8
JANE Μ. OPPENHEIMER
mann, for instance, who analyzed the relations between layers in terms
of cellular interactions, never lost sight of the whole embryo. These
effects have, as a matter of clear cold fact, been cumulative throughout
the centuries, with the result that even in the 20th century the embryo
is still being actively investigated at all of its levels: as a whole, in terms
of its layers, of its cells, and of their microscopic and submicroscopic constituents. Selected aspects of studies carried out at all of these levels
will be taken up briefly in the main text to follow.
II. THE WHOLE EMBRYO
While the contributions of Roux and Driesch possess too many virtues
for individual commendation, it may be pointed out here that one of the
principal merits of both investigators was that when they considered the
action of a particular part of the embryo, they both referred that action,
different though this was construed to be according to the interpretation
of each, to the whole embryo. The fact that both of them remembered
the embryo in its entirety remained eminently influential on subsequent
workers during the first two or three decades of the 20th century; and
it was in terms of the whole embryo that the two principal overt attempts
of the early part of the century towards the formulation of generalizing
concepts were expressed. I refer to the concepts of the axial gradient, as
developed by Child and his adherents; and of the organizer, as developed by Spemann and his followers (see Bautzmann, 1955, for an
extended statement of the history and the present status of the organizer
concept).
These two concepts were in many ways, as expressed by their originators, highly disparate. The organizer concept was designed as an interpretation of phenomena peculiar to rather specific stages of embryonic
development; the axial gradient concept, which originally grew out of
studies of regeneration, was extended later to cover phenomena characteristic of many phases not only of morphogenesis but of the whole
life cycle. The organizer concept, though transcending in implication
the limits of any particular taxonomic category, was developed almost
exclusively as a result of experimentation on a specific group, the vertebrates; the data adduced in support of the axial gradient concept were
drawn from observations on a far greater range of biological forms. The
organizer concept, at least as developed by Spemann, tended on the
whole to account for regional differences, at least within the medullary
plate, on a qualitative basis, though to be sure some later devotees of
the organizer concept, for whom Dalcq (Dalcq and Pasteéis, 1937) might
be considered as spokesman, modified this view to consider that the
JANE Μ. OPPENHEIMER
mann, for instance, who analyzed the relations between layers in terms
of cellular interactions, never lost sight of the whole embryo. These
effects have, as a matter of clear cold fact, been cumulative throughout
the centuries, with the result that even in the 20th century the embryo
is still being actively investigated at all of its levels: as a whole, in terms
of its layers, of its cells, and of their microscopic and submicroscopic constituents. Selected aspects of studies carried out at all of these levels
will be taken up briefly in the main text to follow.
II. THE WHOLE EMBRYO
While the contributions of Roux and Driesch possess too many virtues
for individual commendation, it may be pointed out here that one of the
principal merits of both investigators was that when they considered the
action of a particular part of the embryo, they both referred that action,
different though this was construed to be according to the interpretation
of each, to the whole embryo. The fact that both of them remembered
the embryo in its entirety remained eminently influential on subsequent
workers during the first two or three decades of the 20th century; and
it was in terms of the whole embryo that the two principal overt attempts
of the early part of the century towards the formulation of generalizing
concepts were expressed. I refer to the concepts of the axial gradient, as
developed by Child and his adherents; and of the organizer, as developed by Spemann and his followers (see Bautzmann, 1955, for an
extended statement of the history and the present status of the organizer
concept).
These two concepts were in many ways, as expressed by their originators, highly disparate. The organizer concept was designed as an interpretation of phenomena peculiar to rather specific stages of embryonic
development; the axial gradient concept, which originally grew out of
studies of regeneration, was extended later to cover phenomena characteristic of many phases not only of morphogenesis but of the whole
life cycle. The organizer concept, though transcending in implication
the limits of any particular taxonomic category, was developed almost
exclusively as a result of experimentation on a specific group, the vertebrates; the data adduced in support of the axial gradient concept were
drawn from observations on a far greater range of biological forms. The
organizer concept, at least as developed by Spemann, tended on the
whole to account for regional differences, at least within the medullary
plate, on a qualitative basis, though to be sure some later devotees of
the organizer concept, for whom Dalcq (Dalcq and Pasteéis, 1937) might
be considered as spokesman, modified this view to consider that the