DEVELOPMENT OF GASTROPODS
15
When Limnaea eggs are treated with hypertonic solutions, vesicles
and blebs appear on their surface (Raven and Mighorst, 1946 ; Grasveld,
1949). They may become entirely separated from the egg, and often fuse
with each other to larger vesicles. These vesicles have a clear fluid
content, but are separated from the outer medium by a thin film,
probably of a phosphatide nature.
When decapsulated Limnaea
eggs are put in Ca-free solutions,
cleavage takes an abnormal course. The blastomeres remain spherical
and do not flatten against each other. The vitelline membrane detaches
itself from the egg surface along the cleavage furrows. The cells lose their
coherence at later stages and fall apart into a loose aggregate of spherical
cells, loosely surrounded by the vitelline membrane. Addition of CaCl 2
at a concentration of 0-005 per cent or more gives normal cleavage and
development until the gastrula stage (Raven and Klomp, 1946; Hudig,
1946; Grasveld, 1949). Treatment of the eggs in their capsule fluid with
Na-oxalate or Na-citrate produces similar aberrations of cleavage
(Stalfoort, 1952). If the eggs are pretreated with a strong CaCl 2 solution,
normal cleavage may occur in distilled water (Raven and Mighorst,
1946). It has been shown by means of the centrifugation method that
CaCl 2 in high concentrations (0-01-0-15 M) increases the rigidity of the
egg cortex (de Vries, 1947).
It is evident that calcium is essential for preserving the normal
properties of the egg cortex. This role of calcium may, to a certain
extent, be taken over by magnesium, and also by lithium in certain
concentrations (de Groot, 1948; Grasveld, 1949). Sodium, on the
contrary, always gives abnormal cleavage, potassium still more abnormal
cleavage. The sequence Ca
If Limnaea eggs are treated at early stages for 24 hours with weak
concentrations of lithium chloride, embryos with characteristic malformations of certain organs develop. With higher concentrations,
gastrulation is inhibited and so-called exogastrulae are produced. With
still higher concentrations, development is arrested at early stages and
the eggs die (Raven, 1942).
A comparison of egg mortality after treatment with various alkali
metal ions (Raven et al., 1956) showed that in each case with increasing
concentration of the cation an S-shaped mortality curve was obtained.
But the lethal concentrations were very different, and increased in the
order Li
by Bungenberg de Jong (1949) with respect to certain di-complex
colloid systems. The water content and stability of these systems are
15
When Limnaea eggs are treated with hypertonic solutions, vesicles
and blebs appear on their surface (Raven and Mighorst, 1946 ; Grasveld,
1949). They may become entirely separated from the egg, and often fuse
with each other to larger vesicles. These vesicles have a clear fluid
content, but are separated from the outer medium by a thin film,
probably of a phosphatide nature.
When decapsulated Limnaea
eggs are put in Ca-free solutions,
cleavage takes an abnormal course. The blastomeres remain spherical
and do not flatten against each other. The vitelline membrane detaches
itself from the egg surface along the cleavage furrows. The cells lose their
coherence at later stages and fall apart into a loose aggregate of spherical
cells, loosely surrounded by the vitelline membrane. Addition of CaCl 2
at a concentration of 0-005 per cent or more gives normal cleavage and
development until the gastrula stage (Raven and Klomp, 1946; Hudig,
1946; Grasveld, 1949). Treatment of the eggs in their capsule fluid with
Na-oxalate or Na-citrate produces similar aberrations of cleavage
(Stalfoort, 1952). If the eggs are pretreated with a strong CaCl 2 solution,
normal cleavage may occur in distilled water (Raven and Mighorst,
1946). It has been shown by means of the centrifugation method that
CaCl 2 in high concentrations (0-01-0-15 M) increases the rigidity of the
egg cortex (de Vries, 1947).
It is evident that calcium is essential for preserving the normal
properties of the egg cortex. This role of calcium may, to a certain
extent, be taken over by magnesium, and also by lithium in certain
concentrations (de Groot, 1948; Grasveld, 1949). Sodium, on the
contrary, always gives abnormal cleavage, potassium still more abnormal
cleavage. The sequence Ca
If Limnaea eggs are treated at early stages for 24 hours with weak
concentrations of lithium chloride, embryos with characteristic malformations of certain organs develop. With higher concentrations,
gastrulation is inhibited and so-called exogastrulae are produced. With
still higher concentrations, development is arrested at early stages and
the eggs die (Raven, 1942).
A comparison of egg mortality after treatment with various alkali
metal ions (Raven et al., 1956) showed that in each case with increasing
concentration of the cation an S-shaped mortality curve was obtained.
But the lethal concentrations were very different, and increased in the
order Li
by Bungenberg de Jong (1949) with respect to certain di-complex
colloid systems. The water content and stability of these systems are