IX.
DEVELOPMENT OF THE TELEOSTEAN EGG
391
ovarian hilum. Near to the hilum, the cytoplasm is rich in proteins (Fig.
7). The axis joining the centre of the crescent to the centre of the oocyte
determines, with the axis of polarity, a plane which passes through the
ovarian hilum. Though these structures disappear during vitellogenesis,
it is possible to show by referring to the hilum, that this plane is the
future symmetry plane of the embryo, and that the crescent marks the
future dorsal side (Fautrez, 1953, Fautrez and Vakaet, 1954).
As the plasm of Vakaet is sub-cortical, it may remain intact during
the rearrangements if it only slides under the egg surface. Does it
represent the determining element (crescent) implied in the hypothesis of Oppenheimer and Tung? This question cannot be answered yet
in the affirmative.
However, the existence of a fixed relation between the symmetry
plane and the ovarian hilum has been denied in the egg of Lebistes by
Clavert and Filogamo (1957). If a symmetry plane does exist before the
phase of major growth it is impossible to trace it afterwards. And one
cannot be certain therefore that it corresponds to that of the embryo.
a. The Conception of Oppenheimer and Tung
Oppenheimer (1934, 1936) notes that the degree of differentiation of a
blastoderm in Fundulus, separated from its yolk and cultivated in
Holtfreter's solution, is a function of the stage at which it is put into
culture. If it is explanted before a so-called critical stage, the blastoderm turns into a hyperblastula; if it is explanted after that, it undergoes differentiation (Fig. 8). The critical stage corresponds to 8 blastomeres in Carassius (Tung et ah, 1945), 32 in Fundulus (Oppenheimer,
1936), and the young blástula in Salmo (Devillers, 1949). There is aparalwith the duration of development of the different species. The existence
of a critical stage is surely related to the realization of an essential pheno
menon of premorphogenesis. The yolk does not seem to intervene since
it is absent in all cases; though the quantity used before gastrulation is
very small, it is not negligible since the blastoderms of Salmo (Devillers,
1949; Devillers et ah, 1958), and Fundulus (Trinkaus, 1953; Trinkaus et
ah, 1956) completely deprived of their periblast cannot be cultivated
without an addition of glucose to the mineral medium. The periblast
cytoplasm therefore plays a special part; it supplies the 'materials'
indispensable for the determination of the marginal zone.
Oppenheimer's idea has been tested on the egg of Carassius (Tung
et ah, 1943, 1945), of Fundulus (Tung, 1955) and of Salmo (Devillers,
1951c).
Between the undivided stage and stage 8, Tung made latitudinal
lei between these stages and the ratio
cytoplasm volume as well as
yolk volume
DEVELOPMENT OF THE TELEOSTEAN EGG
391
ovarian hilum. Near to the hilum, the cytoplasm is rich in proteins (Fig.
7). The axis joining the centre of the crescent to the centre of the oocyte
determines, with the axis of polarity, a plane which passes through the
ovarian hilum. Though these structures disappear during vitellogenesis,
it is possible to show by referring to the hilum, that this plane is the
future symmetry plane of the embryo, and that the crescent marks the
future dorsal side (Fautrez, 1953, Fautrez and Vakaet, 1954).
As the plasm of Vakaet is sub-cortical, it may remain intact during
the rearrangements if it only slides under the egg surface. Does it
represent the determining element (crescent) implied in the hypothesis of Oppenheimer and Tung? This question cannot be answered yet
in the affirmative.
However, the existence of a fixed relation between the symmetry
plane and the ovarian hilum has been denied in the egg of Lebistes by
Clavert and Filogamo (1957). If a symmetry plane does exist before the
phase of major growth it is impossible to trace it afterwards. And one
cannot be certain therefore that it corresponds to that of the embryo.
a. The Conception of Oppenheimer and Tung
Oppenheimer (1934, 1936) notes that the degree of differentiation of a
blastoderm in Fundulus, separated from its yolk and cultivated in
Holtfreter's solution, is a function of the stage at which it is put into
culture. If it is explanted before a so-called critical stage, the blastoderm turns into a hyperblastula; if it is explanted after that, it undergoes differentiation (Fig. 8). The critical stage corresponds to 8 blastomeres in Carassius (Tung et ah, 1945), 32 in Fundulus (Oppenheimer,
1936), and the young blástula in Salmo (Devillers, 1949). There is aparalwith the duration of development of the different species. The existence
of a critical stage is surely related to the realization of an essential pheno
menon of premorphogenesis. The yolk does not seem to intervene since
it is absent in all cases; though the quantity used before gastrulation is
very small, it is not negligible since the blastoderms of Salmo (Devillers,
1949; Devillers et ah, 1958), and Fundulus (Trinkaus, 1953; Trinkaus et
ah, 1956) completely deprived of their periblast cannot be cultivated
without an addition of glucose to the mineral medium. The periblast
cytoplasm therefore plays a special part; it supplies the 'materials'
indispensable for the determination of the marginal zone.
Oppenheimer's idea has been tested on the egg of Carassius (Tung
et ah, 1943, 1945), of Fundulus (Tung, 1955) and of Salmo (Devillers,
1951c).
Between the undivided stage and stage 8, Tung made latitudinal
lei between these stages and the ratio
cytoplasm volume as well as
yolk volume