IX. DEVELOPMENT OF THE TELEOSTEAN EGG
387
and bivalent ions at M/10, reversibly stop bipolar differentiation in the
egg of Salmo (but not that of Oryzias, Yamamoto, 1939; Carassius,
Yamamoto, 1954b; Gasterosteus, or Perca, Thomopoulos, 1953a, b). When
replaced in fresh water, the germ undergoes normal organization.
Actually, after laying, there is only a short period of cortical permeability (see Section III, C) during which water and ions can penetrate;
afterwards, the cortex becomes impermeable; thus there cannot be,
during the whole process of activation, a continuous inflow of ions
which would be necessary to create a diffusion potential.
Many methods are used to release activation (see reviews by Kanoh,
1953, 1957, and Yamamoto, 1945); but it is difficult to find out whether
they act in the same way.
The halting of bipolar differentiation in the maternal organism is
perhaps the result of a gelification of the cytoplasm due to an excess of
certain ions drawn from the maternal internal medium, these ions
causing a molecular condensation (Runnström et al. on sea-urchin egg,
1943). Does activation imply, as we have supposed (Devillers et al.,
1953a), a 'purifying' reaction which rids the egg of its excess ions? (See
Hayes et al., 1946; Kanoh, 1956.) It is difficult to apply this hypothesis
to marine eggs or even to all the fresh water eggs that do not react in the
same way to contact with water.
Activation is not limited to this resumption of cytoplasmic mobilization, but involves other phenomena which require the presence of Ca
+ +
.
Ions in the environment are not needed because the egg uses Ca released
by the cortex at stimulation; if this Ca is fixed beforehand by oxalate or
versene, there is no activation (Yamamoto, 1939, 1954a; Detlaf, 1958,
1959). Yamamoto takes up Heilbrunn's theory and suggests that
stimulation of the egg releases Ca from the cortex and that this Ca is
fixed by the inner cytoplasm. Ca plays no part in this first phase but has
a favourable action in the second phase, that of the propagation of the
wave of fertilization which causes the breaking of the alveolae (see
Section III, C, 1). It must be noted that Detlaf (1958), working on the
egg of Acipenser, comes to the the opposite conclusion: Ca is necessary
in the first phase, that of the stimulation of the spermatozoon, but not in
the second (see also Yanagimachi et al., 1953, on Clupea). The problem
has not yet been satisfactorily solved.
(5) All the mechanisms that we have mentioned so far are based on
the activity of the endoplasm. But for a number of authors (Seifriz,
1953; Holtfreter, 1948) cellular motility is due to the activity of the
ectoplasm, and Lewis (1949a, b) thinks that the 'cortical gel layer'
movements are responsible for bipolar differentiation. This conception
seems to have more arguments in its favour than the others.
In the course of bipolar differentiation, the egg of Brachydanio (as
387
and bivalent ions at M/10, reversibly stop bipolar differentiation in the
egg of Salmo (but not that of Oryzias, Yamamoto, 1939; Carassius,
Yamamoto, 1954b; Gasterosteus, or Perca, Thomopoulos, 1953a, b). When
replaced in fresh water, the germ undergoes normal organization.
Actually, after laying, there is only a short period of cortical permeability (see Section III, C) during which water and ions can penetrate;
afterwards, the cortex becomes impermeable; thus there cannot be,
during the whole process of activation, a continuous inflow of ions
which would be necessary to create a diffusion potential.
Many methods are used to release activation (see reviews by Kanoh,
1953, 1957, and Yamamoto, 1945); but it is difficult to find out whether
they act in the same way.
The halting of bipolar differentiation in the maternal organism is
perhaps the result of a gelification of the cytoplasm due to an excess of
certain ions drawn from the maternal internal medium, these ions
causing a molecular condensation (Runnström et al. on sea-urchin egg,
1943). Does activation imply, as we have supposed (Devillers et al.,
1953a), a 'purifying' reaction which rids the egg of its excess ions? (See
Hayes et al., 1946; Kanoh, 1956.) It is difficult to apply this hypothesis
to marine eggs or even to all the fresh water eggs that do not react in the
same way to contact with water.
Activation is not limited to this resumption of cytoplasmic mobilization, but involves other phenomena which require the presence of Ca
+ +
.
Ions in the environment are not needed because the egg uses Ca released
by the cortex at stimulation; if this Ca is fixed beforehand by oxalate or
versene, there is no activation (Yamamoto, 1939, 1954a; Detlaf, 1958,
1959). Yamamoto takes up Heilbrunn's theory and suggests that
stimulation of the egg releases Ca from the cortex and that this Ca is
fixed by the inner cytoplasm. Ca plays no part in this first phase but has
a favourable action in the second phase, that of the propagation of the
wave of fertilization which causes the breaking of the alveolae (see
Section III, C, 1). It must be noted that Detlaf (1958), working on the
egg of Acipenser, comes to the the opposite conclusion: Ca is necessary
in the first phase, that of the stimulation of the spermatozoon, but not in
the second (see also Yanagimachi et al., 1953, on Clupea). The problem
has not yet been satisfactorily solved.
(5) All the mechanisms that we have mentioned so far are based on
the activity of the endoplasm. But for a number of authors (Seifriz,
1953; Holtfreter, 1948) cellular motility is due to the activity of the
ectoplasm, and Lewis (1949a, b) thinks that the 'cortical gel layer'
movements are responsible for bipolar differentiation. This conception
seems to have more arguments in its favour than the others.
In the course of bipolar differentiation, the egg of Brachydanio (as