TWENTIETH CENTURY EMBRYOLOGICAL CONCEPTS
27
problems which relate to specificity are the central target of all biological investigations. In embryology in the 19th century the fixity of the
germ layers was defined by the very word specificity.
Roux used the
word Specification
as we do the word differentiation [see his article
Ueber die Spezifikation der Furchungszellen und über die bei der Postgeneration und Regeneration anzunehmenden Vorgänge,
13 1893; or his
definition of Specification
in his "Terminologie," 1912, p. 385, as "die
Entstehung, Bildung der Specietät, der Eigenart. Sie kann betreffen die
Potenz . . . oder die entwickelte Beschaffenheit, die Differenzierung"
14
].
Thus in his meaning of the word all research directed toward the study
of differentiation is concerned also with specificity.
More particularly, however, 20th century biology analyzes specificity,
developmental or otherwise, with reference to the concepts of two special
areas of thought, one of them genetics, and the other, the so-called
molecular biology. Ideally these two methods approach each other very
closely; even at a realistic level they share in common the fact that they
consider cells in terms of agents functioning at the subcellular level.
They deal with cellular inclusions, visible or otherwise, as primary factors, and it is a feature of the 20th century, as opposed to the 19th, that
investigations of cellular inclusions of microscopically visible dimensions
can no longer be considered apart from those treating of systems of
molecular size or nature. The mid-20th century's interest in Gustafson's
correlation of gradients with mitochondrial distribution is measured by
its reference of mitochondria to their metabolic action.
To take up first genetics: The practice of considering hereditary factors
in relation to morphogenetic factors is very ancient. In the period to
which this essay limits itself, attempts to verify or refute an embryological theory based by Roux on Weismann's concept of the qualitative distribution of the chromosomes are commonly recognized as having been
highly influential by providing a vigorous impetus for the new experimental investigations of development at the turn of the century. Boveri's
study (1907) on the development of dispermic echinoderm eggs demonstrating the existence of qualitative differences between the chromosomes, and more important, the importance to normal development of
their equable distribution to all cells was worked out with the utmost
ingenuity on strictly embryological material, without recourse to the type
of knowledge of hereditary factors that was contemporaneously be13
On the Specification of the Cleavage Cells and on the Processes Presumed to
Occur in Postgeneration and Regeneration.
14
The origin, the production of speciety, of specialty. It can concern poteniality ... or developed characteristics, differentiation.
27
problems which relate to specificity are the central target of all biological investigations. In embryology in the 19th century the fixity of the
germ layers was defined by the very word specificity.
Roux used the
word Specification
as we do the word differentiation [see his article
Ueber die Spezifikation der Furchungszellen und über die bei der Postgeneration und Regeneration anzunehmenden Vorgänge,
13 1893; or his
definition of Specification
in his "Terminologie," 1912, p. 385, as "die
Entstehung, Bildung der Specietät, der Eigenart. Sie kann betreffen die
Potenz . . . oder die entwickelte Beschaffenheit, die Differenzierung"
14
].
Thus in his meaning of the word all research directed toward the study
of differentiation is concerned also with specificity.
More particularly, however, 20th century biology analyzes specificity,
developmental or otherwise, with reference to the concepts of two special
areas of thought, one of them genetics, and the other, the so-called
molecular biology. Ideally these two methods approach each other very
closely; even at a realistic level they share in common the fact that they
consider cells in terms of agents functioning at the subcellular level.
They deal with cellular inclusions, visible or otherwise, as primary factors, and it is a feature of the 20th century, as opposed to the 19th, that
investigations of cellular inclusions of microscopically visible dimensions
can no longer be considered apart from those treating of systems of
molecular size or nature. The mid-20th century's interest in Gustafson's
correlation of gradients with mitochondrial distribution is measured by
its reference of mitochondria to their metabolic action.
To take up first genetics: The practice of considering hereditary factors
in relation to morphogenetic factors is very ancient. In the period to
which this essay limits itself, attempts to verify or refute an embryological theory based by Roux on Weismann's concept of the qualitative distribution of the chromosomes are commonly recognized as having been
highly influential by providing a vigorous impetus for the new experimental investigations of development at the turn of the century. Boveri's
study (1907) on the development of dispermic echinoderm eggs demonstrating the existence of qualitative differences between the chromosomes, and more important, the importance to normal development of
their equable distribution to all cells was worked out with the utmost
ingenuity on strictly embryological material, without recourse to the type
of knowledge of hereditary factors that was contemporaneously be13
On the Specification of the Cleavage Cells and on the Processes Presumed to
Occur in Postgeneration and Regeneration.
14
The origin, the production of speciety, of specialty. It can concern poteniality ... or developed characteristics, differentiation.