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SAUL WISCHNITZER
Cytosomes. These are vesicles filled with granular material. Such bodies
are thought to originate from a variety of sources: by pinching off from the
ends of the microvilli, by budding off from the swollen ends of mitochondria,
as derivatives of the vesicles of the Golgi complex, or from the nucleus as
chromidia (see below).
Complex Cytosomes. Each body is a composite consisting of cytosomes,
small vesicles, lamellar membranes, and granules—all enclosed with a
membrane. These structures are considered to be derived from multiple
sources. It is from the complex cytosomes that yolk platelets are thought
to arise. This might occur by a reorganization of the multiple structures
into a crystalline core which makes up the bulk of the yolk platelet.
Chromidia. The cytoplasm of oocytes of the amphibian and other forms
is characterized by the absence of the ergastoplasm. The demonstration
of basophilia by histochemical methods, especially in the perinuclear
region, is thought by Wartenberg (1962) to be due to the presence of free
ribosomes and chromidia. The latter are vesicles, 100 ιημ in diameter,
that have a coarse granular content. They are presumed to be nuclear
products which contain bound RNA and contribute to the formation of the
complex cytosomes.
C. Inclusion Bodies
The developing amphibian oocyte is characterized by an intense intracytoplasmic deposition of yolk, lipids, and glycogen. All these inclusions
are essential for future growth and differentiation because they serve both
as a reservoir of metabolites and as a potential source of energy.
Raven (1961) distinguishes three forms of yolk: carbohydrate, fatty
(lipochondria), and protein yolk (platelets). Carbohydrate yolk is probably
a mucopolysaccharide derivative of glycogen. It is present in the form of
distinct structural entities in insect and fish ova, but in amphibians appears
to be absent.
Most of the inclusion bodies found in the cytoplasm are membranesurrounded structures. This has been conclusively established by electron
microscopy for yolk platelets and pigment granules. In lipochondria and
cortical granules the boundaries are also different in structure from the
contents, but these boundaries have not been established to be distinct
structural entities. Since yolk platelets are the predominant type of inclusion body found in the cytoplasm, they will be discussed first.
1. Yolk Platelets
Yolk platelets are the most prominent of all the cytoplasmic components
of amphibian eggs and embryonic cells. Studies during the last 5 years have
SAUL WISCHNITZER
Cytosomes. These are vesicles filled with granular material. Such bodies
are thought to originate from a variety of sources: by pinching off from the
ends of the microvilli, by budding off from the swollen ends of mitochondria,
as derivatives of the vesicles of the Golgi complex, or from the nucleus as
chromidia (see below).
Complex Cytosomes. Each body is a composite consisting of cytosomes,
small vesicles, lamellar membranes, and granules—all enclosed with a
membrane. These structures are considered to be derived from multiple
sources. It is from the complex cytosomes that yolk platelets are thought
to arise. This might occur by a reorganization of the multiple structures
into a crystalline core which makes up the bulk of the yolk platelet.
Chromidia. The cytoplasm of oocytes of the amphibian and other forms
is characterized by the absence of the ergastoplasm. The demonstration
of basophilia by histochemical methods, especially in the perinuclear
region, is thought by Wartenberg (1962) to be due to the presence of free
ribosomes and chromidia. The latter are vesicles, 100 ιημ in diameter,
that have a coarse granular content. They are presumed to be nuclear
products which contain bound RNA and contribute to the formation of the
complex cytosomes.
C. Inclusion Bodies
The developing amphibian oocyte is characterized by an intense intracytoplasmic deposition of yolk, lipids, and glycogen. All these inclusions
are essential for future growth and differentiation because they serve both
as a reservoir of metabolites and as a potential source of energy.
Raven (1961) distinguishes three forms of yolk: carbohydrate, fatty
(lipochondria), and protein yolk (platelets). Carbohydrate yolk is probably
a mucopolysaccharide derivative of glycogen. It is present in the form of
distinct structural entities in insect and fish ova, but in amphibians appears
to be absent.
Most of the inclusion bodies found in the cytoplasm are membranesurrounded structures. This has been conclusively established by electron
microscopy for yolk platelets and pigment granules. In lipochondria and
cortical granules the boundaries are also different in structure from the
contents, but these boundaries have not been established to be distinct
structural entities. Since yolk platelets are the predominant type of inclusion body found in the cytoplasm, they will be discussed first.
1. Yolk Platelets
Yolk platelets are the most prominent of all the cytoplasmic components
of amphibian eggs and embryonic cells. Studies during the last 5 years have