236
RUTH BELLAIRS
blue. By electron microscopy they can each be seen to be bounded by a
membrane (Bellairs and Greenfield, unpublished). Gradually patches of
material appear within them which stain densely with fat stains
(Konopacka, 1933), and the vacuoles then become recognizable as yolk
spheres.
4. The Role of Mitochondria and Golgi Apparatus in Yolk Sphere Formation
Several authors have considered that some at least of the yolk spheres
are formed directly by transformation of mitochondria (van Durme,
1914; Brambell, 1926; Varma, 1954). Such a possibility is reminiscent
of the situation in Amphibia where it appears from electron microscopy
that yolk may develop within mitochondria (e.g. Ward, 1962). Sluiter
(1940) who examined both living and fixed oocytes from hens, was unable to find any evidence that the mitochondria give rise directly to yolk.
Others have suggested, however, that the mitochondria merely
'intervene' in yolk formation (Agarwal, 1953). Schjeide et al. (1963 a-c)
have suggested from an electron microscopical study that structures
which they believe to be pre-mitochondria (see below) penetrate into
the yolk vacuoles and take part in yolk formation. From my own
studies (see below) I am, however, doubtful as to whether these structures are really 'pre-mitochondria'.
In an electron microscopical study of the oocyte, Bellairs and Greenfield (unpublished) have found no evidence to support the idea that yolk
can form by conversion of mitochondria. Nevertheless, it seems reasonable to suppose that both the mitochondria and the Golgi apparatus
may play a role in yolk formation since they lie around the periphery
of the oocyte, in a strategic position to intercept and influence new
materials entering the oocyte.
After the dispersal of the Balbiani body there is an increase in the
numbers of both mitochondria and of Golgi apparati. The mechanism
of formation of both these organelles still remains to be elucidated by
electron microscopy. It has, however, been suggested that Golgi
apparati actively migrate from the follicle cells into the oocyte (Brambell, 1926; Guraya, 1957). A similar suggestion has been made for
mitochondria (Varma, 1954). With the benefit of electron microscopical
techniques, it has not been possible to substantiate these hypotheses
(Bellairs and Greenfield, unpublished). It has also been suggested in the
literature that intercellular bridges exist between the follicle cell and
oocyte (Kemp, 1958). This observation has not been confirmed (Press,
1959; Schjeide and McCandless 1962; Schjeide et al., 1963a-c; Bellairs
and Greenfield, unpublished). There is, however, evidence to suggest that
certain bodies do pass from follicle to oocyte even in the pre-yolk period
of oogenesis. These structures are lining bodies and granules as follows.
RUTH BELLAIRS
blue. By electron microscopy they can each be seen to be bounded by a
membrane (Bellairs and Greenfield, unpublished). Gradually patches of
material appear within them which stain densely with fat stains
(Konopacka, 1933), and the vacuoles then become recognizable as yolk
spheres.
4. The Role of Mitochondria and Golgi Apparatus in Yolk Sphere Formation
Several authors have considered that some at least of the yolk spheres
are formed directly by transformation of mitochondria (van Durme,
1914; Brambell, 1926; Varma, 1954). Such a possibility is reminiscent
of the situation in Amphibia where it appears from electron microscopy
that yolk may develop within mitochondria (e.g. Ward, 1962). Sluiter
(1940) who examined both living and fixed oocytes from hens, was unable to find any evidence that the mitochondria give rise directly to yolk.
Others have suggested, however, that the mitochondria merely
'intervene' in yolk formation (Agarwal, 1953). Schjeide et al. (1963 a-c)
have suggested from an electron microscopical study that structures
which they believe to be pre-mitochondria (see below) penetrate into
the yolk vacuoles and take part in yolk formation. From my own
studies (see below) I am, however, doubtful as to whether these structures are really 'pre-mitochondria'.
In an electron microscopical study of the oocyte, Bellairs and Greenfield (unpublished) have found no evidence to support the idea that yolk
can form by conversion of mitochondria. Nevertheless, it seems reasonable to suppose that both the mitochondria and the Golgi apparatus
may play a role in yolk formation since they lie around the periphery
of the oocyte, in a strategic position to intercept and influence new
materials entering the oocyte.
After the dispersal of the Balbiani body there is an increase in the
numbers of both mitochondria and of Golgi apparati. The mechanism
of formation of both these organelles still remains to be elucidated by
electron microscopy. It has, however, been suggested that Golgi
apparati actively migrate from the follicle cells into the oocyte (Brambell, 1926; Guraya, 1957). A similar suggestion has been made for
mitochondria (Varma, 1954). With the benefit of electron microscopical
techniques, it has not been possible to substantiate these hypotheses
(Bellairs and Greenfield, unpublished). It has also been suggested in the
literature that intercellular bridges exist between the follicle cell and
oocyte (Kemp, 1958). This observation has not been confirmed (Press,
1959; Schjeide and McCandless 1962; Schjeide et al., 1963a-c; Bellairs
and Greenfield, unpublished). There is, however, evidence to suggest that
certain bodies do pass from follicle to oocyte even in the pre-yolk period
of oogenesis. These structures are lining bodies and granules as follows.