M O R P H O G E N E S I S OF F R E S H - W A T E R P L A N A R I A
329
accumulation of neoblasts. Wolff (1953) showed how the different
phases which follow in sequence during the regeneration of an anterior
region, are probably linked together. This still valid scheme can be
completed by taking into account recent findings (Fig. 14).
Towards the second or third day after the isolation of a caudal region,
the first nerve cells differentiate in the anterior blastema. The brain is
built up in the most active zone of the so-called 'time-graded regeneration field' (Brondsted, 1946 et seq.). It liberates inhibitory substances
which prevent regeneration of another brain. The cephalic region during
differentiation induces a prepharyngeal region which causes the
appearance of a pharyngeal region. The latter has the ability to regenerate a pharynx. At the same time, the 'organisines', secreted by the
brain, induce the differentiation of the eyes. Gonads which regenerate
may be induced by testes present in the old tissues. These successive
inductions take place at certain levels by means of chemical substances.
This scheme does not bring into play the theory of physiological
gradients as the basis for an explanation of regeneration. The axial
gradients of Child (1928) are not the cause of the harmonious unfolding
of regeneration but rather the consequence of the dominance of the brain
over the rest of the body. They are superimposed on the diffusion
gradient of inhibitory or inductive substances.
A new step toward the understanding of the phenomena of regeneration will be possible when selective manipulation of the different
reactions which take place during organ differentiation can be accomplished.
References
Abeloos, M. (1930). Bull. biol. 64, 1.
Abeloos, M. (1932). ' L a regeneration et les problemes de la morphogenese'. 253 p p .
Gauthier-Villars, Paris.
Bondi, C. (1958a). Riv. Biol. 50, 91.
Bondi, C. (1958b). Ada Embryol. 2, 94.
Bondi, C. (1959). Arch. zool. (ital), Napoli 44, 141.
Brondsted, A. a n d Brondsted, H . V. (1952). Vidensk. Medd. dansk. naturh. Foren.
Kbh. 114, 443.
Brondsted, H . V. (1939). Biol. Medd., Kbh. 15, 1.
Brondsted, H . V. (1942). Vidensk. Medd. dansk. naturh. Foren. Kbh. 106, 253.
Brondsted, H . V. (1946). Biol. Medd., Kbh. 20, 1.
Brondsted, H . V. (1947). Vlth Int. Congr. Cell Biol., 585.
B r o n d s t e d , H . V. (1955). Biol. Rev. 30, 65.
B r o n d s t e d , H . V. (1956). Biol. Medd., Kbh. 23, 1.
Chandebois, R . (1957). C. R. Acad. Sei., Paris 245, 1177.
Chandebois, R. (1960a). Bull. Soc. zool. Fr. 84, 434.
329
accumulation of neoblasts. Wolff (1953) showed how the different
phases which follow in sequence during the regeneration of an anterior
region, are probably linked together. This still valid scheme can be
completed by taking into account recent findings (Fig. 14).
Towards the second or third day after the isolation of a caudal region,
the first nerve cells differentiate in the anterior blastema. The brain is
built up in the most active zone of the so-called 'time-graded regeneration field' (Brondsted, 1946 et seq.). It liberates inhibitory substances
which prevent regeneration of another brain. The cephalic region during
differentiation induces a prepharyngeal region which causes the
appearance of a pharyngeal region. The latter has the ability to regenerate a pharynx. At the same time, the 'organisines', secreted by the
brain, induce the differentiation of the eyes. Gonads which regenerate
may be induced by testes present in the old tissues. These successive
inductions take place at certain levels by means of chemical substances.
This scheme does not bring into play the theory of physiological
gradients as the basis for an explanation of regeneration. The axial
gradients of Child (1928) are not the cause of the harmonious unfolding
of regeneration but rather the consequence of the dominance of the brain
over the rest of the body. They are superimposed on the diffusion
gradient of inhibitory or inductive substances.
A new step toward the understanding of the phenomena of regeneration will be possible when selective manipulation of the different
reactions which take place during organ differentiation can be accomplished.
References
Abeloos, M. (1930). Bull. biol. 64, 1.
Abeloos, M. (1932). ' L a regeneration et les problemes de la morphogenese'. 253 p p .
Gauthier-Villars, Paris.
Bondi, C. (1958a). Riv. Biol. 50, 91.
Bondi, C. (1958b). Ada Embryol. 2, 94.
Bondi, C. (1959). Arch. zool. (ital), Napoli 44, 141.
Brondsted, A. a n d Brondsted, H . V. (1952). Vidensk. Medd. dansk. naturh. Foren.
Kbh. 114, 443.
Brondsted, H . V. (1939). Biol. Medd., Kbh. 15, 1.
Brondsted, H . V. (1942). Vidensk. Medd. dansk. naturh. Foren. Kbh. 106, 253.
Brondsted, H . V. (1946). Biol. Medd., Kbh. 20, 1.
Brondsted, H . V. (1947). Vlth Int. Congr. Cell Biol., 585.
B r o n d s t e d , H . V. (1955). Biol. Rev. 30, 65.
B r o n d s t e d , H . V. (1956). Biol. Medd., Kbh. 23, 1.
Chandebois, R . (1957). C. R. Acad. Sei., Paris 245, 1177.
Chandebois, R. (1960a). Bull. Soc. zool. Fr. 84, 434.