290
J O H N R U N N S T R Ö M
FIG. 27. Opening of cortical particle in Psammechinus miliaris. Left horizontal
arrow, released, shrinking lamella; vertical arrow, expanded extralamellar bodies
attached to the bottom of the cortical hollow; right horizontal arrow, lamella in
the stage of incorporation into the fertilization membrane. X 50,000. (Afzelius.)
The extralamellar bodies (vertical arrow) seen in Fig. 27 have a
configuration t h a t is typical of the stage in which the cortical particle
opens up and also of a certain period after the opening. The lamellar
bodies have expanded to a sheet covering the inner side of the membrane
of the particle and connected with this membrane by numerous threadlike projections. Not only the lamella but also the extralamellar bodies
are thus influenced by the changed conditions prevailing in the cortical
particles initiating ther opening. The presence of connections with the
particle membrane corresponds, however, to a state t h a t was established
before the opening (Sections Ι,Β,Ι and 2 ) .
The extrusion of the interior matrix from the lamella continues when
the lamella has passed through the opened stoma of the cortical particle
into the perivitelline space. The coiled filaments can no longer be perceived within the condensed and flattened lamella, but there is a certain
substructure which indicates t h a t the change mainly involves a dehydration and a denser packing of the same elements t h a t were present in
the lamella of the intact cortical particle. Single vacuoles m a y also
coalesce into one somewhat larger vacuole. The site of this larger vacuole
seems to indicate the pole of attachment to the vitelline membrane. This
was particularly observed in Echinus
esculentus
and
Paracentrotus
lividus.
Runnström (1958) followed the attachment of the lamella and its
J O H N R U N N S T R Ö M
FIG. 27. Opening of cortical particle in Psammechinus miliaris. Left horizontal
arrow, released, shrinking lamella; vertical arrow, expanded extralamellar bodies
attached to the bottom of the cortical hollow; right horizontal arrow, lamella in
the stage of incorporation into the fertilization membrane. X 50,000. (Afzelius.)
The extralamellar bodies (vertical arrow) seen in Fig. 27 have a
configuration t h a t is typical of the stage in which the cortical particle
opens up and also of a certain period after the opening. The lamellar
bodies have expanded to a sheet covering the inner side of the membrane
of the particle and connected with this membrane by numerous threadlike projections. Not only the lamella but also the extralamellar bodies
are thus influenced by the changed conditions prevailing in the cortical
particles initiating ther opening. The presence of connections with the
particle membrane corresponds, however, to a state t h a t was established
before the opening (Sections Ι,Β,Ι and 2 ) .
The extrusion of the interior matrix from the lamella continues when
the lamella has passed through the opened stoma of the cortical particle
into the perivitelline space. The coiled filaments can no longer be perceived within the condensed and flattened lamella, but there is a certain
substructure which indicates t h a t the change mainly involves a dehydration and a denser packing of the same elements t h a t were present in
the lamella of the intact cortical particle. Single vacuoles m a y also
coalesce into one somewhat larger vacuole. The site of this larger vacuole
seems to indicate the pole of attachment to the vitelline membrane. This
was particularly observed in Echinus
esculentus
and
Paracentrotus
lividus.
Runnström (1958) followed the attachment of the lamella and its