15. E M B R Y O G E N E S I S in vitro
541
situated in the vicinity of the blastoporal lip of the young gastrula
(Fig. 6), and the trunk inducer is supplied by the posterior archenteric
roof of the neurula. The experimental results have settled once and for
all the old controversy of the regional differentiation of the embryo.
It does not depend on the regional nature of the ectoderm, but on the
nature of the inducer. The cephalic inducer provokes differentiation
of cerebral vesicles, eyes, crystalline lenses, olfactory organs, otocysts,
teeth, tentacles, and numerous other cephalic structures. The truncocaudal inducer provokes morphogenesis of a well-formed tail, recognizable by its external shape, and equipped with fins, covered with
pigment, and containing spinal cord, notochord, muscles, and a terminal part of the intestine with an anus. (This last point was confirmed
recently by Takata and Yamada, 1960.)
Further, these investigations show, amongst many other results, that
a lateral half of the inducer is capable of provoking the differentiation
of symmetrically bilateral structures, which confirms its self-regulatory
power. Moreover, a living inducer retains its properties for several
days after having been explanted.
2. Action of Killed Inducing and Non-inducing Tissues of the Urodele Embryo
The next problem that presented itself was to know whether the
chordo-mesodermal area can act only in the living state, or whether
it keeps its properties after having been killed by physical or chemical
means. In 1932, a joint report by Bautzmann, Holtfreter, Spemann and
Mangold, established that a blastoporal lip, killed by various means
(heat, desiccation, freezing, alcohol), retains its capacity to induce a
neural plate in an undifferentiated ectoderm. Similarly, a piece of
agar, placed in contact with a live inducer, acquired this propertyAccording to the work of Holtfreter (1934), inducing power resists
treatment by damp heat (60-100°C) for lh, resists desiccation at
high temperatures (100-150°C), and can withstand prolonged treatment with alcohol, xylol and paraffin, since pieces of tissue fixed and
imbedded for histological investigation do not lose their efficacy.
Similarly, the blastoporal lip, irradiated by X-rays, keeps its organizing
power (Wolff and Reyss-Brion, 1957) (Fig. 7).
Furthermore, certain tissues of the gastrula or of the embryo, which
are non-inducers in their living state, acquired this property after
death. This was found to be true with regard to the ectoderm and the
endoderm of the young gastrula, the yolk plates of the undivided egg,
the supernatant fluid from crushed ovarian eggs of Triton, centrifuged
after coagulation by heat. Nevertheless, treatments by various destructive agents, if they do not abolish the inducing power, may change
the quality of the differentiation produced. Mesodermal differentiations
541
situated in the vicinity of the blastoporal lip of the young gastrula
(Fig. 6), and the trunk inducer is supplied by the posterior archenteric
roof of the neurula. The experimental results have settled once and for
all the old controversy of the regional differentiation of the embryo.
It does not depend on the regional nature of the ectoderm, but on the
nature of the inducer. The cephalic inducer provokes differentiation
of cerebral vesicles, eyes, crystalline lenses, olfactory organs, otocysts,
teeth, tentacles, and numerous other cephalic structures. The truncocaudal inducer provokes morphogenesis of a well-formed tail, recognizable by its external shape, and equipped with fins, covered with
pigment, and containing spinal cord, notochord, muscles, and a terminal part of the intestine with an anus. (This last point was confirmed
recently by Takata and Yamada, 1960.)
Further, these investigations show, amongst many other results, that
a lateral half of the inducer is capable of provoking the differentiation
of symmetrically bilateral structures, which confirms its self-regulatory
power. Moreover, a living inducer retains its properties for several
days after having been explanted.
2. Action of Killed Inducing and Non-inducing Tissues of the Urodele Embryo
The next problem that presented itself was to know whether the
chordo-mesodermal area can act only in the living state, or whether
it keeps its properties after having been killed by physical or chemical
means. In 1932, a joint report by Bautzmann, Holtfreter, Spemann and
Mangold, established that a blastoporal lip, killed by various means
(heat, desiccation, freezing, alcohol), retains its capacity to induce a
neural plate in an undifferentiated ectoderm. Similarly, a piece of
agar, placed in contact with a live inducer, acquired this propertyAccording to the work of Holtfreter (1934), inducing power resists
treatment by damp heat (60-100°C) for lh, resists desiccation at
high temperatures (100-150°C), and can withstand prolonged treatment with alcohol, xylol and paraffin, since pieces of tissue fixed and
imbedded for histological investigation do not lose their efficacy.
Similarly, the blastoporal lip, irradiated by X-rays, keeps its organizing
power (Wolff and Reyss-Brion, 1957) (Fig. 7).
Furthermore, certain tissues of the gastrula or of the embryo, which
are non-inducers in their living state, acquired this property after
death. This was found to be true with regard to the ectoderm and the
endoderm of the young gastrula, the yolk plates of the undivided egg,
the supernatant fluid from crushed ovarian eggs of Triton, centrifuged
after coagulation by heat. Nevertheless, treatments by various destructive agents, if they do not abolish the inducing power, may change
the quality of the differentiation produced. Mesodermal differentiations