CELL DIVISIONS
349
under the influence of Li ions (Agrell, 1956) (cf. IV, D, 2) is accompanied
by a delay in differentiation and by vegetalization. The vegetalizing
action of Li ions was interpreted by Agrell as due to the decreased
differentiation (
£ embryonalizing action').
C. Effect of Temporary Isolation of the Embryonic Material
in Physiological Solution
A correlation between the morphogenetic properties of embryonic
rudiments and the age of their component cells is also demonstrated by
the change in competence of the ectoderm of the early gastrula after its
cultivation in saline solution for different lengths of times (Holtfreter,
1938a; Gallera, 1952). When transplanted into inducing regions of
the newt or Bombina neurula the explanted ectoderm of Triton
alpestris
develops different structures depending on the duration of its stay in the
saline. With the prolongation of this time the morphogenetic abilities of
the ectoderm diminish both qualitatively and quantitatively; these
changes proceeding mainly in parallel with the changes in the morphogenetic properties of the ectoderm of the intact control embryo.
Holtfreter writes 'Die Reaktionsänderung im Ektoderm ist ein zeitgebundener, autonomer Vorgang' (1938a). In other words, the character
of the morphogenetic responses changes concurrently with the changes
in cell generation and the sum total duration of the interkinetic states of
the ectodermal cells.
Latent regional differentiation of the entoderm may serve as another
example of a correlation between the morphogenetic properties of
embryonic rudiments and the age of their cells. Regional isolation of the
entoderm in Triturus pyrrhogaster
(Okada, 1957, 1960a, b; Takata,
1960a, b) takes place during the period from the neurula stage to the tail
bud stage; this process is accelerated and partly regionalized by
mesodermal rudiments adjacent to the entoderm: ento- and ectomesenchyme displace differentiation towards the formation of pharynx,
while mesothelium displaces it towards the formation of intestine.
The experiments of Okada (1960a) showed, however, that regionalization of the entoderm can proceed without the participation of the
mesoderm, so that it is an 'autonomous process'. Okada took pluripotent
future branchial material from an early neurula and explanted it in
Holtfreter's solution, for 24 or 48 hours, after which it was associated
with the ventral portion of the lateral mesoderm, that is with the
rudiment of the mesothelium. The expiants kept in the salt solution for
24 hours when connected with the lateral mesoderm formed intestinal
and oesophago-gastric structures, thus showing pluripotency, while
those kept for 48 hours developed more pharynx and pharyngoid
structures. Thus the process of autonomous regionalization and a
349
under the influence of Li ions (Agrell, 1956) (cf. IV, D, 2) is accompanied
by a delay in differentiation and by vegetalization. The vegetalizing
action of Li ions was interpreted by Agrell as due to the decreased
differentiation (
£ embryonalizing action').
C. Effect of Temporary Isolation of the Embryonic Material
in Physiological Solution
A correlation between the morphogenetic properties of embryonic
rudiments and the age of their component cells is also demonstrated by
the change in competence of the ectoderm of the early gastrula after its
cultivation in saline solution for different lengths of times (Holtfreter,
1938a; Gallera, 1952). When transplanted into inducing regions of
the newt or Bombina neurula the explanted ectoderm of Triton
alpestris
develops different structures depending on the duration of its stay in the
saline. With the prolongation of this time the morphogenetic abilities of
the ectoderm diminish both qualitatively and quantitatively; these
changes proceeding mainly in parallel with the changes in the morphogenetic properties of the ectoderm of the intact control embryo.
Holtfreter writes 'Die Reaktionsänderung im Ektoderm ist ein zeitgebundener, autonomer Vorgang' (1938a). In other words, the character
of the morphogenetic responses changes concurrently with the changes
in cell generation and the sum total duration of the interkinetic states of
the ectodermal cells.
Latent regional differentiation of the entoderm may serve as another
example of a correlation between the morphogenetic properties of
embryonic rudiments and the age of their cells. Regional isolation of the
entoderm in Triturus pyrrhogaster
(Okada, 1957, 1960a, b; Takata,
1960a, b) takes place during the period from the neurula stage to the tail
bud stage; this process is accelerated and partly regionalized by
mesodermal rudiments adjacent to the entoderm: ento- and ectomesenchyme displace differentiation towards the formation of pharynx,
while mesothelium displaces it towards the formation of intestine.
The experiments of Okada (1960a) showed, however, that regionalization of the entoderm can proceed without the participation of the
mesoderm, so that it is an 'autonomous process'. Okada took pluripotent
future branchial material from an early neurula and explanted it in
Holtfreter's solution, for 24 or 48 hours, after which it was associated
with the ventral portion of the lateral mesoderm, that is with the
rudiment of the mesothelium. The expiants kept in the salt solution for
24 hours when connected with the lateral mesoderm formed intestinal
and oesophago-gastric structures, thus showing pluripotency, while
those kept for 48 hours developed more pharynx and pharyngoid
structures. Thus the process of autonomous regionalization and a