IX. DEVELOPMENT OF THE TELEOSTEAN EGG
403
By acting on the structure of the covering, different media alter
healing. Monovalent ions in isotonic solution (NaCl at 0-7 per cent) or
increase of pH stop, in a reversible way, the movements created by a
wound, acting just as they do on epiboly. CaCl 2 increases cortical
rigidity and reinforces its mechanical properties (cf. Chambers, 1942,
on sea-urchin egg). This substance is not absolutely necessary for the
closing movement since the wound in Fundulus heals in distilled water
(Trinkaus, 1949b), but in Salmo it does not; the cortical movements are
not strong enough in this case to oppose themselves to the enlargement
of the wound by turgescence of the cytoplasm. One can reinforce these
movements by adding CaCl 2 (0-04 per cent) or establish isotonism by
adding glycerin (22 per cent); the wound then heals in these abnormal
media.
The mechanical properties of the cortex therefore vary from one
genus to another. The cortical movements are less vigorous in Lebistes
and Platypoecilus than in Fundulus (Trinkaus, 1949b).
e. The Role of the Cortex in the Cleaved Blastoderm
When the blastoderm undergoes cleavage, is the cortex broken
between the surface blastomeres (forming their exterior walls) or does it
keep its continuity and, like the coat of Amphibia, go from one blastomere to another without interruption? Neither studies in vivo, nor by
means of sections, allows us to decide yet.
In any case, the surface blastomeres, solidly linked one to another,
form a unitary structure. The enveloping layer, in a cellular state, has
the same properties as the cortex of the undivided egg, since its surface
is formed by the former cortex, whether broken up or intact. On the
contrary, the deep blastomeres behave like a collection of independent
cells.
The integration of the surface blastomeres in a whole cortex is very
important for the succeeding development. Any movement, whether it
comes from the activity of the cortex itself or from a group of blastomeres, will spread to the entire enveloping layer, producing there
co-ordinated movements. Here again we come across the co-ordinating
role of the 'coat' shown by Holtfreter (1943a) in Amphibia.
The osmoregulative and mechanical properties give the enveloping
layer a directing role in morphogenesis towards the more passive mass of
deep blastomeres. The relations found at the pluricellular level are the
same as those existing between membrane and endoplasm (Holtfreter,
1948) in the cell.
A surface wound heals by movements of the enveloping layer that are
similar to those of the undivided cortex (see also the healing of epithelial wounds, Wilbur and Chambers, 1942). The stretching of the
O
A.M. I
403
By acting on the structure of the covering, different media alter
healing. Monovalent ions in isotonic solution (NaCl at 0-7 per cent) or
increase of pH stop, in a reversible way, the movements created by a
wound, acting just as they do on epiboly. CaCl 2 increases cortical
rigidity and reinforces its mechanical properties (cf. Chambers, 1942,
on sea-urchin egg). This substance is not absolutely necessary for the
closing movement since the wound in Fundulus heals in distilled water
(Trinkaus, 1949b), but in Salmo it does not; the cortical movements are
not strong enough in this case to oppose themselves to the enlargement
of the wound by turgescence of the cytoplasm. One can reinforce these
movements by adding CaCl 2 (0-04 per cent) or establish isotonism by
adding glycerin (22 per cent); the wound then heals in these abnormal
media.
The mechanical properties of the cortex therefore vary from one
genus to another. The cortical movements are less vigorous in Lebistes
and Platypoecilus than in Fundulus (Trinkaus, 1949b).
e. The Role of the Cortex in the Cleaved Blastoderm
When the blastoderm undergoes cleavage, is the cortex broken
between the surface blastomeres (forming their exterior walls) or does it
keep its continuity and, like the coat of Amphibia, go from one blastomere to another without interruption? Neither studies in vivo, nor by
means of sections, allows us to decide yet.
In any case, the surface blastomeres, solidly linked one to another,
form a unitary structure. The enveloping layer, in a cellular state, has
the same properties as the cortex of the undivided egg, since its surface
is formed by the former cortex, whether broken up or intact. On the
contrary, the deep blastomeres behave like a collection of independent
cells.
The integration of the surface blastomeres in a whole cortex is very
important for the succeeding development. Any movement, whether it
comes from the activity of the cortex itself or from a group of blastomeres, will spread to the entire enveloping layer, producing there
co-ordinated movements. Here again we come across the co-ordinating
role of the 'coat' shown by Holtfreter (1943a) in Amphibia.
The osmoregulative and mechanical properties give the enveloping
layer a directing role in morphogenesis towards the more passive mass of
deep blastomeres. The relations found at the pluricellular level are the
same as those existing between membrane and endoplasm (Holtfreter,
1948) in the cell.
A surface wound heals by movements of the enveloping layer that are
similar to those of the undivided cortex (see also the healing of epithelial wounds, Wilbur and Chambers, 1942). The stretching of the
O
A.M. I