142
SAUL WISCHNITZER
The deposition of matrix material between the follicle epithelium and
oocyte is characteristic of all developing vertebrate forms. In amphibians,
this deposition is more complex than in other forms. This is due to the fact
that only a single type of ground substance is present in anurans, whereas
two matrices are present in urodeles. In the latter organisms, the matrix
materials are present in two sharply demarcated layers, each having its
own characteristics. The outer one-fifth of the zona pellucida, constituting
a homogeneous layer, consists of a loosely granular material. This layer is
perforated only by the macrovilli. The zona radiata, which occupies the
inner four-fifths, consists of dense granular material that is perforated by
numerous microvilli as well as macrovilli.
In all amphibians, Wartenberg (1962) found that the ground substance
of the zona pellucida could be differentiated histochemically into two
layers. Thus, the homogeneous layer in urodeles and the outer portion of
the zona pellucida in anurans both give an especially strong positive periodic
Schiff reaction as compared to the larger inner part of the zona pellucida.
For more than a half century, the origin of the matrix material comprising
the zona pellucida has been disputed. Three possible sites of synthesis were
postulated for vertebrate ova. In amphibians, Waldeyer (1870), and
somewhat later, Iwakawa (1882) and Schultz (1887) suggested that the
acellular layers were derived from the egg. King (1908), on the other hand,
took a diametrically opposite view and claimed that the follicle cells produce
the ground substance. Waldeyer (1906) revised his original opinion and
arrived at the intermediate position that the "vitelline membrane" (homogeneous layer, see Wischnitzer, 1963a) was produced by the follicle cells,
whereas the zona radiata was a derivative of the developing egg.
Observations based on electron-microscope and histochemical studies, as
presented above, support the contention that the zona pellucida is a product
of the activity of both the developing oocyte and its follicular epithelium.
This conclusion, however, can be supported only by indirect evidence, which
consists of the following three points.
1. It is more plausible to explain this observation on the basis of a dual
site of origin rather than a single site. In the latter case, deposition of
one layer after the other would have to take place.
2. The two layers are sharply and evenly demarcated from each other
in urodeles. This suggests that the formation of matrix material in
each layer is well regulated, occurs simultaneously around the circumference of the ovum, and takes place at two sites.
3. Even in cases, such as anurans, where two morphologically distinct
layers are not evident with the electron microscope, two strata can
be identified histochemically.
The intracellular organelles in the ovum and follicle cells responsible
for the formation of the ground substance are unknown. Merker (1961)
SAUL WISCHNITZER
The deposition of matrix material between the follicle epithelium and
oocyte is characteristic of all developing vertebrate forms. In amphibians,
this deposition is more complex than in other forms. This is due to the fact
that only a single type of ground substance is present in anurans, whereas
two matrices are present in urodeles. In the latter organisms, the matrix
materials are present in two sharply demarcated layers, each having its
own characteristics. The outer one-fifth of the zona pellucida, constituting
a homogeneous layer, consists of a loosely granular material. This layer is
perforated only by the macrovilli. The zona radiata, which occupies the
inner four-fifths, consists of dense granular material that is perforated by
numerous microvilli as well as macrovilli.
In all amphibians, Wartenberg (1962) found that the ground substance
of the zona pellucida could be differentiated histochemically into two
layers. Thus, the homogeneous layer in urodeles and the outer portion of
the zona pellucida in anurans both give an especially strong positive periodic
Schiff reaction as compared to the larger inner part of the zona pellucida.
For more than a half century, the origin of the matrix material comprising
the zona pellucida has been disputed. Three possible sites of synthesis were
postulated for vertebrate ova. In amphibians, Waldeyer (1870), and
somewhat later, Iwakawa (1882) and Schultz (1887) suggested that the
acellular layers were derived from the egg. King (1908), on the other hand,
took a diametrically opposite view and claimed that the follicle cells produce
the ground substance. Waldeyer (1906) revised his original opinion and
arrived at the intermediate position that the "vitelline membrane" (homogeneous layer, see Wischnitzer, 1963a) was produced by the follicle cells,
whereas the zona radiata was a derivative of the developing egg.
Observations based on electron-microscope and histochemical studies, as
presented above, support the contention that the zona pellucida is a product
of the activity of both the developing oocyte and its follicular epithelium.
This conclusion, however, can be supported only by indirect evidence, which
consists of the following three points.
1. It is more plausible to explain this observation on the basis of a dual
site of origin rather than a single site. In the latter case, deposition of
one layer after the other would have to take place.
2. The two layers are sharply and evenly demarcated from each other
in urodeles. This suggests that the formation of matrix material in
each layer is well regulated, occurs simultaneously around the circumference of the ovum, and takes place at two sites.
3. Even in cases, such as anurans, where two morphologically distinct
layers are not evident with the electron microscope, two strata can
be identified histochemically.
The intracellular organelles in the ovum and follicle cells responsible
for the formation of the ground substance are unknown. Merker (1961)