TWENTIETH CENTURY EMBRYOLOGICAL CONCEPTS
25
as for the supracellular coat, it is in a way far less significant that in
1956 Spratt, after Holtfreter, sees intercellular bridges in the chick
blastoderm than that Rhumbler (1899, 1902) believed the amphibian
egg to be invested with a special coat whose mechanical functions had
to be taken into account in connection with the displacements of cells
during invagination, or than that in 1897 Andrews not only observed and
described intercellular bridges in the echinoderm egg (Andrews, 1897a)
but recognized them for quite what they are worth today (Andrews,
1897b, p. 87):
"The true nature and mode of formation of cell walls seem to be
that they are but pellicular modifications of the continuous substance of masses into plates, which are as readily formed internally
as externally, that they do not differ either in origin or constitution
from other internal and external pellicles or ectosarcal formations;
that they are, in short, not substance dividers nor substance isolators,
but substance structures, substance differentiators,
and
differentiations, substance organs; and finally, that they belong primarily to
the mass and but secondarily to cells.
We can no longer regard these formations as having for the living
substance the value of a prison wall. We must look upon them as
substance strengthened;
as devices for securing a qualified independence for areas which yet maintain absolute physical and physiological continuity. . . . Cell division is mass differentiation; that is its
true meaning—making
it one with all the host of substance
organizations of the elements of the living substance for physiological
function." (Italics those of the original author.)
Finally, if the 20th century views the cell as a unit of embryonic
function both in its own right and as subservient to the total mass of cells
constituting the whole embryo, a primary importance of the contemporary work on a conceptual plane is that it seems at last once more to be
reconsidering the interrelationships of cells as such to each other in
other ways than from the sole point of view of induction. The reversion
of attention towards supracellular protoplasmic coats and intercellular
bridges is only one example of this tendency. Another is the present
ruling emphasis on affinity as a fundamental principle in development,
and it is making no new and profound revelation to say that modern
study of cell-to-cell relationships in development now hangs heavily on
concepts of affinity, thanks once more to the insight of Holtfreter (1939).
The history of the concepts of affinity in biology is another fascinating
chapter not yet written. These ideas must certainly have been intimately
25
as for the supracellular coat, it is in a way far less significant that in
1956 Spratt, after Holtfreter, sees intercellular bridges in the chick
blastoderm than that Rhumbler (1899, 1902) believed the amphibian
egg to be invested with a special coat whose mechanical functions had
to be taken into account in connection with the displacements of cells
during invagination, or than that in 1897 Andrews not only observed and
described intercellular bridges in the echinoderm egg (Andrews, 1897a)
but recognized them for quite what they are worth today (Andrews,
1897b, p. 87):
"The true nature and mode of formation of cell walls seem to be
that they are but pellicular modifications of the continuous substance of masses into plates, which are as readily formed internally
as externally, that they do not differ either in origin or constitution
from other internal and external pellicles or ectosarcal formations;
that they are, in short, not substance dividers nor substance isolators,
but substance structures, substance differentiators,
and
differentiations, substance organs; and finally, that they belong primarily to
the mass and but secondarily to cells.
We can no longer regard these formations as having for the living
substance the value of a prison wall. We must look upon them as
substance strengthened;
as devices for securing a qualified independence for areas which yet maintain absolute physical and physiological continuity. . . . Cell division is mass differentiation; that is its
true meaning—making
it one with all the host of substance
organizations of the elements of the living substance for physiological
function." (Italics those of the original author.)
Finally, if the 20th century views the cell as a unit of embryonic
function both in its own right and as subservient to the total mass of cells
constituting the whole embryo, a primary importance of the contemporary work on a conceptual plane is that it seems at last once more to be
reconsidering the interrelationships of cells as such to each other in
other ways than from the sole point of view of induction. The reversion
of attention towards supracellular protoplasmic coats and intercellular
bridges is only one example of this tendency. Another is the present
ruling emphasis on affinity as a fundamental principle in development,
and it is making no new and profound revelation to say that modern
study of cell-to-cell relationships in development now hangs heavily on
concepts of affinity, thanks once more to the insight of Holtfreter (1939).
The history of the concepts of affinity in biology is another fascinating
chapter not yet written. These ideas must certainly have been intimately