VITELLINE MEMBRANE AND CORTICAL PARTICLES 225
7). When antisera which only contained antibodies against heat-labile
antigens were used, the ferritin label was confined to limited regions on
the vitelline membrane. This seems also to indicate that there are certain local differences in the vitelline membrane—these may be in relation to the mutual distribution of the two components that have been
distinguished morphologically.
The vitelline membrane in the mature unfertilized eggs is evidently
rather elastic. The vitelline membrane was seen to shrink when it was
released from the egg surface, for example, after treatment with sperm
lysin and subsequent transfer to 50% diluted sea water (Runnström
et al., 1945). The elasticity is in keeping with the presence of the fibrous
proteins which may have the tendency to assume a more coiled conformation. The vitelline membrane does not show any birefringence. This
tends to show that, even under normal extension, there is no high degree of orientation of the constituent macromolecules.
A considerably thicker layer than the limiting plasma membrane is
referred to as "cortex-" or "cortical layer." It is considered to have a
higher consistency than the interior of the egg (Chambers, 1921). Somewhat varying values have been assigned to the thickness of the cortex.
In a careful investigation, Hiramoto (1957) found the value of 3 μ in
the eggs of Hemicentrotus
pulcherrimus.
This value may be subject to
variation according to the species under investigation. Mercer and Wolpert (1962) pointed out that their electron-microscopic observation fails
to demonstrate a well-defined cortical layer. Moreover they observed
that, in centrifuged eggs, inclusions such as yolk granules or mitochondria may penetrate the alleged cortical layer to contact the plasma membrane. However, the cortex of the heavier region of an egg subjected
to centrifugation may not be typical for the cortex as a whole. The
thickness of the cortex may be lowered by a weak centripetal displacement of the cortical layer. Moreover, the granules may be able temporarily to break up certain bonds responsible for the gel character of the
cortex (see Runnström and Kriszat, 1950a).
It must be admitted that a sharp delimitation of the cortex is very
difficult. In the oocytes there is a region about 1 μ thick that is relatively
free from yolk granules and mitochondria but rich in endoplasmic vesicles. Moreover, the numerous villi belong to the cortical layer (see
Lönning, 1964, Figs. 1 and 2). These are very dynamic structures that
may enlarge and decrease. The reception cones formed after sperm attachment in oocytes (for references see Runnström, 1963a) or in mature
eggs may be regarded as united villi.
The surface of the oocytes shows an absent or very weak birefringence
(Monroy, 1948). After the oocytes have been transferred to a hypertonic
7). When antisera which only contained antibodies against heat-labile
antigens were used, the ferritin label was confined to limited regions on
the vitelline membrane. This seems also to indicate that there are certain local differences in the vitelline membrane—these may be in relation to the mutual distribution of the two components that have been
distinguished morphologically.
The vitelline membrane in the mature unfertilized eggs is evidently
rather elastic. The vitelline membrane was seen to shrink when it was
released from the egg surface, for example, after treatment with sperm
lysin and subsequent transfer to 50% diluted sea water (Runnström
et al., 1945). The elasticity is in keeping with the presence of the fibrous
proteins which may have the tendency to assume a more coiled conformation. The vitelline membrane does not show any birefringence. This
tends to show that, even under normal extension, there is no high degree of orientation of the constituent macromolecules.
A considerably thicker layer than the limiting plasma membrane is
referred to as "cortex-" or "cortical layer." It is considered to have a
higher consistency than the interior of the egg (Chambers, 1921). Somewhat varying values have been assigned to the thickness of the cortex.
In a careful investigation, Hiramoto (1957) found the value of 3 μ in
the eggs of Hemicentrotus
pulcherrimus.
This value may be subject to
variation according to the species under investigation. Mercer and Wolpert (1962) pointed out that their electron-microscopic observation fails
to demonstrate a well-defined cortical layer. Moreover they observed
that, in centrifuged eggs, inclusions such as yolk granules or mitochondria may penetrate the alleged cortical layer to contact the plasma membrane. However, the cortex of the heavier region of an egg subjected
to centrifugation may not be typical for the cortex as a whole. The
thickness of the cortex may be lowered by a weak centripetal displacement of the cortical layer. Moreover, the granules may be able temporarily to break up certain bonds responsible for the gel character of the
cortex (see Runnström and Kriszat, 1950a).
It must be admitted that a sharp delimitation of the cortex is very
difficult. In the oocytes there is a region about 1 μ thick that is relatively
free from yolk granules and mitochondria but rich in endoplasmic vesicles. Moreover, the numerous villi belong to the cortical layer (see
Lönning, 1964, Figs. 1 and 2). These are very dynamic structures that
may enlarge and decrease. The reception cones formed after sperm attachment in oocytes (for references see Runnström, 1963a) or in mature
eggs may be regarded as united villi.
The surface of the oocytes shows an absent or very weak birefringence
(Monroy, 1948). After the oocytes have been transferred to a hypertonic