ULTRASTRUCTURE OF DEVELOPING AMPHIBIAN EGG 165
peripheral location, mitochondria from the yolk nucleus are then probably,
in part, responsible for the special characteristics of the peripheral cytoplasm (Rosenbaum, 1958). Thus, the yolk nucleus might be considered
as a unique cytoplasmic constituent, organized under nuclear influence
whose function is to facilitate the distribution of mitochondria so that they
can effectively carry out specialized functions.
Light-microscope studies of species in which a yolk nucleus is absent
indicate that the pattern of distribution of mitochondria is not radically
different from that where this organelle composite is present. In the latter
case, distribution of mitochondria also appears to involve their migration
from the nuclear region to the peripheral cytoplasm. Raven (1961) suggests
that at the very earliest stages, the mitochondria would be present as a mass
on one side of the nucleus. Then as Nath (1931) reported, he feels that the
mitochondria multiply to form a perinuclear mass. Subsequently, withdrawal of this material from the nucleus produces a perinuclear zone
devoid of mitochondria. Dispersal of the mitochondria then follows with
a uniform distribution taking place. The mitochondria appear as a peripheral layer, according to Nath (1931), only at late stages of development.
The aforementioned sequence of events have as yet not been confirmed
by electron microscopy. In the earliest oocytes studied, they are already
located at the periphery (Wartenberg, 1962; Wischnitzer, 1964b). Perhaps
the stages where perinuclear concentrations of mitochondria occur have
as yet been overlooked. The uniform distribution of mitochondria and their
concentration near the periphery have been verified by means of electron
microscopy.
The distribution of the Golgi complex during the course of oogenesis in
amphibians, summarized recently by Raven (1961), was studied by Hibbard
(1928), Nath (1931), and Saguchi (1932). They reported that in the earliest
stages of oogenesis the Golgi complex is found on one side of the cell nucleus.
The number of Golgi complexes is small at this time, but with the onset
of growth the number is increased. Dispersion of this organelle also commences until they are evenly distributed throughout the cytoplasm. Frequently they accumulate in the periphery of the oocyte. In the mature
egg, Golgi elements were found to be diminished in number and later even
absent. These light microscope findings are not in agreement with those
based on electron-microscope investigations which were cited earlier in
this paper. The discrepancy is possibly due to the identification of other
structures as Golgi material in the light-microscope investigations. Obviously, this problem needs to be reexamined.
It is not yet clear how multiplication of the Golgi complex takes place.
As a rule, it is assumed that it arises by fragmentation, constriction, or
division from existing organelles. Afzelius (1956), utilizing the electron
peripheral location, mitochondria from the yolk nucleus are then probably,
in part, responsible for the special characteristics of the peripheral cytoplasm (Rosenbaum, 1958). Thus, the yolk nucleus might be considered
as a unique cytoplasmic constituent, organized under nuclear influence
whose function is to facilitate the distribution of mitochondria so that they
can effectively carry out specialized functions.
Light-microscope studies of species in which a yolk nucleus is absent
indicate that the pattern of distribution of mitochondria is not radically
different from that where this organelle composite is present. In the latter
case, distribution of mitochondria also appears to involve their migration
from the nuclear region to the peripheral cytoplasm. Raven (1961) suggests
that at the very earliest stages, the mitochondria would be present as a mass
on one side of the nucleus. Then as Nath (1931) reported, he feels that the
mitochondria multiply to form a perinuclear mass. Subsequently, withdrawal of this material from the nucleus produces a perinuclear zone
devoid of mitochondria. Dispersal of the mitochondria then follows with
a uniform distribution taking place. The mitochondria appear as a peripheral layer, according to Nath (1931), only at late stages of development.
The aforementioned sequence of events have as yet not been confirmed
by electron microscopy. In the earliest oocytes studied, they are already
located at the periphery (Wartenberg, 1962; Wischnitzer, 1964b). Perhaps
the stages where perinuclear concentrations of mitochondria occur have
as yet been overlooked. The uniform distribution of mitochondria and their
concentration near the periphery have been verified by means of electron
microscopy.
The distribution of the Golgi complex during the course of oogenesis in
amphibians, summarized recently by Raven (1961), was studied by Hibbard
(1928), Nath (1931), and Saguchi (1932). They reported that in the earliest
stages of oogenesis the Golgi complex is found on one side of the cell nucleus.
The number of Golgi complexes is small at this time, but with the onset
of growth the number is increased. Dispersion of this organelle also commences until they are evenly distributed throughout the cytoplasm. Frequently they accumulate in the periphery of the oocyte. In the mature
egg, Golgi elements were found to be diminished in number and later even
absent. These light microscope findings are not in agreement with those
based on electron-microscope investigations which were cited earlier in
this paper. The discrepancy is possibly due to the identification of other
structures as Golgi material in the light-microscope investigations. Obviously, this problem needs to be reexamined.
It is not yet clear how multiplication of the Golgi complex takes place.
As a rule, it is assumed that it arises by fragmentation, constriction, or
division from existing organelles. Afzelius (1956), utilizing the electron