TWENTIETH CENTURY EMBRYOLOGICAL CONCEPTS
23
importance of the amphibian surface coat in cellular movements has
proved to be a descriptive contribution of the first order of significance.
It places a new emphasis on a supercellular entity governing the movements of the cells, which now supplants the germ layer as the next higher
order of integration above the individual cell. While the 20th century
has as yet formulated no new specific generalizing concept in cellular
terms to supplant the germ layer theory, it has through this simple and
original contribution of Holtfreter turned the investigation of morphogenesis to an entirely different direction than has been followed for many
years.
IV. THE EMBRYO AS CONSTRUCTED OF CELLS
1.
THE WHOLE CELL
The developmental significance of Holtfreter's surface coat is of course
primarily that this is an agent which organizes the movements of cells.
To further embellish our earlier metaphor, if the germ layers, designated
as such by the 19th century, represent the phrases of the embryo's tunes,
the cells represent the notes. "The reference of developmental processes
to the cell," wrote Harrison in 1937 (p. 372), "was the most important
step ever taken in embryology," and it seems unlikely that he is soon
to be contradicted.
In the same way as the embryology of the 20th century has retained
yet altered the 19th century concept of germ layers, so does it still bear
the clear marks of influence, however modified these may have become,
of the 19th century cell doctrine; to confirm this point, one has only
to regard the titles of many of the periodicals in which embryological
articles are now being published: The Journal of Cellular and Comparative Physiology; Experimental Cell Research; The Proceedings of the
Congresses of Cell Biology; and so forth. In fact, while our views of the
cell theory itself have, as other historians have pointed out (J. W. Wilson,
1944, 1947a, b; Baker, 1948, 1949, 1952, 1953, 1955), undergone a
process of gradual change, it may well be mainly by virtue of the
heritage of 19th century dogma that the word cell is such a frequent
biological term; yet much of what is being discussed by so-called cell
biologists impinges less on cells qua cells than on their mere constituents,
whether membranes and inclusions on the morphological side, or enzyme
systems on the functional. Indeed, some of the work on homogenates is
so far from cellular that it might more befittingly be called uncellular
biology or uncellular physiology.
But if the division of biology which today encompasses much of embryology is called cell biology, this results only partly from the proverbial
23
importance of the amphibian surface coat in cellular movements has
proved to be a descriptive contribution of the first order of significance.
It places a new emphasis on a supercellular entity governing the movements of the cells, which now supplants the germ layer as the next higher
order of integration above the individual cell. While the 20th century
has as yet formulated no new specific generalizing concept in cellular
terms to supplant the germ layer theory, it has through this simple and
original contribution of Holtfreter turned the investigation of morphogenesis to an entirely different direction than has been followed for many
years.
IV. THE EMBRYO AS CONSTRUCTED OF CELLS
1.
THE WHOLE CELL
The developmental significance of Holtfreter's surface coat is of course
primarily that this is an agent which organizes the movements of cells.
To further embellish our earlier metaphor, if the germ layers, designated
as such by the 19th century, represent the phrases of the embryo's tunes,
the cells represent the notes. "The reference of developmental processes
to the cell," wrote Harrison in 1937 (p. 372), "was the most important
step ever taken in embryology," and it seems unlikely that he is soon
to be contradicted.
In the same way as the embryology of the 20th century has retained
yet altered the 19th century concept of germ layers, so does it still bear
the clear marks of influence, however modified these may have become,
of the 19th century cell doctrine; to confirm this point, one has only
to regard the titles of many of the periodicals in which embryological
articles are now being published: The Journal of Cellular and Comparative Physiology; Experimental Cell Research; The Proceedings of the
Congresses of Cell Biology; and so forth. In fact, while our views of the
cell theory itself have, as other historians have pointed out (J. W. Wilson,
1944, 1947a, b; Baker, 1948, 1949, 1952, 1953, 1955), undergone a
process of gradual change, it may well be mainly by virtue of the
heritage of 19th century dogma that the word cell is such a frequent
biological term; yet much of what is being discussed by so-called cell
biologists impinges less on cells qua cells than on their mere constituents,
whether membranes and inclusions on the morphological side, or enzyme
systems on the functional. Indeed, some of the work on homogenates is
so far from cellular that it might more befittingly be called uncellular
biology or uncellular physiology.
But if the division of biology which today encompasses much of embryology is called cell biology, this results only partly from the proverbial