30
J. CLAVERT
the rest of the egg is occupied by a cytoplasmic mass which is less
pigmented than either the cortex or the brown central yolk. The egg
also contains small yolk granules, and various organelles (chondriome,
Golgi apparatus, ergastoplasm); the spherical yolk granules gradually
become smaller and less dense towards the animal pole. Ancel and
Vintemberger during much systematic research have never observed
asymmetry in the distribution of the different constituents of the
mature unfertilized egg. The constituents, evenly distributed along the
axis of polarity, give the egg a typical axial symmetry. The egg is
enclosed within a vitelline membrane in direct contact with the chorion.
It is similar in ultra-structure to all cellular membranes. A jelly-coat
formed in the oviduct after ovulation is attached to it.
2. Modifications of the Structure of the Egg after Fertilization;
Rotation of Fertilization
The mature egg is fertilized after ovulation by a spermatozoon which
remains attached to the egg membrane for about 10 minutes and then
takes about 15 to 20 minutes to penetrate. Fertilization is followed by a
series of reactions which make up the phenomena of activation. Among
these, we may note the movements of the infundibulum of maturation,
movements of the pigment which bring about the disappearance of the
superior polar spot, the rotation of orientation which brings the animalvegetal axis into a vertical position with respect to gravity, the
emission of a second polar body, and last, but not least, the rotation of
fertilization which ends in the formation of the grey crescent and thus
in the fixation of the plane of bilateral symmetry of the future embryo.
For the study of egg symmetrization, the formation of the grey
crescent is the most important stage, because of the irreversible
modifications it provokes. There is an earlier, primary, cortical reaction
(Ancel and Vintemberger, 1948), an initial shifting of pigments due to
an elevation and concentration of the cortical layer into the superior
pole of the egg; but this rearrangement is only temporary. The elements
soon return to their original place, leaving at most a slight pigmentary
asymmetry. Roux, under the term 'rotation of fertilization', described a
phenomenon consisting of the displacement of the egg en masse, bringing
the primary axis of polarity into an oblique position, the superior pole
descending in the future ventral hemisphere and the inferior pole
ascending in the future dorsal hemisphere (Roux, 1887; Schultze, 1899;
Vogt, 1928; Banki, 1927; Wintrebert, 1931). This conception was not
true, for Ancel and Vintemberger (1948) have shown by an ingenious
technique that the rotation of fertilization is not a rotation of the whole
mass of the egg, but only a rotation of the cortical layer round the
central elements. The study of the movement of electrolytic marks
J. CLAVERT
the rest of the egg is occupied by a cytoplasmic mass which is less
pigmented than either the cortex or the brown central yolk. The egg
also contains small yolk granules, and various organelles (chondriome,
Golgi apparatus, ergastoplasm); the spherical yolk granules gradually
become smaller and less dense towards the animal pole. Ancel and
Vintemberger during much systematic research have never observed
asymmetry in the distribution of the different constituents of the
mature unfertilized egg. The constituents, evenly distributed along the
axis of polarity, give the egg a typical axial symmetry. The egg is
enclosed within a vitelline membrane in direct contact with the chorion.
It is similar in ultra-structure to all cellular membranes. A jelly-coat
formed in the oviduct after ovulation is attached to it.
2. Modifications of the Structure of the Egg after Fertilization;
Rotation of Fertilization
The mature egg is fertilized after ovulation by a spermatozoon which
remains attached to the egg membrane for about 10 minutes and then
takes about 15 to 20 minutes to penetrate. Fertilization is followed by a
series of reactions which make up the phenomena of activation. Among
these, we may note the movements of the infundibulum of maturation,
movements of the pigment which bring about the disappearance of the
superior polar spot, the rotation of orientation which brings the animalvegetal axis into a vertical position with respect to gravity, the
emission of a second polar body, and last, but not least, the rotation of
fertilization which ends in the formation of the grey crescent and thus
in the fixation of the plane of bilateral symmetry of the future embryo.
For the study of egg symmetrization, the formation of the grey
crescent is the most important stage, because of the irreversible
modifications it provokes. There is an earlier, primary, cortical reaction
(Ancel and Vintemberger, 1948), an initial shifting of pigments due to
an elevation and concentration of the cortical layer into the superior
pole of the egg; but this rearrangement is only temporary. The elements
soon return to their original place, leaving at most a slight pigmentary
asymmetry. Roux, under the term 'rotation of fertilization', described a
phenomenon consisting of the displacement of the egg en masse, bringing
the primary axis of polarity into an oblique position, the superior pole
descending in the future ventral hemisphere and the inferior pole
ascending in the future dorsal hemisphere (Roux, 1887; Schultze, 1899;
Vogt, 1928; Banki, 1927; Wintrebert, 1931). This conception was not
true, for Ancel and Vintemberger (1948) have shown by an ingenious
technique that the rotation of fertilization is not a rotation of the whole
mass of the egg, but only a rotation of the cortical layer round the
central elements. The study of the movement of electrolytic marks