144
SAUL WISCHNITZER
of an array of rods or granules. Others, however, correctly interpreted them
as minute canals containing protoplasmic processes (see reviews by Thing,
1918; Fischer, 1932).
The formation of the macrovilli is more complex. They apparently result
from the active participation of several factors. The observation that they
are formed at sites where desmosomes are present (Wartenberg, 1962;
Hope et al., 1963) suggests that their formation may be a passive event.
Thus, at the outset, a macro villus may be considered as the broad depression located at a site of desmosomal attachment, which is present between
the groups of microvilli associated with the two adjacent interdesmosomal
segments. By the continued deposition of the ground substance, such a
club-shaped depression is elongated into a cylindrical unit. By retraction of
the plasmalemma, the apex of the macrovillus becomes embedded into a
tubelike depression in the periphery of the oocyte. Presumably, macrovilli
are rapidly withdrawn after the desomosomes are broken down as they are
no longer evident at ovulation, at which time remnants of the short microvilli are still present. In mammals, the presence of desmosomes binding the
follicle (granulosa) cell projections with the plasmalemma was observed
by Franchi (1960) in the rat and by Wartenberg and Stegner (1960) in
human ova.
Functionally, the zona pellucida appears to provide a means for exchange
of material between the developing egg and its environment. The matrix
material, then, would serve primarily as a morphological entity that
separates the egg from the closely adherent follicular epithelium. As a
result, structural processes from both surfaces can be formed. These
processes would then insure maintenance of the nutritive functions essential
for the growth of the egg at a critical stage in its development. Following
ovulation, at least in mammals, several functions have been ascribed to the
zona pellucida. These include the restriction of polyspermy (Braden et al.,
1954), maintenance of the normal cleavage pattern, and prevention of egg
fusion (Mintz, 1962).
Hope et al. (1963) postulated an additional possible site of physiological
exchange. This is by means of the intercellular spaces that exist between
the follicle cells which appear to be continuous with the homogeneous layer
of the zona pellucida at one end and the theca at the other. They have
therefore suggested this as a potential route for material to pass from blood
vessels of the theca to the ovum.
Although it is possible, as Hope et al. (1963) suggested, that there is a
relative direct communication between the developing oocyte and circulatory system of the organism in localized regions, the overwhelming surface area of the oocyte is in contact only with its follicular epithelium. The
SAUL WISCHNITZER
of an array of rods or granules. Others, however, correctly interpreted them
as minute canals containing protoplasmic processes (see reviews by Thing,
1918; Fischer, 1932).
The formation of the macrovilli is more complex. They apparently result
from the active participation of several factors. The observation that they
are formed at sites where desmosomes are present (Wartenberg, 1962;
Hope et al., 1963) suggests that their formation may be a passive event.
Thus, at the outset, a macro villus may be considered as the broad depression located at a site of desmosomal attachment, which is present between
the groups of microvilli associated with the two adjacent interdesmosomal
segments. By the continued deposition of the ground substance, such a
club-shaped depression is elongated into a cylindrical unit. By retraction of
the plasmalemma, the apex of the macrovillus becomes embedded into a
tubelike depression in the periphery of the oocyte. Presumably, macrovilli
are rapidly withdrawn after the desomosomes are broken down as they are
no longer evident at ovulation, at which time remnants of the short microvilli are still present. In mammals, the presence of desmosomes binding the
follicle (granulosa) cell projections with the plasmalemma was observed
by Franchi (1960) in the rat and by Wartenberg and Stegner (1960) in
human ova.
Functionally, the zona pellucida appears to provide a means for exchange
of material between the developing egg and its environment. The matrix
material, then, would serve primarily as a morphological entity that
separates the egg from the closely adherent follicular epithelium. As a
result, structural processes from both surfaces can be formed. These
processes would then insure maintenance of the nutritive functions essential
for the growth of the egg at a critical stage in its development. Following
ovulation, at least in mammals, several functions have been ascribed to the
zona pellucida. These include the restriction of polyspermy (Braden et al.,
1954), maintenance of the normal cleavage pattern, and prevention of egg
fusion (Mintz, 1962).
Hope et al. (1963) postulated an additional possible site of physiological
exchange. This is by means of the intercellular spaces that exist between
the follicle cells which appear to be continuous with the homogeneous layer
of the zona pellucida at one end and the theca at the other. They have
therefore suggested this as a potential route for material to pass from blood
vessels of the theca to the ovum.
Although it is possible, as Hope et al. (1963) suggested, that there is a
relative direct communication between the developing oocyte and circulatory system of the organism in localized regions, the overwhelming surface area of the oocyte is in contact only with its follicular epithelium. The