386
JEAN J. PASTEELS
Unfortunately, the structure of the 'dorsal' or Ventral' cortex has
not been examined so far.
The vesicular subcortical layer of the animal pole, which has a
thickness of 0-3 to 0-5 μ (Dollander) has tentatively been assimilated to
the plasmagel of Marsland. Undoubtedly it corresponds to the ribonucleic acid layer which is detectable by histochemistry and was studied
by Ledoux et al. (1955) in connection with the effects of ribonuclease.
The existence of this layer is restricted to the animal pole and it is
progressively built up after fertilization. Definite information is still
lacking about the dramatic structural changes which may arise when
symmetrization appears, and which could be responsible for the dorsoventral cortical field.
IX. The'Coat'of Holtfreter
Holtfreter has defined the 'coat' by several properties : its appearance
after fertilization, its contractility and non-adhesiveness, its ability to
connect the superficial cells of the blastula or the gastrula. The 'coat' is
considered by Holtfreter to be supracellular.
The electron microscope has led Dollander, confirmed by Wartenberg
and Schmidt, to a different conclusion : there is no supracellular cortical
structure. Wartenberg and Schmidt come to the conclusion that the
'coat' can be identified with the vesicular subcortical layer. Dollander
expresses the judicious opinion that the concept of 'coat', as it was used
by Holtfreter, is nothing but a logical artefact in the sense that several
properties obviously depending on different structures, have been
attributed to the same hypothetical structure. Contractility and nonadhesiveness belong to the plasmalemma plus the subcortical layer;
connections between the surfaces of blastomeres and cells of the blastula
and of the gastrula are secured by desmosomes which rapidly appear
between neighbouring cells. Further work about the evolution of this
structure was recently reviewed by Dollander (1962).
X. Summary and Conclusions
We may summarize :
1. the positive evidence concerning the morphogenetic
role of the egg
cortex of the amphibians,
and
2. some still unresolved problems that call for investigation
in the near
future :
1. (a) By cortex we must mean: plasmalemma plus some underlying cytoplasm.
JEAN J. PASTEELS
Unfortunately, the structure of the 'dorsal' or Ventral' cortex has
not been examined so far.
The vesicular subcortical layer of the animal pole, which has a
thickness of 0-3 to 0-5 μ (Dollander) has tentatively been assimilated to
the plasmagel of Marsland. Undoubtedly it corresponds to the ribonucleic acid layer which is detectable by histochemistry and was studied
by Ledoux et al. (1955) in connection with the effects of ribonuclease.
The existence of this layer is restricted to the animal pole and it is
progressively built up after fertilization. Definite information is still
lacking about the dramatic structural changes which may arise when
symmetrization appears, and which could be responsible for the dorsoventral cortical field.
IX. The'Coat'of Holtfreter
Holtfreter has defined the 'coat' by several properties : its appearance
after fertilization, its contractility and non-adhesiveness, its ability to
connect the superficial cells of the blastula or the gastrula. The 'coat' is
considered by Holtfreter to be supracellular.
The electron microscope has led Dollander, confirmed by Wartenberg
and Schmidt, to a different conclusion : there is no supracellular cortical
structure. Wartenberg and Schmidt come to the conclusion that the
'coat' can be identified with the vesicular subcortical layer. Dollander
expresses the judicious opinion that the concept of 'coat', as it was used
by Holtfreter, is nothing but a logical artefact in the sense that several
properties obviously depending on different structures, have been
attributed to the same hypothetical structure. Contractility and nonadhesiveness belong to the plasmalemma plus the subcortical layer;
connections between the surfaces of blastomeres and cells of the blastula
and of the gastrula are secured by desmosomes which rapidly appear
between neighbouring cells. Further work about the evolution of this
structure was recently reviewed by Dollander (1962).
X. Summary and Conclusions
We may summarize :
1. the positive evidence concerning the morphogenetic
role of the egg
cortex of the amphibians,
and
2. some still unresolved problems that call for investigation
in the near
future :
1. (a) By cortex we must mean: plasmalemma plus some underlying cytoplasm.