VITELLINE MEMBRANE AND CORTICAL PARTICLES 227
upon maturation, changes also take place in the jelly coat. After maturation the jelly becomes more sensitive to a depolymerizing effect of
added spermatozoa (see Runnström, 1964). The relation between these
phenomena is, however, not clear.
In the living mature egg a certain tangential orientation of fibrillar
material is observed even below the cortex proper. When the sea water
surrounding the eggs gradually becomes hypertonic because of evaporation, a negative birefringence of the fibrillar elements appears which
often shows a parallel orientation (Runnström, 1955). The cortex evidently exerts a certain orienting effect on elements that have a position
below the cortex in the strict sense. The birefringence of the cortex indicates that ordered fibrous elements may also be present here. The ground
substance of the cortex may have a similar structure to that suggested
above for the vitelline membrane.
The cortex of the mature unfertilized egg acquires a special character
by the presence of the so-called cortical granules. In view of their complicated and composite nature, it is suggested here that they should be
designated as "cortical particles." They are arranged in a single layer,
and their outer limits are very close to the plasma membrane. They have
a diameter that for one single species is rather constant. When several
species are compared, values between 0.7 and 0.9 μ are found (Afzelius,
1956, Table I). The number present in the surface of a mature unfertilized egg of Psammechinus
miliaris is around 120 per 100 μ
2
. This
agrees well with the data given for Strongylocentrotus
pulcherrimus,
whereas in Clypeaster
japonicus, the number was 60 per 100 μ
2
(see
Endo, 1952).
Β. Structure and Differentiation of the Cortical Particles
1. The Cortical Particles of the Mature
Egg
A more intimate knowledge of the structure of the cortical particles
could be obtained only after the electron microscope became available
for their study. The pioneer work was carried out by McCulloch (1952),
Lansing et al. (1952), Cheney and Lansing (1955), and Afzelius (1956).
The last-mentioned author gave the most comprehensive data covering
a number of different species. The earlier data have been supplemented
by the work of Rothschild (1958), Motomura (1960), Wolpert and
Mercer (1961), and, particularly, by that of Endo (1961a) pertaining to
the cortical particles of the irregular sea urchin, Clypeaster
japonicus.
The last-mentioned studies definitely settled some questions concerning
the presumptive value of the components of the cortical particles.
Osmium tetroxide dissolved in sea water or in various buffers was
upon maturation, changes also take place in the jelly coat. After maturation the jelly becomes more sensitive to a depolymerizing effect of
added spermatozoa (see Runnström, 1964). The relation between these
phenomena is, however, not clear.
In the living mature egg a certain tangential orientation of fibrillar
material is observed even below the cortex proper. When the sea water
surrounding the eggs gradually becomes hypertonic because of evaporation, a negative birefringence of the fibrillar elements appears which
often shows a parallel orientation (Runnström, 1955). The cortex evidently exerts a certain orienting effect on elements that have a position
below the cortex in the strict sense. The birefringence of the cortex indicates that ordered fibrous elements may also be present here. The ground
substance of the cortex may have a similar structure to that suggested
above for the vitelline membrane.
The cortex of the mature unfertilized egg acquires a special character
by the presence of the so-called cortical granules. In view of their complicated and composite nature, it is suggested here that they should be
designated as "cortical particles." They are arranged in a single layer,
and their outer limits are very close to the plasma membrane. They have
a diameter that for one single species is rather constant. When several
species are compared, values between 0.7 and 0.9 μ are found (Afzelius,
1956, Table I). The number present in the surface of a mature unfertilized egg of Psammechinus
miliaris is around 120 per 100 μ
2
. This
agrees well with the data given for Strongylocentrotus
pulcherrimus,
whereas in Clypeaster
japonicus, the number was 60 per 100 μ
2
(see
Endo, 1952).
Β. Structure and Differentiation of the Cortical Particles
1. The Cortical Particles of the Mature
Egg
A more intimate knowledge of the structure of the cortical particles
could be obtained only after the electron microscope became available
for their study. The pioneer work was carried out by McCulloch (1952),
Lansing et al. (1952), Cheney and Lansing (1955), and Afzelius (1956).
The last-mentioned author gave the most comprehensive data covering
a number of different species. The earlier data have been supplemented
by the work of Rothschild (1958), Motomura (1960), Wolpert and
Mercer (1961), and, particularly, by that of Endo (1961a) pertaining to
the cortical particles of the irregular sea urchin, Clypeaster
japonicus.
The last-mentioned studies definitely settled some questions concerning
the presumptive value of the components of the cortical particles.
Osmium tetroxide dissolved in sea water or in various buffers was