VITELLINE MEMBRANE AND CORTICAL PARTICLES 241
The configuration of the cortical particles will finally be discussed
for some representatives of the genus Strongylocentrotus
belonging to
the family Toxopneustidae. The type found is different from those previously referred to, but certain traits are common to the three species for
which data are available. Afzelius (1956, Fig. 3) has published a micrograph in which the structure of the lamella can be studied in detail. It
has the form of a convex shield that has an elliptic outline (largest diameter ca. 0.98 μ, smallest ca. 0.8 μ). Parallel to the margin, a number
of rather closely cross-linked concentric filaments are observed. Their
width is about 135 Â, and the distance between the cross-links is approximately the same. The center of the shield (Fig. 13, horizontal
arrow) corresponds to the top pole of the cortical particle. Below (proximally of) the shield, a much less organized mass of rather dense substance (vertical arrows) is present, which is composed of fibers and
granules. This fibrous granular mass evidently corresponds to a nonsubdivided extralamellar body that on rather a broad frontier is attached
on one side to the shield, on the other to the membrane of the cortical
particle.
Figure 14 is a section through a part of the cortex of an unfertilized
egg of Strongylocentrotus
pwrpuratus.
The same main portions are
found as in Strongylocentrotus
droebachiensis.
Most proximally, the fibrous granular extralamella is seen (lower arrow) attached to the membrane. In the next region (middle arrow) the fibrous granular structure
is denser. This region was not as pronounced in S. droebachiensis.
It
probably corresponds to the basal lamellar region from which the coiled
filaments originate. The impression gained is that the basal region contains the material that serves as building material and as organizer of
the distal framework (upper arrow) of the lamella. This part of the cortical particle is more dispersed than in S. droebachiensis.
The matrix
occupies, both outside and inside the lamella, more space in S. purpuratus
than in S. droebachiensis.
The distal lamella in the former species resembles the lamella in the cortical particles of Paracentrotus.
The thin
connections are, however, less numerous in S. purpuratus. It seems from
the electron micrograph (Fig. 14) that these connections are helices with
a period of about 200 Â. The cortical particles of S. purpuratus thus far
give the clearest picture of the subdivision of these organoids.
The cortical particles of Strongylocentrotus
(Hemicentrotus)
pulcherrimus have been described by Motomura (1960). The lamella is elongated
in one direction and seems to have a shieldlike structure similar to that
found in S. droebachiensis,
although the cross-linking is not as pronounced. Motomura (loc. ait.) mentions that from five to nine granular
inclusions are present near the peripheral region. These may represent
The configuration of the cortical particles will finally be discussed
for some representatives of the genus Strongylocentrotus
belonging to
the family Toxopneustidae. The type found is different from those previously referred to, but certain traits are common to the three species for
which data are available. Afzelius (1956, Fig. 3) has published a micrograph in which the structure of the lamella can be studied in detail. It
has the form of a convex shield that has an elliptic outline (largest diameter ca. 0.98 μ, smallest ca. 0.8 μ). Parallel to the margin, a number
of rather closely cross-linked concentric filaments are observed. Their
width is about 135 Â, and the distance between the cross-links is approximately the same. The center of the shield (Fig. 13, horizontal
arrow) corresponds to the top pole of the cortical particle. Below (proximally of) the shield, a much less organized mass of rather dense substance (vertical arrows) is present, which is composed of fibers and
granules. This fibrous granular mass evidently corresponds to a nonsubdivided extralamellar body that on rather a broad frontier is attached
on one side to the shield, on the other to the membrane of the cortical
particle.
Figure 14 is a section through a part of the cortex of an unfertilized
egg of Strongylocentrotus
pwrpuratus.
The same main portions are
found as in Strongylocentrotus
droebachiensis.
Most proximally, the fibrous granular extralamella is seen (lower arrow) attached to the membrane. In the next region (middle arrow) the fibrous granular structure
is denser. This region was not as pronounced in S. droebachiensis.
It
probably corresponds to the basal lamellar region from which the coiled
filaments originate. The impression gained is that the basal region contains the material that serves as building material and as organizer of
the distal framework (upper arrow) of the lamella. This part of the cortical particle is more dispersed than in S. droebachiensis.
The matrix
occupies, both outside and inside the lamella, more space in S. purpuratus
than in S. droebachiensis.
The distal lamella in the former species resembles the lamella in the cortical particles of Paracentrotus.
The thin
connections are, however, less numerous in S. purpuratus. It seems from
the electron micrograph (Fig. 14) that these connections are helices with
a period of about 200 Â. The cortical particles of S. purpuratus thus far
give the clearest picture of the subdivision of these organoids.
The cortical particles of Strongylocentrotus
(Hemicentrotus)
pulcherrimus have been described by Motomura (1960). The lamella is elongated
in one direction and seems to have a shieldlike structure similar to that
found in S. droebachiensis,
although the cross-linking is not as pronounced. Motomura (loc. ait.) mentions that from five to nine granular
inclusions are present near the peripheral region. These may represent