344
T. A. DETTLAFF
favour of the white sturgeon. The differences described between the
white sturgeon, on the one hand, and sevruga and sturgeon, on the
other (Dettlaff and Dettlaff, 1960, 1961; Chulitskaya, 1961) are smaller
than those between Ambystoma mexicanum and Rana terrestris (data of
Skoblina, 1964) and smaller than those between Rana terrestris and
Triturus helveticus (data of Gallien and Bidaud, 1959) and
Triturus
vulgaris (data of Dettlaff, 1956) (Tables I and II).
When comparing the values of TJ/TQ, Τ Π - TJ/TO and τ ΙΠ - τ π /τ 0 in R.
terrestris, Ambystoma mexicanum, Triturus helveticus, sturgeon, sevruga
and white sturgeon, at average spawning temperatures for each species,
it can be seen that the values for sturgeon and sevruga are somewhat
greater than those for axolotl and smaller than those for frog; the
values for white sturgeon though greater than those for the sturgeon and
sevruga are nevertheless smaller than for Rana terrestris (Table I). At the
same time, a comparison of the number of nuclei in central sagittal
sections through the sturgeon species and amphibian embryos at the
very beginning of gastrulation (data of Dettlaff, 1956, Kroenig, 1960,
Chulitskaya, 1961) showed that in sections of relatively the same
thickness the same or even a somewhat greater number of nuclei is
found in the sevruga and sturgeon than in Rana terrestris ; the number is
twice that found in the axolotl and four and a half times that of the
newt. These data need making more precise, especially by a stricter
control of temperature to within the average range in the amphibians.
The fact that at a lower TJ/TO value by the onset of gastrulation the sturgeon
or sevruga embryo contains the same or a somewhat greater number of
cells than that of R. terrestris suggests either that the former have a
greater number of synchronous divisions or that their mitotic index
during the asynchronous divisions is higher than that in R. terrestris.
This would imply in both cases that the relative duration of interkinetic
states of cells up to the onset of gastrulation is smaller in the sturgeon
and sevruga than in R. terrestris, being similar to or perhaps less than
that in the axolotl.
It should be added that in the embryos of sturgeon, sevruga and
white sturgeon, as well as in the embryo of the frog, the percentage of
cells dividing during gastrulation and neurulation is smaller than in the
axolotl embryo and considerably smaller than in the newt embryo. In
other words, the interkinetic state of the nuclei in the embryos of
sturgeon species and frogs makes up a relatively larger portion of the
period of gastrulation and neurulation than in the newt. Thus, among
the amphibians and sturgeon species, animals are encountered with a
different ratio between cell division and formative processes. The
processes of gastrulation and neurulation start in newts after fewer cell
divisions, and at the same stages of gastrulation and neurulation their
T. A. DETTLAFF
favour of the white sturgeon. The differences described between the
white sturgeon, on the one hand, and sevruga and sturgeon, on the
other (Dettlaff and Dettlaff, 1960, 1961; Chulitskaya, 1961) are smaller
than those between Ambystoma mexicanum and Rana terrestris (data of
Skoblina, 1964) and smaller than those between Rana terrestris and
Triturus helveticus (data of Gallien and Bidaud, 1959) and
Triturus
vulgaris (data of Dettlaff, 1956) (Tables I and II).
When comparing the values of TJ/TQ, Τ Π - TJ/TO and τ ΙΠ - τ π /τ 0 in R.
terrestris, Ambystoma mexicanum, Triturus helveticus, sturgeon, sevruga
and white sturgeon, at average spawning temperatures for each species,
it can be seen that the values for sturgeon and sevruga are somewhat
greater than those for axolotl and smaller than those for frog; the
values for white sturgeon though greater than those for the sturgeon and
sevruga are nevertheless smaller than for Rana terrestris (Table I). At the
same time, a comparison of the number of nuclei in central sagittal
sections through the sturgeon species and amphibian embryos at the
very beginning of gastrulation (data of Dettlaff, 1956, Kroenig, 1960,
Chulitskaya, 1961) showed that in sections of relatively the same
thickness the same or even a somewhat greater number of nuclei is
found in the sevruga and sturgeon than in Rana terrestris ; the number is
twice that found in the axolotl and four and a half times that of the
newt. These data need making more precise, especially by a stricter
control of temperature to within the average range in the amphibians.
The fact that at a lower TJ/TO value by the onset of gastrulation the sturgeon
or sevruga embryo contains the same or a somewhat greater number of
cells than that of R. terrestris suggests either that the former have a
greater number of synchronous divisions or that their mitotic index
during the asynchronous divisions is higher than that in R. terrestris.
This would imply in both cases that the relative duration of interkinetic
states of cells up to the onset of gastrulation is smaller in the sturgeon
and sevruga than in R. terrestris, being similar to or perhaps less than
that in the axolotl.
It should be added that in the embryos of sturgeon, sevruga and
white sturgeon, as well as in the embryo of the frog, the percentage of
cells dividing during gastrulation and neurulation is smaller than in the
axolotl embryo and considerably smaller than in the newt embryo. In
other words, the interkinetic state of the nuclei in the embryos of
sturgeon species and frogs makes up a relatively larger portion of the
period of gastrulation and neurulation than in the newt. Thus, among
the amphibians and sturgeon species, animals are encountered with a
different ratio between cell division and formative processes. The
processes of gastrulation and neurulation start in newts after fewer cell
divisions, and at the same stages of gastrulation and neurulation their