TWENTIETH CENTURY EMBRYOLOGICAL CONCEPTS
9
vertebrate axis produces its diversity as a result of quantitative variation
in the distribution of a single substance. The axial gradient concept,
from its birth to its demise, never deviated from its conviction that axial
differences in an organism are to be explained exclusively on a quantitative basis.
The patrons of these concepts were well aware of the discrepancies
between their rival interpretations, and were in fact rather strongly
critical of each other, Spemann (1938, Chapter XVI) somewhat philosophically, Child (1946) in fairly tart polemics. Yet though both workers
might have hesitated to admit it, their concepts shared in many respects
both heritage and effect, and some of their common features may well
be considered as illustrative of the mode in which these theories of the
beginning third of the century intermediated between the concepts of the
19th century and the problems that are being experimentally investigated
today.
The concepts both of Spemann and Child stemmed ultimately from
the same roots in the concept of polarity. It is astonishing that the early
history of ideas concerning polarity has never been comprehensively
treated for the animal egg (see Harrison, 1945, for a brief summary and
some key references). Unfortunately the background for this concept is
too broad to be adequately covered here. The nature of polarity was
an enigma which fascinated the romantic biologists of the 18th and 19th
centuries, and polar differentiation seems first to have been discussed
with respect to the animal egg by von Baer, who was himself often
strongly influenced by romanticism. Driesch too was vastly concerned
with polarity, and he considered it, almost certainly under the influence
of electromagnetic field theory, first in terms of the orientation of the
blastomeres themselves ["Man denke sich jede Blastomere als Magneten
oder auch mit zweifacher Elektrizität geladen, so hat man ein Bild der
Sache"
5
(Driesch, 1894, p. 22)], finally in terms of a directed polar
orientation of the smallest components of the plasma ["Den Richtungsbau
hat man als blosse Polarität, meinetwegen im Bilde als elektrische
Polarität der kleinsten Teile, zu denken/'
6
(Driesch, 1894, p. 100)].
Boveri, always one of the profoundest of his contemporaries in embryological wisdom, went beyond Driesch; while he also referred the polar
qualities of the egg to the properties of its minute constituents, he drew
attention to a visible stratification of demonstrable elements in the egg
5
One might think of each blastomere as a magnet or as provided with opposite
electrical charges, then one would have a picture of the state of affairs.
6
One has to consider orientation-structure as plain polarity, in my opinion as an
image of electrical polarity of the smallest parts.
9
vertebrate axis produces its diversity as a result of quantitative variation
in the distribution of a single substance. The axial gradient concept,
from its birth to its demise, never deviated from its conviction that axial
differences in an organism are to be explained exclusively on a quantitative basis.
The patrons of these concepts were well aware of the discrepancies
between their rival interpretations, and were in fact rather strongly
critical of each other, Spemann (1938, Chapter XVI) somewhat philosophically, Child (1946) in fairly tart polemics. Yet though both workers
might have hesitated to admit it, their concepts shared in many respects
both heritage and effect, and some of their common features may well
be considered as illustrative of the mode in which these theories of the
beginning third of the century intermediated between the concepts of the
19th century and the problems that are being experimentally investigated
today.
The concepts both of Spemann and Child stemmed ultimately from
the same roots in the concept of polarity. It is astonishing that the early
history of ideas concerning polarity has never been comprehensively
treated for the animal egg (see Harrison, 1945, for a brief summary and
some key references). Unfortunately the background for this concept is
too broad to be adequately covered here. The nature of polarity was
an enigma which fascinated the romantic biologists of the 18th and 19th
centuries, and polar differentiation seems first to have been discussed
with respect to the animal egg by von Baer, who was himself often
strongly influenced by romanticism. Driesch too was vastly concerned
with polarity, and he considered it, almost certainly under the influence
of electromagnetic field theory, first in terms of the orientation of the
blastomeres themselves ["Man denke sich jede Blastomere als Magneten
oder auch mit zweifacher Elektrizität geladen, so hat man ein Bild der
Sache"
5
(Driesch, 1894, p. 22)], finally in terms of a directed polar
orientation of the smallest components of the plasma ["Den Richtungsbau
hat man als blosse Polarität, meinetwegen im Bilde als elektrische
Polarität der kleinsten Teile, zu denken/'
6
(Driesch, 1894, p. 100)].
Boveri, always one of the profoundest of his contemporaries in embryological wisdom, went beyond Driesch; while he also referred the polar
qualities of the egg to the properties of its minute constituents, he drew
attention to a visible stratification of demonstrable elements in the egg
5
One might think of each blastomere as a magnet or as provided with opposite
electrical charges, then one would have a picture of the state of affairs.
6
One has to consider orientation-structure as plain polarity, in my opinion as an
image of electrical polarity of the smallest parts.