TWENTIETH CENTURY EMBRYOLOGICAL CONCEPTS
7
Silliman Lectures at Yale, which looked somewhat in the direction of the
past, and Harrison's (1945) Address at the Harvard Tercentenary, which
faced squarely into the future, were not delivered until the 1930's (in
1933 and 1936, respectively; Harrison's Silliman Lectures, delivered in
1949, have not yet appeared in print).
4
Pantin (1955) has recently set
1918 as the date for biology's breaking of tradition with its morphological
past. For embryology, the change was a gradual one, from 1869 through
to the 1930's, and it may or may not be significant that the midpoint of
the transition was passed close to the turn of the century.
It is quite often said, by those who try to outline the methods by which
science operates, that a first phase in its development consists of the
observation of data, a second, of their classification, and that there
finally follows an inquiry into their relationships. If there is any single
generalization that can be safely formulated concerning the history of
embryology as a whole, it is probably that this science has carried out
all these procedures simultaneously at all phases of its development,
from the time of Aristotle through to our own.
It can be argued, on the other hand, that embryos were first studied
as whole organisms (Aristotle, Fabricius, Harvey, Malpighi, Wolff), then
in terms of their constituent layers (Wolff, Pander, von Baer, His,
Haeckel, Spemann), next in relationship to their constituent cells (Roux,
Driesch, all the students of cell lineage, Spemann, Harrison), and finally
with reference to the components of cells, through the 19th century
largely nuclear (O. Hertwig, Boveri) though in some cases visible cytoplasmic inclusions were also investigated (Boveri, Ε. B. Wilson, Conklin). It is hardly necessary to point out that the 20th century continues
the process by describing and analyzing both the visible and invisible
nuclear and cytoplasmic elements of the cell in terms of their constituent
molecules.
The integrative powers of the embryo, at all of its levels, are however
so pervasive that they never permit themselves to be overlooked by
those who avail themselves of the privilege of looking at the embryo at
all. The result has been that when each of the practices just enumerated
became fashionable, the previous one was never completely outmoded;
and when, at each stage of its development, embryology has added a new
dimension to its studies, it has never wholly discarded the old ones. Spe4
Harrison's Silliman Lectures were entitled "Organization and Development of
the Embryo." The titles of the six individual lectures were: Introduction; The
Egg and Early Stages of Development; Autonomy and Mutual Dependence of Cells;
The Nervous System; The Symmetry of Organisms; and Development and Growth
in Complex Systems.
7
Silliman Lectures at Yale, which looked somewhat in the direction of the
past, and Harrison's (1945) Address at the Harvard Tercentenary, which
faced squarely into the future, were not delivered until the 1930's (in
1933 and 1936, respectively; Harrison's Silliman Lectures, delivered in
1949, have not yet appeared in print).
4
Pantin (1955) has recently set
1918 as the date for biology's breaking of tradition with its morphological
past. For embryology, the change was a gradual one, from 1869 through
to the 1930's, and it may or may not be significant that the midpoint of
the transition was passed close to the turn of the century.
It is quite often said, by those who try to outline the methods by which
science operates, that a first phase in its development consists of the
observation of data, a second, of their classification, and that there
finally follows an inquiry into their relationships. If there is any single
generalization that can be safely formulated concerning the history of
embryology as a whole, it is probably that this science has carried out
all these procedures simultaneously at all phases of its development,
from the time of Aristotle through to our own.
It can be argued, on the other hand, that embryos were first studied
as whole organisms (Aristotle, Fabricius, Harvey, Malpighi, Wolff), then
in terms of their constituent layers (Wolff, Pander, von Baer, His,
Haeckel, Spemann), next in relationship to their constituent cells (Roux,
Driesch, all the students of cell lineage, Spemann, Harrison), and finally
with reference to the components of cells, through the 19th century
largely nuclear (O. Hertwig, Boveri) though in some cases visible cytoplasmic inclusions were also investigated (Boveri, Ε. B. Wilson, Conklin). It is hardly necessary to point out that the 20th century continues
the process by describing and analyzing both the visible and invisible
nuclear and cytoplasmic elements of the cell in terms of their constituent
molecules.
The integrative powers of the embryo, at all of its levels, are however
so pervasive that they never permit themselves to be overlooked by
those who avail themselves of the privilege of looking at the embryo at
all. The result has been that when each of the practices just enumerated
became fashionable, the previous one was never completely outmoded;
and when, at each stage of its development, embryology has added a new
dimension to its studies, it has never wholly discarded the old ones. Spe4
Harrison's Silliman Lectures were entitled "Organization and Development of
the Embryo." The titles of the six individual lectures were: Introduction; The
Egg and Early Stages of Development; Autonomy and Mutual Dependence of Cells;
The Nervous System; The Symmetry of Organisms; and Development and Growth
in Complex Systems.