IX. DEVELOPMENT OF THE TELEOSTEAN EGG
399
or of the physico-chemical properties of the cortex in the maternal
organism. At laying, non-adhesivity is already acquired, while impermeability only sets in later, during activation.
During cortical differentiation, surface-active substances must accumulate at the surface (Gibbs-Thomson effect) and water must be able
to orientate their polar groups towards the outside, thus conferring
on the surface film an ordered structure which is propagated towards
the interior by the phenomenon of epitaxis. Ca
++ (or bivalent electrolytes) through its bivalency could act by joining the acid groups of
phosphatides and of nucleic acids (Monné, 1946).
The essential organization must be finished in the maternal organism :
the ions of the water in which the eggs are laid do not come into play,
since the cortex of eggs laid in doubly distilled water shows its characteristic properties.
On the other hand, the cortex appears, at least in Teleosts, as a
primary differentiation which cannot regenerate. The walls of the deep
blastomeres, cultivated in isotonic solutions, never acquire the properties of the cortex; the enveloping layer, after excision, is never
formed again (Devillers et al., 1957b). In Amphibia, Holtfreter (1943a)
considers that the possibility of forming a coat is specific to certain cell
categories (ecto- and endoderm); on the other hand, if the coat is
artificially disintegrated, it can be reformed by action of the medium on
the cellular surface. There is therefore an important difference, still
unexplained, between the two types of eggs.
Under external influences, the structure and properties of the cortex
can be modified temporarily or permanently. This must be taken into
account when interpreting results on permeability in non-physiological
media.
A simple mechanical stirring of the isolated cortex of Fundulus
causes its dissolution in physiological solution, which leads Trinkaus
(1948, 1949b) to consider it as a thixotropic system.
If Ca
++ plays a part very early in the organization of the cortex, it is
no longer absolutely necessary for the maintenance of its structure. The
eggs of Salmo (Devillers, 1948a), Oryzias (Yamamoto, 1941) or Fundulus
(Loeb, 1894, 1900, quoted by Yamamoto, 1941) develop in doubly
distilled water. As for monovalent ions, they can slowly dissociate the
cortex: when reared in Holtfreter's solution twice concentrated and
lacking Ca
+ +
, the egg of Salmo undergoes separation of its blastomeres
(Devillers, 1948a; Trinkaus, 1949b, on Fundulus in sea-water without
Ca); citrates and oxalates, which fix Ca
+ +
, have the same effect.
Raising the pH to 9-11-4 causes a rapid cortical dissociation, the
blastoderm bursts and the blastomeres disperse but survive for a few
days in this medium, which indicates that there is a structural difference
399
or of the physico-chemical properties of the cortex in the maternal
organism. At laying, non-adhesivity is already acquired, while impermeability only sets in later, during activation.
During cortical differentiation, surface-active substances must accumulate at the surface (Gibbs-Thomson effect) and water must be able
to orientate their polar groups towards the outside, thus conferring
on the surface film an ordered structure which is propagated towards
the interior by the phenomenon of epitaxis. Ca
++ (or bivalent electrolytes) through its bivalency could act by joining the acid groups of
phosphatides and of nucleic acids (Monné, 1946).
The essential organization must be finished in the maternal organism :
the ions of the water in which the eggs are laid do not come into play,
since the cortex of eggs laid in doubly distilled water shows its characteristic properties.
On the other hand, the cortex appears, at least in Teleosts, as a
primary differentiation which cannot regenerate. The walls of the deep
blastomeres, cultivated in isotonic solutions, never acquire the properties of the cortex; the enveloping layer, after excision, is never
formed again (Devillers et al., 1957b). In Amphibia, Holtfreter (1943a)
considers that the possibility of forming a coat is specific to certain cell
categories (ecto- and endoderm); on the other hand, if the coat is
artificially disintegrated, it can be reformed by action of the medium on
the cellular surface. There is therefore an important difference, still
unexplained, between the two types of eggs.
Under external influences, the structure and properties of the cortex
can be modified temporarily or permanently. This must be taken into
account when interpreting results on permeability in non-physiological
media.
A simple mechanical stirring of the isolated cortex of Fundulus
causes its dissolution in physiological solution, which leads Trinkaus
(1948, 1949b) to consider it as a thixotropic system.
If Ca
++ plays a part very early in the organization of the cortex, it is
no longer absolutely necessary for the maintenance of its structure. The
eggs of Salmo (Devillers, 1948a), Oryzias (Yamamoto, 1941) or Fundulus
(Loeb, 1894, 1900, quoted by Yamamoto, 1941) develop in doubly
distilled water. As for monovalent ions, they can slowly dissociate the
cortex: when reared in Holtfreter's solution twice concentrated and
lacking Ca
+ +
, the egg of Salmo undergoes separation of its blastomeres
(Devillers, 1948a; Trinkaus, 1949b, on Fundulus in sea-water without
Ca); citrates and oxalates, which fix Ca
+ +
, have the same effect.
Raising the pH to 9-11-4 causes a rapid cortical dissociation, the
blastoderm bursts and the blastomeres disperse but survive for a few
days in this medium, which indicates that there is a structural difference