340
T. A. DETTLAFF
chronous division without changing the rate of division of sea urchin
eggs. In the eggs of Paracentrotus lividus two synchronous divisions were
added by the action of Li ions in the experiments of Agrell (1956).
It is worth mentioning that when acting upon the cells of onion roots,
Li ions decrease the duration of the stage of resting nucleus.
A
relatively smaller number of prophases and a greater number of metaand especially telophases were found in 0· 1 % LiCl solution (Korovina
and Dempel, 1945).
In sevruga eggs, according to preliminary data of the present author
Li ions delay development: gastrulation, neurulation and subsequent
developmental stages in the embryos start later. The delay is greater the
higher the LiCl concentration. Within certain limits of concentration
this delay, however, is not accompanied by any disturbances. Whether
Li ions bring about an increase in the number of synchronous cleavage
divisions in sevruga embryos, as they do in sea urchins, is not clear at
the present time.
E. Ratio of the Durations of Cell Division, Gastrulation and Neurulation in
Various Representatives of Amphibians and Sturgeon Fishes
The relative duration of different developmental periods, including
those of cleavage, gastrulation and neurulation, while having a rather
constant value for each animal species under optimal conditions, can
differ significantly between different animal species. Their dimensionless
character when expressed in terms of r 0 makes it possible (cf. Dettlaff
and Dettlaff, 1961) to compare their duration in different animals.
Unfortunately, there are only a few data available in the literature
which can be used for this comparison.
Table I presents the dimensionless characteristics of the cleavage
(
T
i/
T
o)> gastrulation (r n - T^/TQ and neurulation (τ ΙΠ - τ π )/τ 0 periods for
Ambystoma mexicanum and Rana terrestris, according to the data of
Skoblina (1964), who has specially studied this problem. For comparison
values of these ratios for Rana pipiens and Rana palustris are also
included in the table ; they were recalculated by the present author from
the data on the duration τ τ , Τ π and τ ΙΠ presented by J. Moore (1939),
the value of r 0 at the same temperatures being obtained from J. Moore
(1941). For urodeles, apart from Ambystoma
mexicanum,
data are
recalculated for Triturus helveticus from the material presented by
Gallien and Bidaud (1959); from this, values of τ Ι? τ π , τ ΠΙ for
advanced eggs were taken, while the r T value was kindly sent to me by
Professor Gallien.
It can easily be seen from the table that the duration of the periods of
cleavage and gastrulation in Triturus
helveticus and
Ambystoma
T. A. DETTLAFF
chronous division without changing the rate of division of sea urchin
eggs. In the eggs of Paracentrotus lividus two synchronous divisions were
added by the action of Li ions in the experiments of Agrell (1956).
It is worth mentioning that when acting upon the cells of onion roots,
Li ions decrease the duration of the stage of resting nucleus.
A
relatively smaller number of prophases and a greater number of metaand especially telophases were found in 0· 1 % LiCl solution (Korovina
and Dempel, 1945).
In sevruga eggs, according to preliminary data of the present author
Li ions delay development: gastrulation, neurulation and subsequent
developmental stages in the embryos start later. The delay is greater the
higher the LiCl concentration. Within certain limits of concentration
this delay, however, is not accompanied by any disturbances. Whether
Li ions bring about an increase in the number of synchronous cleavage
divisions in sevruga embryos, as they do in sea urchins, is not clear at
the present time.
E. Ratio of the Durations of Cell Division, Gastrulation and Neurulation in
Various Representatives of Amphibians and Sturgeon Fishes
The relative duration of different developmental periods, including
those of cleavage, gastrulation and neurulation, while having a rather
constant value for each animal species under optimal conditions, can
differ significantly between different animal species. Their dimensionless
character when expressed in terms of r 0 makes it possible (cf. Dettlaff
and Dettlaff, 1961) to compare their duration in different animals.
Unfortunately, there are only a few data available in the literature
which can be used for this comparison.
Table I presents the dimensionless characteristics of the cleavage
(
T
i/
T
o)> gastrulation (r n - T^/TQ and neurulation (τ ΙΠ - τ π )/τ 0 periods for
Ambystoma mexicanum and Rana terrestris, according to the data of
Skoblina (1964), who has specially studied this problem. For comparison
values of these ratios for Rana pipiens and Rana palustris are also
included in the table ; they were recalculated by the present author from
the data on the duration τ τ , Τ π and τ ΙΠ presented by J. Moore (1939),
the value of r 0 at the same temperatures being obtained from J. Moore
(1941). For urodeles, apart from Ambystoma
mexicanum,
data are
recalculated for Triturus helveticus from the material presented by
Gallien and Bidaud (1959); from this, values of τ Ι? τ π , τ ΠΙ for
advanced eggs were taken, while the r T value was kindly sent to me by
Professor Gallien.
It can easily be seen from the table that the duration of the periods of
cleavage and gastrulation in Triturus
helveticus and
Ambystoma