164
HENRIETTE HERLANT-MEEWIS
possible. Neoblast sensitivity to X-rays was the starting point in the
application of the local irradiation technique devised by Wolff (1936).
First used on planarians by Dubois (1949), it was then extended to
annelids to prove the reality of neoblast migration during regeneration
phenomena. Simultaneously, Foulkes (1953) and Stephan-Dubois (1954)
applied the technique, the former for the study of cephalic regeneration
in Aulophorus furcatus, the latter to study posterior regeneration in
several Oligochaetae and then in Nereis diversicolor (1958). The technique
involves X-irradiation of a number of segments of the worm (the number
of segments varies) followed by transection within the irradiated zone.
Foulkes observed three series of Aulophorus. One was not irradiated,
another received a total of 2,600 r on the whole body, and the third the
same dose on the 18-21 anterior segments. The head was amputated at
the 6th segment immediately after exposure. In non-irradiated controls
3-6 h after decapitation, the regeneration blastema contained neoblasts
which had migrated from posterior segments. According to Foulkes,
these neoblasts condition the thickening and proliferation of the healing
ectoderm as well as endodermal regeneration. They also give rise to
mesodermal formations. The head is completely regenerated after 5
days. In totally irradiated worms no regeneration occurred, the animals
dying within 14r-21 days of exposure. Worms irradiated anteriorly
reconstructed the cephalic segments normally but after some delay.
Irradiation had destroyed the neoblasts in the region treated and had
also prevented new mesodermal cells from changing into neoblasts in
this region. Nevertheless, 6 h after transection, the irradiated segments
contained neoblasts derived from non-irradiated posterior segments.
To reach the blastema, they must have been capable of migrating the
entire length of 15 segments. In this way, Foulkes proved that neoblasts
can also migrate from the hind end towards the front end. This forward
migration had been observed previously by Turner (1935) and StephanDubois (1956); it had earlier been denied by Stone (1933) working on
T. tubifex and by O'Brien (1942) studying Nais paraguayensis. It seems,
therefore, that this phenomenon cannot be generalized.
Stephan-Dubois studied caudal regeneration in Lumbriculus variegatus, Tubifex tubifex and Enchytraeus albidus following X-irradiation.
Three to four hours after irradiation, the worms were transected so as
to leave two to four irradiated segments. Amputation triggered neoblast
transformation along nine to ten segments in Lumbriculus and two to
three in Tubifex. As we have seen, neoblasts from irradiated segments
are activated and undergo development to some extent but later nuclear
disintegration takes place and they disappear. Neoblasts in the nonirradiated, more anterior segments, on the other hand, evolve normally
and migrate backwards through the irradiated segments. This migration
HENRIETTE HERLANT-MEEWIS
possible. Neoblast sensitivity to X-rays was the starting point in the
application of the local irradiation technique devised by Wolff (1936).
First used on planarians by Dubois (1949), it was then extended to
annelids to prove the reality of neoblast migration during regeneration
phenomena. Simultaneously, Foulkes (1953) and Stephan-Dubois (1954)
applied the technique, the former for the study of cephalic regeneration
in Aulophorus furcatus, the latter to study posterior regeneration in
several Oligochaetae and then in Nereis diversicolor (1958). The technique
involves X-irradiation of a number of segments of the worm (the number
of segments varies) followed by transection within the irradiated zone.
Foulkes observed three series of Aulophorus. One was not irradiated,
another received a total of 2,600 r on the whole body, and the third the
same dose on the 18-21 anterior segments. The head was amputated at
the 6th segment immediately after exposure. In non-irradiated controls
3-6 h after decapitation, the regeneration blastema contained neoblasts
which had migrated from posterior segments. According to Foulkes,
these neoblasts condition the thickening and proliferation of the healing
ectoderm as well as endodermal regeneration. They also give rise to
mesodermal formations. The head is completely regenerated after 5
days. In totally irradiated worms no regeneration occurred, the animals
dying within 14r-21 days of exposure. Worms irradiated anteriorly
reconstructed the cephalic segments normally but after some delay.
Irradiation had destroyed the neoblasts in the region treated and had
also prevented new mesodermal cells from changing into neoblasts in
this region. Nevertheless, 6 h after transection, the irradiated segments
contained neoblasts derived from non-irradiated posterior segments.
To reach the blastema, they must have been capable of migrating the
entire length of 15 segments. In this way, Foulkes proved that neoblasts
can also migrate from the hind end towards the front end. This forward
migration had been observed previously by Turner (1935) and StephanDubois (1956); it had earlier been denied by Stone (1933) working on
T. tubifex and by O'Brien (1942) studying Nais paraguayensis. It seems,
therefore, that this phenomenon cannot be generalized.
Stephan-Dubois studied caudal regeneration in Lumbriculus variegatus, Tubifex tubifex and Enchytraeus albidus following X-irradiation.
Three to four hours after irradiation, the worms were transected so as
to leave two to four irradiated segments. Amputation triggered neoblast
transformation along nine to ten segments in Lumbriculus and two to
three in Tubifex. As we have seen, neoblasts from irradiated segments
are activated and undergo development to some extent but later nuclear
disintegration takes place and they disappear. Neoblasts in the nonirradiated, more anterior segments, on the other hand, evolve normally
and migrate backwards through the irradiated segments. This migration