior eyes but when amputation was behind the posterior eyes, only healing took place; the prostomium was not regenerated. Caudal regeneration was normal in the
case of amputation in front of the anterior eyes but was considerably
delayed in the other case: healing took 12 instead of 7 days and, after
1 month, worms lacking a prostomium had only reconstructed three
segments, whereas controls had twelve segments and were six times as
long. Casanova concluded that the delay in caudal regeneration could
be due to the absence of the brain, which was largely destroyed by the
ablation of the prostomium.
In 1956(b), Durchon repeated these experiments on the same polychaete and on 'atoque' forms of Nereis costae and Perinereis cultrifera.
Worms were transected first through the middle of the body and 24 h
later either the whole prostomium or the brain only was removed. All
worms, including controls, were maintained in a state of inanition.
Worms without a prostomium or brain survived for 1 or 2 months. As
can be seen in Fig. 26, there was a considerable lessening of caudal regenerating power in the absence of a prostomium or of a brain. Durchon
concluded from his experiments that ablation of the prostomium or
brain did not prevent caudal regeneration but limited its potentialities.
In 1960, Clark and Bonney carried out similar experiments on females
of Nereis diversicolor. The worms were transected at the fifth posterior
segment and decerebrated either 24 h before or 72 h after the first
operation. The results obtained 30 days later are shown in Fig. 27. As
we have seen previously, during caudal regeneration scar formation is
followed by reconstruction of a vascularized pygidium ; growth of the
regeneration bud is directed towards the region lying ahead of the new
prostomium. In the controls, nearly all the worms had reconstructed
from one to twelve segments, three of them had only formed a pygidium,
but histological observation showed that mitotic activity was intense in
the zone of growth, indicating that the process had only been delayed.