CELL DIVISIONS
347
were taken from later stages than those kept at 16° and 19° C. When
transferred to the extreme temperatures directly after fertilization, the
embryos usually died. It seems that these temperatures severely
injure the embryos.
Data are also available which show that, with a change in temperature,
metabolic rate changes parallel to morphological properties (Ten Cate,
1956, and others). Thus it was found by Ten Cate that embryos of Rana
esculenta, during the period from fertilization to the end of neurulation,
consumed at 12° C almost 35% more oxygen than at 25°. On the basis
of his experiments Ten Cate suggested that the rate of latent differentiation (intrinsic development) (at low temperatures—T.D.) could be
correlated with the metabolic rate, and both processes are relatively
independent of morphological differentiation. In his book Ten Cate
states this last conclusion as follows : 'It is suggested that the relatively
smaller inhibition of intrinsic development may be correlated with the
lower temperature coefficient of protein synthesis and of the production
and transfer of energy-rich phosphates which provide the necessary
energy for this synthesis' (p. 245, 1956).
On the other hand, Ten Cate's paper presents data on the duration of
cleavage, gastrulation and neurulation in the embryos of R. esculenta (as
well as of R. temporaria
and Ambystoma
mexicanum)
at different
temperatures which show that with a temperature drop to 12° the
relative durations of the individual developmental periods is disturbed :
the cleavage period is slowed down relatively less than the gastrulation
period (IV, D). In Rana esculenta at 12° and 26° these differences are
considerably greater than in Ambystoma mexicanum at 10° and 26°
though they are present in the axolotl, amounting to several τ χ (IV, A).
It is important that recalculation of the duration of the cleavage period
in terms of r 0 in the axolotl, as in sturgeon species (cf. Dettlaff and
Dettlaff, 1961), shows that the number of τ 0 at low temperatures is not
less and is even more than at average optimal temperatures. Thus, the
diminution in the relative duration of the cleavage period and the
increase in that of gastrulation suggests only that at low temperatures
Q 10 for cleavage is lower than for subsequent development, as was
noticed by Ten Cate. This leads to the conclusion that at 12° cell
division in R. esculenta embryos proceeds faster than the processes of
gastrulation. Correspondingly, R. esculenta embryos at the stage of the
early neurula must contain older cells ; the sum total relative duration
of the interkinetic state of these cells is greater than that at average and,
even more so, at higher temperatures.
Thus apart from a correlation between the level of latent differentiation and 0 2 consumption noticed by Ten Cate, a clear correlation is
revealed between these and a change in the ratio of the processes of
347
were taken from later stages than those kept at 16° and 19° C. When
transferred to the extreme temperatures directly after fertilization, the
embryos usually died. It seems that these temperatures severely
injure the embryos.
Data are also available which show that, with a change in temperature,
metabolic rate changes parallel to morphological properties (Ten Cate,
1956, and others). Thus it was found by Ten Cate that embryos of Rana
esculenta, during the period from fertilization to the end of neurulation,
consumed at 12° C almost 35% more oxygen than at 25°. On the basis
of his experiments Ten Cate suggested that the rate of latent differentiation (intrinsic development) (at low temperatures—T.D.) could be
correlated with the metabolic rate, and both processes are relatively
independent of morphological differentiation. In his book Ten Cate
states this last conclusion as follows : 'It is suggested that the relatively
smaller inhibition of intrinsic development may be correlated with the
lower temperature coefficient of protein synthesis and of the production
and transfer of energy-rich phosphates which provide the necessary
energy for this synthesis' (p. 245, 1956).
On the other hand, Ten Cate's paper presents data on the duration of
cleavage, gastrulation and neurulation in the embryos of R. esculenta (as
well as of R. temporaria
and Ambystoma
mexicanum)
at different
temperatures which show that with a temperature drop to 12° the
relative durations of the individual developmental periods is disturbed :
the cleavage period is slowed down relatively less than the gastrulation
period (IV, D). In Rana esculenta at 12° and 26° these differences are
considerably greater than in Ambystoma mexicanum at 10° and 26°
though they are present in the axolotl, amounting to several τ χ (IV, A).
It is important that recalculation of the duration of the cleavage period
in terms of r 0 in the axolotl, as in sturgeon species (cf. Dettlaff and
Dettlaff, 1961), shows that the number of τ 0 at low temperatures is not
less and is even more than at average optimal temperatures. Thus, the
diminution in the relative duration of the cleavage period and the
increase in that of gastrulation suggests only that at low temperatures
Q 10 for cleavage is lower than for subsequent development, as was
noticed by Ten Cate. This leads to the conclusion that at 12° cell
division in R. esculenta embryos proceeds faster than the processes of
gastrulation. Correspondingly, R. esculenta embryos at the stage of the
early neurula must contain older cells ; the sum total relative duration
of the interkinetic state of these cells is greater than that at average and,
even more so, at higher temperatures.
Thus apart from a correlation between the level of latent differentiation and 0 2 consumption noticed by Ten Cate, a clear correlation is
revealed between these and a change in the ratio of the processes of