ULTRASTRUCTURE OF DEVELOPING AMPHIBIAN EGG 159
disclosed the fine structure of the yolk platelets and have shed light on their
morphogenesis.
Each yolk platelet has been shown to consist of three elements: a dense
core, a granular cortex, and an outer membrane (Fig. 19). The core consists
of a crystalline lattice (Fig. 20) that is evident by the periodicity of light
and dark lines having a spacing of about 70 Â (Wischnitzer, 1957; Karasaki
and Komoda, 1958; Karasaki, 1959, 1963a; Ward, 1959, 1962; Wartenberg
and Schmidt, 1961; Wartenberg, 1962). Recently, Karasaki (1963a) has
suggested that the crystalline structure is a simple hexagonal lattice made
up of closely packed cylindrical rods, each of which is 80 Ä in diameter and
160 A in length. A homogeneous granular (or fibrillar) cortex, whose individual elements are about 50 A, surrounds the crystalline core. This layer, in
turn, is surrounded by a limiting membrane 70 A thick. An interspace of
variable width appears to exist between the limiting membrane and the
cortical layer.
2.
Lipochondria
Among the inclusions found in the cytoplasm of amphibian oocytes are
lipid-containing bodies known as lipochondria (Holtfreter, 1946). The
distribution of these bodies during the course of oogenesis in Triturus
viridescens is diagrammatically shown in Fig. 21.
The lipochondria are first seen in immature oocytes as small clusters
that lie in the peripheral or central part of the cytoplasm. The only other
structure visible with the phase-contrast micrcscope at this time are clusters
of mitochondria. In somewhat older oocytes, still devoid of yolk, the individual masses of lipochondria appear to have been separated into individual elements distributed throughout the periphery of the cytoplasm.
In yolk-synthesizing eggs, the lipochondria are once again^ [found in
clusters. These clusters are arranged as a ring around, and some distance
from the nucleus. This ring of lipochondria presumably moves closer toward the nucleus as yolk formation progresses. By the time the cytoplasm
has been filled with yolk, the lipochondrial ring has disappeared and its
individual elements are distributed throughout.
With the electron microscope lipochondria were first seen by Kemp
(1956) in oocytes from Rana pipiens. Subsequently, they have been observed in other anurans as well as in urodeles (see Wischnitzer, 1958; Ward,
1962; Kessel, 1963; Balinsky and Devis, 1963). The lipochondria appear as
irregularly shaped bodies that have a homogeneous consistency and a
dense margin (see Fig. 12). The latter does not present the^structural
characteristics of a true membrane.
disclosed the fine structure of the yolk platelets and have shed light on their
morphogenesis.
Each yolk platelet has been shown to consist of three elements: a dense
core, a granular cortex, and an outer membrane (Fig. 19). The core consists
of a crystalline lattice (Fig. 20) that is evident by the periodicity of light
and dark lines having a spacing of about 70 Â (Wischnitzer, 1957; Karasaki
and Komoda, 1958; Karasaki, 1959, 1963a; Ward, 1959, 1962; Wartenberg
and Schmidt, 1961; Wartenberg, 1962). Recently, Karasaki (1963a) has
suggested that the crystalline structure is a simple hexagonal lattice made
up of closely packed cylindrical rods, each of which is 80 Ä in diameter and
160 A in length. A homogeneous granular (or fibrillar) cortex, whose individual elements are about 50 A, surrounds the crystalline core. This layer, in
turn, is surrounded by a limiting membrane 70 A thick. An interspace of
variable width appears to exist between the limiting membrane and the
cortical layer.
2.
Lipochondria
Among the inclusions found in the cytoplasm of amphibian oocytes are
lipid-containing bodies known as lipochondria (Holtfreter, 1946). The
distribution of these bodies during the course of oogenesis in Triturus
viridescens is diagrammatically shown in Fig. 21.
The lipochondria are first seen in immature oocytes as small clusters
that lie in the peripheral or central part of the cytoplasm. The only other
structure visible with the phase-contrast micrcscope at this time are clusters
of mitochondria. In somewhat older oocytes, still devoid of yolk, the individual masses of lipochondria appear to have been separated into individual elements distributed throughout the periphery of the cytoplasm.
In yolk-synthesizing eggs, the lipochondria are once again^ [found in
clusters. These clusters are arranged as a ring around, and some distance
from the nucleus. This ring of lipochondria presumably moves closer toward the nucleus as yolk formation progresses. By the time the cytoplasm
has been filled with yolk, the lipochondrial ring has disappeared and its
individual elements are distributed throughout.
With the electron microscope lipochondria were first seen by Kemp
(1956) in oocytes from Rana pipiens. Subsequently, they have been observed in other anurans as well as in urodeles (see Wischnitzer, 1958; Ward,
1962; Kessel, 1963; Balinsky and Devis, 1963). The lipochondria appear as
irregularly shaped bodies that have a homogeneous consistency and a
dense margin (see Fig. 12). The latter does not present the^structural
characteristics of a true membrane.