18
JANE Μ. OPPENHEIMER
III. THE EMBRYO AS CONSTRUCTED OF GERM LAYERS
If too much significance may seem to have been attributed in the
preceding section to the concept of the axial gradient, nevertheless such
emphasis can be defended by the insistence that this concept has been
one of the funnels through which the 19th century has poured its ideas
into the 20th. Another concept which to some extent has filled a like
function is the germ layer doctrine, which during the 19th century not
only interpreted the layers as primary entities in the developing organism, but went so far as to raise their specificity of origin and action to
the level of a formal generalizing principle for embryology (witness, for
instance, the statement in Ziegler's textbook in 1902, cited from Mangold,
1923, p. 272):
. . Wenn bei den Wirbeltieren die Gastrulation beendet ist und
die Keimblätter gebildet sind, so haben diese Keimblätter ganz
getrennte Aufgaben in bezug auf ihre Beteiligung an den Organen
und die Bildung der Gewebe. Dieser Satz spricht die Lehre von der
Spezifizität der Keimblätter aus, welche eines der wichtigsten
allgemeinen Resultate der embryologischen Forschung ist."
9
To formulate a romantic analogy, the 19th century might have intimated
that the germ layers are the phrases in which the embryo composes its
melodies.
The development of the germ layer concept through to the beginning
of the 20th century has been presented in another place (Oppenheimer,
1940). Suffice it to state here that by the end of the 19th century an
unquestioning belief in the specificity of the layers was so widely, although not universally maintained (see Mangold, 1923, and Oppenheimer, 1940, for discussion of some 19th century doubts concerning the
dogmatic value of the principle), that on a conceptual plane one of the
more progressive contributions of the early part of the 20th century was
the demonstration by operative techniques of the modifiability of the
layers in a number of organisms; in the amphibians, for instance, first as
an extension of the investigations on the organizer (Mangold, 1923);
and later in the echinoderms (von Ubisch, 1925, Hörstadius, 1928) as related to polar gradients. (It had in fact already in the previous century
been demonstrated for the echinoderms by Herbst, 1892, 1893 by chemi9
When gastrulation is completed in the vertebrates and the germ layers are
formed, these layers have quite separate tasks with regard to their participation in
organs and the construction of tissues. This proposition expresses the doctrine of the
specificity of the germ layers, which is one of the most important general results
of embryological research.
JANE Μ. OPPENHEIMER
III. THE EMBRYO AS CONSTRUCTED OF GERM LAYERS
If too much significance may seem to have been attributed in the
preceding section to the concept of the axial gradient, nevertheless such
emphasis can be defended by the insistence that this concept has been
one of the funnels through which the 19th century has poured its ideas
into the 20th. Another concept which to some extent has filled a like
function is the germ layer doctrine, which during the 19th century not
only interpreted the layers as primary entities in the developing organism, but went so far as to raise their specificity of origin and action to
the level of a formal generalizing principle for embryology (witness, for
instance, the statement in Ziegler's textbook in 1902, cited from Mangold,
1923, p. 272):
. . Wenn bei den Wirbeltieren die Gastrulation beendet ist und
die Keimblätter gebildet sind, so haben diese Keimblätter ganz
getrennte Aufgaben in bezug auf ihre Beteiligung an den Organen
und die Bildung der Gewebe. Dieser Satz spricht die Lehre von der
Spezifizität der Keimblätter aus, welche eines der wichtigsten
allgemeinen Resultate der embryologischen Forschung ist."
9
To formulate a romantic analogy, the 19th century might have intimated
that the germ layers are the phrases in which the embryo composes its
melodies.
The development of the germ layer concept through to the beginning
of the 20th century has been presented in another place (Oppenheimer,
1940). Suffice it to state here that by the end of the 19th century an
unquestioning belief in the specificity of the layers was so widely, although not universally maintained (see Mangold, 1923, and Oppenheimer, 1940, for discussion of some 19th century doubts concerning the
dogmatic value of the principle), that on a conceptual plane one of the
more progressive contributions of the early part of the 20th century was
the demonstration by operative techniques of the modifiability of the
layers in a number of organisms; in the amphibians, for instance, first as
an extension of the investigations on the organizer (Mangold, 1923);
and later in the echinoderms (von Ubisch, 1925, Hörstadius, 1928) as related to polar gradients. (It had in fact already in the previous century
been demonstrated for the echinoderms by Herbst, 1892, 1893 by chemi9
When gastrulation is completed in the vertebrates and the germ layers are
formed, these layers have quite separate tasks with regard to their participation in
organs and the construction of tissues. This proposition expresses the doctrine of the
specificity of the germ layers, which is one of the most important general results
of embryological research.