VITELLINE MEMBRANE AND CORTICAL PARTICLES 255
larger containing the germinal vesicle and one that contained the surface
layer of oocyte. The diagrammatic Fig. 22 gives a view of the changes.
In the upper part containing the germinal vesicle a certain parallel order is seen in the cytoplasm. The lower part consists of the surface layer
and may be folded or furnished with tubular protrusions. The lower
part is also surrounded by the strongly folded vitelline layer (see Section I,A). The following observation proves that the lower region in Fig.
22 really corresponds to the surface layer of the cell. The oocytes were
heavily inseminated and only then transferred to the sea water with
periodate. Numerous spermatozoa which had attached themselves to the
cytoplasmic surface of the oocytes were all displaced to the lower end of
the oocyte. The whole vitelline membrane also followed the displacement.
In Fig. 22 this appears folded, and several spermatozoa are attached to
the membrane. Despite the displacement of the surface layer, the semipermeability of the plasma membrane seems to be undisturbed. Otherwise, a cytolysis should have occurred, at least in the hypertonic medium.
Periodate-treated oocytes were fixed in osmic acid in sea water (pH
ca. 8). It was then evident that the fine striation indicated in Fig. 22 is
caused by a stretching of endoplasmic vesicles. The striated region contains very few cortical particles and yolk globules, whereas these are
strongly aggregated in the surface zone (Fig. 22, si).
The mitochondria are aggregated into rather large groups which are
found in the zone of endoplasmic vesicles and also at the basis of the
bulges of the surface zone. Single mitochondria may also be enclosed
between the yolk globules of this zone. The mitochondria are in a dispersed state in the normal oocytes but aggregate after the maturation of
the egg (see Afzelius, 1956). The periodate treatment has thus an effect
similar to that of maturation.
The observations described above (Runnström, unpublished data,
1963) show an experimentally provoked phase separation in which
the cortical particles show their compatibility with the cytoplasm
of the cell surface, whereas before the periodate treatment they
are compatible with the endoplasm. The results presented thus seem to
demonstrate a shift in partition of cortical particles before and after
periodate treatment. A parallel shift may occur upon maturation of the
oocyte. In the periodate-treated oocytes the mitochondria also separate
from the bulk of the cytoplasm. Evidence from electron micrographs
gives preference to the view that it is a special cytoplasm surrounding
the mitochondria which separates out rather than the mitochondria themselves. These should then have been more densely aggregated than was
actually the case. Instead, they seem to be suspended in separate islands
of cytoplasm.
larger containing the germinal vesicle and one that contained the surface
layer of oocyte. The diagrammatic Fig. 22 gives a view of the changes.
In the upper part containing the germinal vesicle a certain parallel order is seen in the cytoplasm. The lower part consists of the surface layer
and may be folded or furnished with tubular protrusions. The lower
part is also surrounded by the strongly folded vitelline layer (see Section I,A). The following observation proves that the lower region in Fig.
22 really corresponds to the surface layer of the cell. The oocytes were
heavily inseminated and only then transferred to the sea water with
periodate. Numerous spermatozoa which had attached themselves to the
cytoplasmic surface of the oocytes were all displaced to the lower end of
the oocyte. The whole vitelline membrane also followed the displacement.
In Fig. 22 this appears folded, and several spermatozoa are attached to
the membrane. Despite the displacement of the surface layer, the semipermeability of the plasma membrane seems to be undisturbed. Otherwise, a cytolysis should have occurred, at least in the hypertonic medium.
Periodate-treated oocytes were fixed in osmic acid in sea water (pH
ca. 8). It was then evident that the fine striation indicated in Fig. 22 is
caused by a stretching of endoplasmic vesicles. The striated region contains very few cortical particles and yolk globules, whereas these are
strongly aggregated in the surface zone (Fig. 22, si).
The mitochondria are aggregated into rather large groups which are
found in the zone of endoplasmic vesicles and also at the basis of the
bulges of the surface zone. Single mitochondria may also be enclosed
between the yolk globules of this zone. The mitochondria are in a dispersed state in the normal oocytes but aggregate after the maturation of
the egg (see Afzelius, 1956). The periodate treatment has thus an effect
similar to that of maturation.
The observations described above (Runnström, unpublished data,
1963) show an experimentally provoked phase separation in which
the cortical particles show their compatibility with the cytoplasm
of the cell surface, whereas before the periodate treatment they
are compatible with the endoplasm. The results presented thus seem to
demonstrate a shift in partition of cortical particles before and after
periodate treatment. A parallel shift may occur upon maturation of the
oocyte. In the periodate-treated oocytes the mitochondria also separate
from the bulk of the cytoplasm. Evidence from electron micrographs
gives preference to the view that it is a special cytoplasm surrounding
the mitochondria which separates out rather than the mitochondria themselves. These should then have been more densely aggregated than was
actually the case. Instead, they seem to be suspended in separate islands
of cytoplasm.