168
SAUL WISCHNITZER
take place by blebbing from the outer nuclear membrane of the nuclear
envelope. In the process, this membrane undergoes localized expansion
which creates a bleb (Fig. 23). The bleb increases in size until it remains
attached to the membrane only by a narrow stalk. The process of vesicle
formation is completed when the bleb becomes pinched off as a free-floating
cytoplasmic element. In Triturus, this process involves the formation of
isolated vesicles, whereas in Necturus this process involves the synchronous
liberation of a row of such vesicles (see p. 156). In the latter case, these
become organized into the annulate lamellae. Balinsky and Devis (1963),
based on their studies of oocytes from Xenopus, feel that vesicles are produced by the annulate lamellae. They suggest that this takes place by
swelling at the edges of these membranous sheets which then become
detached as vesicles. They look upon the vesicles as a modified form of
endoplasmic reticulum. An organized network is, however, not existent in
developing oocytes, but develops during the differentiation of embryonic
cells (Sung, 1962).
It is probable that vesicles are derived from several sources. These include the nuclear envelope by blebbing, the annulate lamellae by reorganization, and, according to Wartenberg (1962), the plasmalemma
by pinocytosis and the Golgi complex by separation of the vesicular
components.
Aside from contributing to the formation of the annulate lamellae in
some species, the function of the vesicles remains to be established. The
involvement of specialized vesicles in yolk platelet and pigment formation
is discussed later (p. 171 and p. 174, respectively).
The observation by Wartenberg (1962) of the presence of cytosomes,
complex cytosomes, and chromidia has provided him with the basis of a
dynamic concept of cytoplasmic activity. He feels that the sum total of
these organelles makes up what has been termed the "vacuolar apparatus"
(W. Schmidt, 1961 cited in Wartenberg, 1962). These structures are
considered to be responsible for the uptake, sequestering, and synthesis
of basic materials into the protein yolk platelets and pigment granules.
Thus far, Wartenberg is the only one to have reported the presence of
such organelles in the cytoplasm of amphibian oocytes. His observations,
therefore, await confirmation from other workers using different material.
It is conceivable that the presence of this mechanism for yolk and pigment
formation is limited to urodeles. This is suggested by the following facts.
1. Complex cytosomes were demonstrated by Wartenberg only in oocytes
from Triton.
2. Bodies similar but not identical to complex cytosomes were seen in
Triturus viridescens oocytes (Wischnitzer, unpublished observations,
1958). They may have been overlooked by other workers.
SAUL WISCHNITZER
take place by blebbing from the outer nuclear membrane of the nuclear
envelope. In the process, this membrane undergoes localized expansion
which creates a bleb (Fig. 23). The bleb increases in size until it remains
attached to the membrane only by a narrow stalk. The process of vesicle
formation is completed when the bleb becomes pinched off as a free-floating
cytoplasmic element. In Triturus, this process involves the formation of
isolated vesicles, whereas in Necturus this process involves the synchronous
liberation of a row of such vesicles (see p. 156). In the latter case, these
become organized into the annulate lamellae. Balinsky and Devis (1963),
based on their studies of oocytes from Xenopus, feel that vesicles are produced by the annulate lamellae. They suggest that this takes place by
swelling at the edges of these membranous sheets which then become
detached as vesicles. They look upon the vesicles as a modified form of
endoplasmic reticulum. An organized network is, however, not existent in
developing oocytes, but develops during the differentiation of embryonic
cells (Sung, 1962).
It is probable that vesicles are derived from several sources. These include the nuclear envelope by blebbing, the annulate lamellae by reorganization, and, according to Wartenberg (1962), the plasmalemma
by pinocytosis and the Golgi complex by separation of the vesicular
components.
Aside from contributing to the formation of the annulate lamellae in
some species, the function of the vesicles remains to be established. The
involvement of specialized vesicles in yolk platelet and pigment formation
is discussed later (p. 171 and p. 174, respectively).
The observation by Wartenberg (1962) of the presence of cytosomes,
complex cytosomes, and chromidia has provided him with the basis of a
dynamic concept of cytoplasmic activity. He feels that the sum total of
these organelles makes up what has been termed the "vacuolar apparatus"
(W. Schmidt, 1961 cited in Wartenberg, 1962). These structures are
considered to be responsible for the uptake, sequestering, and synthesis
of basic materials into the protein yolk platelets and pigment granules.
Thus far, Wartenberg is the only one to have reported the presence of
such organelles in the cytoplasm of amphibian oocytes. His observations,
therefore, await confirmation from other workers using different material.
It is conceivable that the presence of this mechanism for yolk and pigment
formation is limited to urodeles. This is suggested by the following facts.
1. Complex cytosomes were demonstrated by Wartenberg only in oocytes
from Triton.
2. Bodies similar but not identical to complex cytosomes were seen in
Triturus viridescens oocytes (Wischnitzer, unpublished observations,
1958). They may have been overlooked by other workers.