322
TH. LENDER
differentiation of the brain of Polycelis nigra may be inhibited by ground
brains of Dugesia lugubris or Dugesia gonocephala. The diffusion of the
inhibitory substances emitted by the brain must give rise to an anterioposterior gradient of inhibition.
These results are in agreement with the concept of the 'time-graded
regeneration field' (H. V. Brondsted, 1946, 1947, 1955, 1956; A. and
200
300
400
500
FIG. 11. Regeneration of the brain of Dugesia lugubris. Abscissa: length of the
regenerated brain. Ordinate: percentage of planarians in each category. A: crude preparation of ground heads; B : supernatant liquid from centrifuged ground heads; D : crude
preparation of ground tails; E : supernatant fluid from centrifuged ground tails; F :
controls.
H. V. Brondsted, 1952), according to which there exists in the head
blastema a point of greater regenerative power. This point would be the
site of the regeneration of the brain. It would therefore exhibit the most
advanced differentiation, accounting for the appearance of an inhibition
which prevents the regeneration of an analogous structure. According
to Török (1958), the properties of the 'time-graded regeneration field' of
Dugesia lugubris are in agreement with the structure of the nervous
system in which the number of nerve cells decreases from the front to
the rear.
The maintenance of the normal head structure of fresh-water
planarians, then, is due primarily to the emission of inhibitory substances by the brain in the course of regeneration. Other examples of
specific inhibitions of an organ by a homologous tissue are known.
Rose and Rose (1941), Tardent (1955, 1956), Steinberg (1954) showed
that the regeneration of the hydranths of Tubularia can be inhibited by
substance emitted by another hydranth. Rose (1955) also provided
evidence for specific inhibition in the embryonic development of the
organs of Rana pipiens. The brain inhibited the development of another
nervous system, the heart produced anomalies in the development of the
heart.
TH. LENDER
differentiation of the brain of Polycelis nigra may be inhibited by ground
brains of Dugesia lugubris or Dugesia gonocephala. The diffusion of the
inhibitory substances emitted by the brain must give rise to an anterioposterior gradient of inhibition.
These results are in agreement with the concept of the 'time-graded
regeneration field' (H. V. Brondsted, 1946, 1947, 1955, 1956; A. and
200
300
400
500
FIG. 11. Regeneration of the brain of Dugesia lugubris. Abscissa: length of the
regenerated brain. Ordinate: percentage of planarians in each category. A: crude preparation of ground heads; B : supernatant liquid from centrifuged ground heads; D : crude
preparation of ground tails; E : supernatant fluid from centrifuged ground tails; F :
controls.
H. V. Brondsted, 1952), according to which there exists in the head
blastema a point of greater regenerative power. This point would be the
site of the regeneration of the brain. It would therefore exhibit the most
advanced differentiation, accounting for the appearance of an inhibition
which prevents the regeneration of an analogous structure. According
to Török (1958), the properties of the 'time-graded regeneration field' of
Dugesia lugubris are in agreement with the structure of the nervous
system in which the number of nerve cells decreases from the front to
the rear.
The maintenance of the normal head structure of fresh-water
planarians, then, is due primarily to the emission of inhibitory substances by the brain in the course of regeneration. Other examples of
specific inhibitions of an organ by a homologous tissue are known.
Rose and Rose (1941), Tardent (1955, 1956), Steinberg (1954) showed
that the regeneration of the hydranths of Tubularia can be inhibited by
substance emitted by another hydranth. Rose (1955) also provided
evidence for specific inhibition in the embryonic development of the
organs of Rana pipiens. The brain inhibited the development of another
nervous system, the heart produced anomalies in the development of the
heart.