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SAUL WISCHNITZER
also known as the inner layer of the zona radiata (Wartenberg, 1962).
In anurans, where only one acellular stratum is present, the term zona
radiata is synonymous with zona pellucida.
Zona pellucida. A term used to describe the entire region between
the follicular epithelium and unovulated egg. This zone in anurans
thus encompasses both the homogeneous layer and adjacent zona
radiata. The use of the term zona pellucida in the case of a nonmammalian form is in keeping with its early usage by Eimer (1872) and Thing
(1918). This definition is also consistent with the current usage of
the term by Wartenberg (1962), Zahnd and Porte (1962), Hope et al.
(1963), and Wischnitzer (1964b).
Vitelline membrane. This term will be restricted to the layer enveloping the egg after ovulation and until fertilization. This stratum is
thus a derivative, in part or in whole, of the zona pellucida.
Fertilization membrane. The name given to the vitelline membrane
after fertilization takes place.
Plasmalemma. The plasma membrane enveloping the developing oocyte.
C. Formation of the Egg Envelopes
The amphibian egg becomes enveloped by its cellular and acellular
layers during the prophase of the first meiotic division (Fig. 1). The
meiotic process is initiated by a marked increase in mitoses of the primordial
germ cells and results in the formation of a large number of oogonia. These
cells lie within a connective tissue stroma that is sandwiched between the
peritoneum and inner ovarian wall. The oogonia are characteristically
large, pale, and almost spherical shaped. They are found in groups known
as germ patches or egg cell nests. Fibroblasts, recognized by their darkstaining nuclei, are found at the periphery of the clusters of cells. After
transformation of the oogonia to oocytes, the latter gradually become
separated from each other, and individual developing oocytes come to be
surrounded by fibroblasts. The fibroblasts become specialized, and in time
will become organized into the follicle cell epithelium. The oocyte passes
through the early prophase stages, and at the diplotene stage active synthesis of cytoplasmic inclusions, especially yolk formation, is initiated. This
results in a rapid growth of the oocyte and its inward protrusion against,
and gradual envelopment by, the inner ovarian epithelium. In time, the
oocyte becomes completely surrounded by this layer which now forms the
surface epithelium. The oocyte remains in contact with the peritoneal
layer only at the site where rupture of the wall will take place at the time
of ovulation. Beneath the surface epithelium lies the theca, the connective
tissue layer that represents the stratification of the original material
containing the oocyte. The innermost cellular layer becomes highly organ-
SAUL WISCHNITZER
also known as the inner layer of the zona radiata (Wartenberg, 1962).
In anurans, where only one acellular stratum is present, the term zona
radiata is synonymous with zona pellucida.
Zona pellucida. A term used to describe the entire region between
the follicular epithelium and unovulated egg. This zone in anurans
thus encompasses both the homogeneous layer and adjacent zona
radiata. The use of the term zona pellucida in the case of a nonmammalian form is in keeping with its early usage by Eimer (1872) and Thing
(1918). This definition is also consistent with the current usage of
the term by Wartenberg (1962), Zahnd and Porte (1962), Hope et al.
(1963), and Wischnitzer (1964b).
Vitelline membrane. This term will be restricted to the layer enveloping the egg after ovulation and until fertilization. This stratum is
thus a derivative, in part or in whole, of the zona pellucida.
Fertilization membrane. The name given to the vitelline membrane
after fertilization takes place.
Plasmalemma. The plasma membrane enveloping the developing oocyte.
C. Formation of the Egg Envelopes
The amphibian egg becomes enveloped by its cellular and acellular
layers during the prophase of the first meiotic division (Fig. 1). The
meiotic process is initiated by a marked increase in mitoses of the primordial
germ cells and results in the formation of a large number of oogonia. These
cells lie within a connective tissue stroma that is sandwiched between the
peritoneum and inner ovarian wall. The oogonia are characteristically
large, pale, and almost spherical shaped. They are found in groups known
as germ patches or egg cell nests. Fibroblasts, recognized by their darkstaining nuclei, are found at the periphery of the clusters of cells. After
transformation of the oogonia to oocytes, the latter gradually become
separated from each other, and individual developing oocytes come to be
surrounded by fibroblasts. The fibroblasts become specialized, and in time
will become organized into the follicle cell epithelium. The oocyte passes
through the early prophase stages, and at the diplotene stage active synthesis of cytoplasmic inclusions, especially yolk formation, is initiated. This
results in a rapid growth of the oocyte and its inward protrusion against,
and gradual envelopment by, the inner ovarian epithelium. In time, the
oocyte becomes completely surrounded by this layer which now forms the
surface epithelium. The oocyte remains in contact with the peritoneal
layer only at the site where rupture of the wall will take place at the time
of ovulation. Beneath the surface epithelium lies the theca, the connective
tissue layer that represents the stratification of the original material
containing the oocyte. The innermost cellular layer becomes highly organ-