268
JOHN RUNNSTRÖM
1956). The subject was reviewed by Runnström et al. (1959, pp. 367370).
Before entering upon further discussion of the nature of the impulse
it should be stated that some phase in the activation process can be
followed by observing the egg with dark-field illumination (Runnström,
1923, 1928a). The mature unfertilized egg exhibits a yellow-orange color
on its surface. After effective attachment of the spermatozoon, there
is a change of the color to a brighter white. The color change propagates
from the point of sperm attachment over the whole egg surface; it coincides with the opening of the cortical particles. Runnström (1928a) considered the surface color viewed on dark field as an interference phenomenon depending on the thickness of a lipid layer. In protrusions from
an unfertilized egg, the Newton colors of first order could be seen going
successively from orange at the base of the protrusion to yellow, white,
and dark in the more distal region of the protrusion.
The color indicating greater thickness of the surface layer is due to
the presence of two lipoprotein layers—that of the plasma membrane
and that of the cortical particles. When these latter open up, the thickness is reduced to the thickness of one plasma membrane ; this makes the
color "sink" from orange to white. At the same time, however, the surface area of the egg increases due to formation of villi; this causes an
increase in light scattering. It follows from Section I,A that a process
takes place at maturation that is opposite to that occurring at fertilization. There may be certain variations in the hue of the color of the unfertilized egg. It may be more grayish or more brilliant. The latter was
observed particularly in eggs that had sustained an incomplete activation that led to some change in the cortex but was not sufficient to bring
about a general opening of the cortical particles. The color change in
the surface layers was not strictly parallel with the elevation of the fertilization membrane. Even when this membrane was rather close to the
egg surface the color change took place. At the distal pole the color
changes may precede considerably the full elevation of the fertilization
membrane. The color change may be incomplete, the full shift in color
taking place only in a region around the site of effective sperm attachment, and the rest of the surface may have an intermediate color. This
means probably that in this region only a certain fraction of the cortical
particle has opened up.
It has been pointed out in Section ΙΙ,Α that the plasma membrane is
involved in the impulse. This may mean a structural change which increases permeability, e.g., to ions. However, not only the plasma membrane may change, but also the membranes of the cortical particles, or
at least the region of this membrane which contributes to the formation
JOHN RUNNSTRÖM
1956). The subject was reviewed by Runnström et al. (1959, pp. 367370).
Before entering upon further discussion of the nature of the impulse
it should be stated that some phase in the activation process can be
followed by observing the egg with dark-field illumination (Runnström,
1923, 1928a). The mature unfertilized egg exhibits a yellow-orange color
on its surface. After effective attachment of the spermatozoon, there
is a change of the color to a brighter white. The color change propagates
from the point of sperm attachment over the whole egg surface; it coincides with the opening of the cortical particles. Runnström (1928a) considered the surface color viewed on dark field as an interference phenomenon depending on the thickness of a lipid layer. In protrusions from
an unfertilized egg, the Newton colors of first order could be seen going
successively from orange at the base of the protrusion to yellow, white,
and dark in the more distal region of the protrusion.
The color indicating greater thickness of the surface layer is due to
the presence of two lipoprotein layers—that of the plasma membrane
and that of the cortical particles. When these latter open up, the thickness is reduced to the thickness of one plasma membrane ; this makes the
color "sink" from orange to white. At the same time, however, the surface area of the egg increases due to formation of villi; this causes an
increase in light scattering. It follows from Section I,A that a process
takes place at maturation that is opposite to that occurring at fertilization. There may be certain variations in the hue of the color of the unfertilized egg. It may be more grayish or more brilliant. The latter was
observed particularly in eggs that had sustained an incomplete activation that led to some change in the cortex but was not sufficient to bring
about a general opening of the cortical particles. The color change in
the surface layers was not strictly parallel with the elevation of the fertilization membrane. Even when this membrane was rather close to the
egg surface the color change took place. At the distal pole the color
changes may precede considerably the full elevation of the fertilization
membrane. The color change may be incomplete, the full shift in color
taking place only in a region around the site of effective sperm attachment, and the rest of the surface may have an intermediate color. This
means probably that in this region only a certain fraction of the cortical
particle has opened up.
It has been pointed out in Section ΙΙ,Α that the plasma membrane is
involved in the impulse. This may mean a structural change which increases permeability, e.g., to ions. However, not only the plasma membrane may change, but also the membranes of the cortical particles, or
at least the region of this membrane which contributes to the formation