200
H E N R I E T T E HERLANT-MEEWIS
In worms decerebrated before posterior section (Fig. 27A) no regeneration had occurred. After 30 days the worms had either healed or had
formed a pygidium again, but the lack of mitotic activity indicated no
further development. In worms decerebrated 3 days after transection
(Fig. 27B), three out of nineteen had regenerated one segment, the
others had healed or had only formed a pygidium. Clark and Bonney
concluded from their experiments that the brain plays an essential part
during the first stages of regeneration but later its presence is less
important.
For a better understanding of the brain's essential role, Clark and
Evans (1961) varied the interval between the two operations, from 30
min to 7 days. The results were the same when the two operations were
no more than 48 h apart (Fig. 28) ; the worms healed and could reconstruct a pygidium. Vascularization of the pygidium which precedes
formation of a regeneration bud, took place only when decerebration
was performed 4 days after transection. Finally, when the two operations were more than 5 days apart, regeneration occurred in a number of
cases but was considerably retarded. From these experiments, Clark
and Evans concluded that discharge of hormones into the circulation
does not begin immediately after transection ; for 3-4 days, the hormones
are stored in the brain, and if the cerebral ganglia are removed during
this period hormonal discharge cannot take place. From the 4th day
onwards, secretion of the hormonal substance begins. I t will depend on
the amount of hormone in the blood at the time of decerebration, to
what extent regeneration will be delayed or inhibited. Graft experiments have confirmed these results (Fig. 29). The brain was removed
from a worm immediately after posterior transection and was implanted
or injected as an extract into the coelomic cavity of another decerebrated worm. Neither recipient nor donor regenerated posteriorly under
those circumstances ; presumably the graft did not contain the hormones
needed for regeneration. However, if the donor's brain was removed 2-3
days after posterior transection and was then grafted in an amputated
recipient, the latter regenerated normally but the donor did not : at that
particular time the donor's brain had stored the hormone and had been
activated. Finally, if the donor's brain was taken out 4 days after
posterior transection, alternative results were obtained : either the donor
did not regenerate and the recipient did, or, depending on the quantity
of hormone released by the donor's brain at the time of extraction, the
reverse took place. These experiments substantiated the preceding ones
perfectly : the hormone actually accumulates in the brain for the first 3
days, then from the 4th day onwards it is released into the circulation.
Hauenschild (1960) defined these phenomena even more accurately
by showing that if only half of the prostomium was removed from
H E N R I E T T E HERLANT-MEEWIS
In worms decerebrated before posterior section (Fig. 27A) no regeneration had occurred. After 30 days the worms had either healed or had
formed a pygidium again, but the lack of mitotic activity indicated no
further development. In worms decerebrated 3 days after transection
(Fig. 27B), three out of nineteen had regenerated one segment, the
others had healed or had only formed a pygidium. Clark and Bonney
concluded from their experiments that the brain plays an essential part
during the first stages of regeneration but later its presence is less
important.
For a better understanding of the brain's essential role, Clark and
Evans (1961) varied the interval between the two operations, from 30
min to 7 days. The results were the same when the two operations were
no more than 48 h apart (Fig. 28) ; the worms healed and could reconstruct a pygidium. Vascularization of the pygidium which precedes
formation of a regeneration bud, took place only when decerebration
was performed 4 days after transection. Finally, when the two operations were more than 5 days apart, regeneration occurred in a number of
cases but was considerably retarded. From these experiments, Clark
and Evans concluded that discharge of hormones into the circulation
does not begin immediately after transection ; for 3-4 days, the hormones
are stored in the brain, and if the cerebral ganglia are removed during
this period hormonal discharge cannot take place. From the 4th day
onwards, secretion of the hormonal substance begins. I t will depend on
the amount of hormone in the blood at the time of decerebration, to
what extent regeneration will be delayed or inhibited. Graft experiments have confirmed these results (Fig. 29). The brain was removed
from a worm immediately after posterior transection and was implanted
or injected as an extract into the coelomic cavity of another decerebrated worm. Neither recipient nor donor regenerated posteriorly under
those circumstances ; presumably the graft did not contain the hormones
needed for regeneration. However, if the donor's brain was removed 2-3
days after posterior transection and was then grafted in an amputated
recipient, the latter regenerated normally but the donor did not : at that
particular time the donor's brain had stored the hormone and had been
activated. Finally, if the donor's brain was taken out 4 days after
posterior transection, alternative results were obtained : either the donor
did not regenerate and the recipient did, or, depending on the quantity
of hormone released by the donor's brain at the time of extraction, the
reverse took place. These experiments substantiated the preceding ones
perfectly : the hormone actually accumulates in the brain for the first 3
days, then from the 4th day onwards it is released into the circulation.
Hauenschild (1960) defined these phenomena even more accurately
by showing that if only half of the prostomium was removed from