VITELLINE MEMBRANE AND CORTICAL PARTICLES 289
This section refers to phenomena that perhaps do not strictly belong
to the subject of this article. They demonstrate, however, that the
cortical changes are necessary steps also for the subsequent interior
changes. It seems that even the removal of the inhibitor acting on the
centrosome is dependent on a process in the cortex. A drastic demonstration of the importance of the cortex in fertilization was provided by the
experiment of Hiramoto (1962) in which he injected spermatozoa into
the interior of unfertilized Paracentrotus
or Psammechinus
eggs. The
injected spermatozoa did not activate the eggs but remained intact and
even motile within the endoplasm.
III. Structural Changes after the Opening of the Cortical Particles
A. Conversion of the Lamellae and Extralamellar Bodies into
Components of the Fertilization Membrane and the Hyaline Layer
When the lamella joins the vitelline membrane, it has at first
a pivotlike appearance, as in Fig. 21 of Runnström et al. (1959) in the
case of Echinus esculentus and Fig. 6 of Endo (1961a) in the case of
Clypeaster
japonicus.
The study of the cortical particles which are
still closed in unfertilized eggs has shown that there are threadlike
connections between the lamella and the extralamellar bodies and often
also between the lamella and the membrane, as is particularly clear in
Brissopsis
(Section Ι,Β,Ι). These connections must be broken up. The
same problem has to be faced here as in the separation of the vitelline
membrane from the egg surface.
Figure 27 is an electron micrograph of an egg of Psammechinus
miliaris
in which the fertilization membrane is under elevation. A cortical particle
is seen in the so-called transition zone (Wolpert and Mercer, 1961).
Both the lamella and the extralamellar bodies are present, but they
have no perceptible connection with each other. The lamella (left
horizontal arrow) has evidently contracted, and some of the interior
matrix has been pressed out. It seems probable that the particle shown
is just in the phase of opening. According to unpublished cinematographic
material of Dr. Β. E. Hagström (1964), one of the first changes to be
observed after effective attachment of a spermatozoon is a pronounced
Brownian movement within the cortical particles in an area around the
attached spermatozoon. This movement starts at a time when the elevation of a fertilization membrane is not yet perceptible. The Brownian
movement must reflect the breakup of the connections between lamella
and extralamellar bodies. The Brownian movement must be ascribed
to the lamella, since the extralamellar bodies are still attached to the
membrane of the particle.
This section refers to phenomena that perhaps do not strictly belong
to the subject of this article. They demonstrate, however, that the
cortical changes are necessary steps also for the subsequent interior
changes. It seems that even the removal of the inhibitor acting on the
centrosome is dependent on a process in the cortex. A drastic demonstration of the importance of the cortex in fertilization was provided by the
experiment of Hiramoto (1962) in which he injected spermatozoa into
the interior of unfertilized Paracentrotus
or Psammechinus
eggs. The
injected spermatozoa did not activate the eggs but remained intact and
even motile within the endoplasm.
III. Structural Changes after the Opening of the Cortical Particles
A. Conversion of the Lamellae and Extralamellar Bodies into
Components of the Fertilization Membrane and the Hyaline Layer
When the lamella joins the vitelline membrane, it has at first
a pivotlike appearance, as in Fig. 21 of Runnström et al. (1959) in the
case of Echinus esculentus and Fig. 6 of Endo (1961a) in the case of
Clypeaster
japonicus.
The study of the cortical particles which are
still closed in unfertilized eggs has shown that there are threadlike
connections between the lamella and the extralamellar bodies and often
also between the lamella and the membrane, as is particularly clear in
Brissopsis
(Section Ι,Β,Ι). These connections must be broken up. The
same problem has to be faced here as in the separation of the vitelline
membrane from the egg surface.
Figure 27 is an electron micrograph of an egg of Psammechinus
miliaris
in which the fertilization membrane is under elevation. A cortical particle
is seen in the so-called transition zone (Wolpert and Mercer, 1961).
Both the lamella and the extralamellar bodies are present, but they
have no perceptible connection with each other. The lamella (left
horizontal arrow) has evidently contracted, and some of the interior
matrix has been pressed out. It seems probable that the particle shown
is just in the phase of opening. According to unpublished cinematographic
material of Dr. Β. E. Hagström (1964), one of the first changes to be
observed after effective attachment of a spermatozoon is a pronounced
Brownian movement within the cortical particles in an area around the
attached spermatozoon. This movement starts at a time when the elevation of a fertilization membrane is not yet perceptible. The Brownian
movement must reflect the breakup of the connections between lamella
and extralamellar bodies. The Brownian movement must be ascribed
to the lamella, since the extralamellar bodies are still attached to the
membrane of the particle.