ULTRASTRUCTURE OF DEVELOPING AMPHIBIAN EGG 173
Wittek (1952) claimed that during the later part of vitellogenesis lipochondria are formed both near the egg surface and near the nucleus.
Holtfreter (1946) studied the cytoplasmic constituents of mature eggs
from Rana pipiens. He reported that lipid droplets do not exist in the free
form. They were found to be spherical or rodlike bodies, 2-4 μ in diameter,
which exhibited birifringence and were found in clusters. Each of these
bodies was thought to be surrounded by a thin protein coat, which, when
degradated by denaturation enables the lipid to become free.
The intracytoplasmic site of synthesis of the lipochondria has not been
established. It is, however, to be recognized that both the time and place
where these bodies became visible need not coincide with the time and
place where their synthesis has occurred. Rather, lipochondria may possibly
be formed at a time when saturation of the dissolved lipids has been reached
at the site where condensation takes place. Thus, depending on existing
conditions, various organelles can serve to facilitate this process. This may
explain the fact that in ova from different forms lipogenesis has been
associated with various cytoplasmic elements (Raven, 1961).
Ward (1962) has investigated the problem of lipochondria (fatty yolk)
formation by means of electron microscopy; however, his results were not
conclusive. They appear to suggest that lipid material may be formed
within special mitochondria. This, perhaps, takes place in conjunction with
mitochondrial membrane breakdown, followed by extrusion of the lipid
material. Apparently this process takes place so rapidly that it is difficult to
investigate.
Cortical granules are present in sea urchin and fish eggs (see references
in Wartenberg and Schmidt, 1961) as well as in amphibians. In the latter,
they were studied with the light microscope by Motomura (1952), Voss
and Wartenberg (1955), Wartenberg (1956), Rosenbaum (1958), Osanai
(1958, 1960), and Katagiri (1959). These inclusion bodies have been found
in anurans, but have not been observed in urodeles.
Histochemical studies have shown that whether the cortical granules
contain neutral or acid mucopolysaccharides is dependent upon the genus
(Rosenbaum, 1958). The functional significance of the cortical granules
was postulated by Wartenberg and Schmidt (1961). They suggested that
the cortical granules release their contents into the perivitelline space to
form a viscous layer at the time of elevation of the fertilization membrane.
This layer becomes liquefied later by imbibition of water. By this means,
the egg is able to undergo reorientation inside of the fertilization membrane.
In urodeles, where cortical granules are not present, rotation of the
egg within the jelly envelopes also involves rotation of the fertilization
membrane. The latter is associated with the surface of the egg for an extended period of time. This phenomenon may be due to the fact that the
Wittek (1952) claimed that during the later part of vitellogenesis lipochondria are formed both near the egg surface and near the nucleus.
Holtfreter (1946) studied the cytoplasmic constituents of mature eggs
from Rana pipiens. He reported that lipid droplets do not exist in the free
form. They were found to be spherical or rodlike bodies, 2-4 μ in diameter,
which exhibited birifringence and were found in clusters. Each of these
bodies was thought to be surrounded by a thin protein coat, which, when
degradated by denaturation enables the lipid to become free.
The intracytoplasmic site of synthesis of the lipochondria has not been
established. It is, however, to be recognized that both the time and place
where these bodies became visible need not coincide with the time and
place where their synthesis has occurred. Rather, lipochondria may possibly
be formed at a time when saturation of the dissolved lipids has been reached
at the site where condensation takes place. Thus, depending on existing
conditions, various organelles can serve to facilitate this process. This may
explain the fact that in ova from different forms lipogenesis has been
associated with various cytoplasmic elements (Raven, 1961).
Ward (1962) has investigated the problem of lipochondria (fatty yolk)
formation by means of electron microscopy; however, his results were not
conclusive. They appear to suggest that lipid material may be formed
within special mitochondria. This, perhaps, takes place in conjunction with
mitochondrial membrane breakdown, followed by extrusion of the lipid
material. Apparently this process takes place so rapidly that it is difficult to
investigate.
Cortical granules are present in sea urchin and fish eggs (see references
in Wartenberg and Schmidt, 1961) as well as in amphibians. In the latter,
they were studied with the light microscope by Motomura (1952), Voss
and Wartenberg (1955), Wartenberg (1956), Rosenbaum (1958), Osanai
(1958, 1960), and Katagiri (1959). These inclusion bodies have been found
in anurans, but have not been observed in urodeles.
Histochemical studies have shown that whether the cortical granules
contain neutral or acid mucopolysaccharides is dependent upon the genus
(Rosenbaum, 1958). The functional significance of the cortical granules
was postulated by Wartenberg and Schmidt (1961). They suggested that
the cortical granules release their contents into the perivitelline space to
form a viscous layer at the time of elevation of the fertilization membrane.
This layer becomes liquefied later by imbibition of water. By this means,
the egg is able to undergo reorientation inside of the fertilization membrane.
In urodeles, where cortical granules are not present, rotation of the
egg within the jelly envelopes also involves rotation of the fertilization
membrane. The latter is associated with the surface of the egg for an extended period of time. This phenomenon may be due to the fact that the