242
RUTH BELLAIRS
in the follicle cells. Riddle (1911) has calculated that to maintain this
rate during the last phase of development each follicle cell would have
to secrete every half hour a quantity of yolk equal to its own volume.
Secondly, the blood serum and liver of laying hens have been shown
to contain large amounts of lipids and proteins that have properties
closely resembling those of similar materials found in yolk (Entenman
et al., 1938; Sheperd and Hottle, 1949; Shimizu et al., 1957; Abraham
et al., 1960; Mok et al., 1961; Patterson et al., 1962a; Williams, 1962b;
Tsuneo et al., 1962). These substances cannot be found in large quantities in the liver and serum of male birds or non-laying females.
Immunological comparisons have demonstrated that these substances
in blood and yolk are frequently identical (Jukes and Kay, 1932 ; Roepke
and Bushneil, 1936; Schechtman, 1947; Knight and Schechtman, 1954;
Tsuneo et al, 1962; Williams, 1962a; Patterson et al., 1962a, b).
Finally, radioactively labelled materials (serum proteins or phosphorus compounds) which have been injected into the blood of the
mother have also been found subsequently in the yolk (Chargaff, 1942b ;
Abe et al., 1959; Patterson etal., 1962a; SchjeideeiaZ., 1963a-c).
The rate at which the serum proteins are manufactured and passed
into the oocyte is dependent on a number of factors such as the age of
the hen (Roepke and Bushneil, 1936 ; Brandt etal., 1951), its food intake
(Sato et al.. 1962) and its hormone balance (Laskowski, 1938; Clavert,
1958). The permeability of the follicular epithelium also appears to vary
during the growth of the oocyte it contains (see p. 231). It may be of
significance that during the final rapid stage of yolk deposition, the
depth of the follicular epithelium becomes reduced (Table I) and the
intercellular space between follicle cells increases.
The substances that are passed through the follicle cells are the
definitive proteins and lipids from which yolk is formed. Thus, there is
no biochemical synthesis in the oocyte, but merely a morphological
rearrangement of materials into yolk spheres and continuous phase
fluid. The rings of yellow and white yolk are themselves a product of
influences outside the oocyte (see Section II, C). This modern concept of
yolk formation does not agree with theories on the importance of the
Balbiani body, which was thought by some of the earlier workers to be
the site of yolk synthesis.
C. The Vitelline Membrane and Ovulation
The inner layer of the vitelline membrane is formed during the final
growth phase of the oocyte (Bellairs et al., 1963). It is possible that it is
secreted by the follicle cells. It appears to develop between the cell membranes of the follicle and oocyte.
RUTH BELLAIRS
in the follicle cells. Riddle (1911) has calculated that to maintain this
rate during the last phase of development each follicle cell would have
to secrete every half hour a quantity of yolk equal to its own volume.
Secondly, the blood serum and liver of laying hens have been shown
to contain large amounts of lipids and proteins that have properties
closely resembling those of similar materials found in yolk (Entenman
et al., 1938; Sheperd and Hottle, 1949; Shimizu et al., 1957; Abraham
et al., 1960; Mok et al., 1961; Patterson et al., 1962a; Williams, 1962b;
Tsuneo et al., 1962). These substances cannot be found in large quantities in the liver and serum of male birds or non-laying females.
Immunological comparisons have demonstrated that these substances
in blood and yolk are frequently identical (Jukes and Kay, 1932 ; Roepke
and Bushneil, 1936; Schechtman, 1947; Knight and Schechtman, 1954;
Tsuneo et al, 1962; Williams, 1962a; Patterson et al., 1962a, b).
Finally, radioactively labelled materials (serum proteins or phosphorus compounds) which have been injected into the blood of the
mother have also been found subsequently in the yolk (Chargaff, 1942b ;
Abe et al., 1959; Patterson etal., 1962a; SchjeideeiaZ., 1963a-c).
The rate at which the serum proteins are manufactured and passed
into the oocyte is dependent on a number of factors such as the age of
the hen (Roepke and Bushneil, 1936 ; Brandt etal., 1951), its food intake
(Sato et al.. 1962) and its hormone balance (Laskowski, 1938; Clavert,
1958). The permeability of the follicular epithelium also appears to vary
during the growth of the oocyte it contains (see p. 231). It may be of
significance that during the final rapid stage of yolk deposition, the
depth of the follicular epithelium becomes reduced (Table I) and the
intercellular space between follicle cells increases.
The substances that are passed through the follicle cells are the
definitive proteins and lipids from which yolk is formed. Thus, there is
no biochemical synthesis in the oocyte, but merely a morphological
rearrangement of materials into yolk spheres and continuous phase
fluid. The rings of yellow and white yolk are themselves a product of
influences outside the oocyte (see Section II, C). This modern concept of
yolk formation does not agree with theories on the importance of the
Balbiani body, which was thought by some of the earlier workers to be
the site of yolk synthesis.
C. The Vitelline Membrane and Ovulation
The inner layer of the vitelline membrane is formed during the final
growth phase of the oocyte (Bellairs et al., 1963). It is possible that it is
secreted by the follicle cells. It appears to develop between the cell membranes of the follicle and oocyte.