VITELLINE MEMBRANE AND CORTICAL PARTICLES 291
further changes step by step by immersing the eggs of Paracentrotus
at
different times (10-300 sec) after insemination in 1.75 X 10"
4 M porphyrexid, which stops the incorporation (timed blocking). The same timed
blocking was obtained by immersion in 3.2 χ 10~
4 M Cu
2 +
. The retardation in the pivotlike lamella is not measurable, but an increasing
retardation evolves in step with the flattening of the lamella against the
vitelline membrane. A lamella in this stage is seen in Fig. 27 (right
horizontal arrow). This latter undergoes, probably, certain changes
which may involve polymerization processes. The designation "lamella"
introduced by Endo (1961a), applies particularly to this stage of
flattening.
The flattening occurs by a sort of sliding process. The borrowing of
this designation from muscle physiology (Huxley, 1953) is not unintentional. The process must be due to the establishment of new linkages
which are reversible in the muscle but are irreversible in the case of
the formation of the fertilization membrane. When the flattening process
has been achieved, the retardation at the edge of the fertilization membrane has attained a value of ca. 12 ηΐμ, a value that is surprisingly
constant in eggs (see Runnström, 1964) despite the ill-defined depth
of the biréfringent material at the edge of a curved surface. The measurements of retardation allow, however, the observation of changes which
reflect changes in internal structure. The delayed lamellae are converted
into rods or plates present in the perivitelline space (Runnström, 1948;
Endo, 1952). This conversion to rods and plates which in
Psammechinus
or Paracentrotus
occurs ca. 5 min after insemination involves a further
dehydration of the lamella; in connection with this, a birefringence
appears which has the same character and retardation as that of the
fertilization membrane. Before this stage the delayed lamella was in
Brownian movement; after the conversion this movement stops.
After the union of the lamella with the vitelline membrane is accomplished, the fertilization membrane attains a thickness of 500 Â. This
value was first given by Mitchison (1956) using interference microscopy.
His result was confirmed by measurements on electron micrographs
carried out by Afzelius (1956). Even when different species are compared, a remarkable constancy of the thickness of the fertilization
membrane is found. The extralamellar bodies develop into the boundary
of the hyaline layer. This occurs by a gradual rupture of the connections between the extralamellar sheet (Fig. 27) and the membrane of
the "cortical hollow," as the opened cortical particles may be called,
after extrusion of the lamellae. Finally the sheet remains attached only
to the tops of the villi and thus constitutes the above-mentioned
boundary.
further changes step by step by immersing the eggs of Paracentrotus
at
different times (10-300 sec) after insemination in 1.75 X 10"
4 M porphyrexid, which stops the incorporation (timed blocking). The same timed
blocking was obtained by immersion in 3.2 χ 10~
4 M Cu
2 +
. The retardation in the pivotlike lamella is not measurable, but an increasing
retardation evolves in step with the flattening of the lamella against the
vitelline membrane. A lamella in this stage is seen in Fig. 27 (right
horizontal arrow). This latter undergoes, probably, certain changes
which may involve polymerization processes. The designation "lamella"
introduced by Endo (1961a), applies particularly to this stage of
flattening.
The flattening occurs by a sort of sliding process. The borrowing of
this designation from muscle physiology (Huxley, 1953) is not unintentional. The process must be due to the establishment of new linkages
which are reversible in the muscle but are irreversible in the case of
the formation of the fertilization membrane. When the flattening process
has been achieved, the retardation at the edge of the fertilization membrane has attained a value of ca. 12 ηΐμ, a value that is surprisingly
constant in eggs (see Runnström, 1964) despite the ill-defined depth
of the biréfringent material at the edge of a curved surface. The measurements of retardation allow, however, the observation of changes which
reflect changes in internal structure. The delayed lamellae are converted
into rods or plates present in the perivitelline space (Runnström, 1948;
Endo, 1952). This conversion to rods and plates which in
Psammechinus
or Paracentrotus
occurs ca. 5 min after insemination involves a further
dehydration of the lamella; in connection with this, a birefringence
appears which has the same character and retardation as that of the
fertilization membrane. Before this stage the delayed lamella was in
Brownian movement; after the conversion this movement stops.
After the union of the lamella with the vitelline membrane is accomplished, the fertilization membrane attains a thickness of 500 Â. This
value was first given by Mitchison (1956) using interference microscopy.
His result was confirmed by measurements on electron micrographs
carried out by Afzelius (1956). Even when different species are compared, a remarkable constancy of the thickness of the fertilization
membrane is found. The extralamellar bodies develop into the boundary
of the hyaline layer. This occurs by a gradual rupture of the connections between the extralamellar sheet (Fig. 27) and the membrane of
the "cortical hollow," as the opened cortical particles may be called,
after extrusion of the lamellae. Finally the sheet remains attached only
to the tops of the villi and thus constitutes the above-mentioned
boundary.