140
SAUL WISCHNITZER
At the time when the villi are maximally developed (oocyte diameter of
~750 μ), the zona pellucida is perforated by the downward extending
macrovilli. These are about 0.2 μ in diameter and are now sunk into short
tubelike inpocketings of the plasmalemma which push downward into the
peripheral oocyte cytoplasm. There the macrovilli presumably are anchored
by their desmosomes (Wartenberg, 1962; Hope et al., 1963). The microvilli
Very early oocyte ~ 100/x
Early oocyte ~ 300/1
Maturing oocyte ~ 500/i
Maturing oocyte ~750/i
Ovulated egg ~ 1600/i.
Fertilized egg ~ \&00μ
FIG. 6. A diagrammatic representation of the development of the acellular zona
pellucida and formation of the villi at the periphery of the oocyte. SE, surface
epithelium; T, theca; FE, follicular epithelium; p, plasmalemma; PC, peripheral
cytoplasm; VM, vitelline membrane; FM, fertilization membrane; PS, perivitelline space; PC, peripheral cytoplasm; Ma, macrovilli; Mi, microvilli; ZP,
zona pellucida.
at this developmental stage are about 0.1 μ in diameter and project up in
urodeles to the level of the interface between the homogeneous layer and
the zona radiata. In anurans, this interface would be present at about
three-fifths of the way up through the zona pellucida (or radiata). A threedimensional representation of this developmental stage is shown in Fig. 7.
During later developmental stages when the oocyte has fully matured
(diameter of ^1600 μ), the villi begin to regress and withdraw from the
zona pellucida (Wartenberg and Schmidt, 1961; Hope et al., 1963). When
SAUL WISCHNITZER
At the time when the villi are maximally developed (oocyte diameter of
~750 μ), the zona pellucida is perforated by the downward extending
macrovilli. These are about 0.2 μ in diameter and are now sunk into short
tubelike inpocketings of the plasmalemma which push downward into the
peripheral oocyte cytoplasm. There the macrovilli presumably are anchored
by their desmosomes (Wartenberg, 1962; Hope et al., 1963). The microvilli
Very early oocyte ~ 100/x
Early oocyte ~ 300/1
Maturing oocyte ~ 500/i
Maturing oocyte ~750/i
Ovulated egg ~ 1600/i.
Fertilized egg ~ \&00μ
FIG. 6. A diagrammatic representation of the development of the acellular zona
pellucida and formation of the villi at the periphery of the oocyte. SE, surface
epithelium; T, theca; FE, follicular epithelium; p, plasmalemma; PC, peripheral
cytoplasm; VM, vitelline membrane; FM, fertilization membrane; PS, perivitelline space; PC, peripheral cytoplasm; Ma, macrovilli; Mi, microvilli; ZP,
zona pellucida.
at this developmental stage are about 0.1 μ in diameter and project up in
urodeles to the level of the interface between the homogeneous layer and
the zona radiata. In anurans, this interface would be present at about
three-fifths of the way up through the zona pellucida (or radiata). A threedimensional representation of this developmental stage is shown in Fig. 7.
During later developmental stages when the oocyte has fully matured
(diameter of ^1600 μ), the villi begin to regress and withdraw from the
zona pellucida (Wartenberg and Schmidt, 1961; Hope et al., 1963). When