VITELLINE MEMBRANE AND CORTICAL PARTICLES
239
FIG. 12. A and B: Two cortical particles of Echinus esculentus. Abbreviations: 1,
lamellar filaments; st, stalk or basal region of the lamella; el, extralamellar bodies.
X 100,000. (Cf. Afzelius, 1956, Fig. 2.)
The genus Psammechinus
is closely related to Paracentrotus.
Afzelius
(1956) described the cortical particles in the ripe eggs of
Psammechinus
miliaris; they resemble in detail those of Paracentrotus,
as this writer
found in his own studies. The basal region of the lamella is often larger
and more distinctly limited than in Paracentrotus.
The structure of the
slender coiled filaments seems to be less ordered than in
Paracentrotus,
due to a less regular development of the vacuoles. These vacuoles may
contribute more effectively in Paracentrotus
than in Psammechinus
to
the structural stability of the filaments. Cross sections of the filaments
had a diameter of about 500 Â. The number of the extralamellar bodies
seemed often to be only two, but they were correspondingly larger in
size. They often have a granular substructure.
The cortical particles of Echinus esculentus have a configuration similar to that of the previously described cortical particles in
Paracentrotus
and Psammechinus.
Nevertheless, there is a distinct difference indicating
that the genetical background is rather different in Echinus, on one side,
and in Paracentrotus
and Psammechinus,
on the other. In the former
species the structure of the cortical particles seems more compact, due