CELL DIVISIONS
351
duration of the interkinetic activity of the cells affect the qualitative
peculiarity of the developing structures.
The important role of ooplasmic segregation in the determination of
the qualitative peculiarity of structures is clearly revealed in the case of
the differentiation of the chorda mesodermal complex of amphibia.
Unlike the entoderm, the early latent differentiation of the chorda
mesodermal complex is not correlated with a considerable prolongation
of the interkinetic state of their cells during asynchronous division but is
determined by synthetic processes realized during the period of oogenesis
and terminated by a strict localization of corresponding cytoplasmic
components during the period of fertilization (Ancel and Vintemberger,
1948 ; cf. also Devillers, 1960, and Clavert, 1961).
E. Latent Differentiation of Rudiments in Embryos of
Different Systematic Groups
The correlation between the differences in the ratio of cell divisions to
developmental stage, on the one hand, and the differences in the rate of
latent differentiation on the other, is most clearly revealed when they
are compared in the embryos of the newt, axolotl and frog (Dettlaff,
1956). At the same time it was shown in the embryos of sturgeon and
sevruga that a similarity in the ratio of cell generation to developmental
stages in closely related animal species corresponds to a similarity in the
rate of latent differentiation (Chulitskaya, 1961a, b).
Latent Differentiation of the Ear Ectoderm
Let us now analyse as an example the latent differentiation of the
rudiment of the labyrinth studied in detail in the Amphibia (for
literature see Yntema, 1955) and in sturgeon fishes (Ginsburg and
Dettlaff, 1944; Chulitskaya, 1961a, b, 1962).
It was shown in the embryos of ten amphibian species (Ginsburg,
1946b, c, 1950a, b) that upon transplantation of ear ectoderm from
subsequent developmental stages in the place of belly ectoderm, the
frequency of the formation, size and differentiation of the ear vesicles in
different species at the same stages are different. During its development,
the ear ectoderm undergoes induction successively from two sources : at
the end of gastrulation and during the whole of neurulation, from the
mesoderm underlying the ectoderm of the auditory region ; and in the
late neurula stage from the hindbrain rudiment (Ginsburg, 1946a, b;
Yntema, 1946, 1950). In urodeles latent differentiation of the material
of the labyrinth passes correspondingly through two clearly distinct
stages : upon transplantation of the material prior to its contact with the
brain rudiment it forms, in a small percentage of cases, small ear
vesicles devoid of sensory areas ; upon transplantation after contact with
351
duration of the interkinetic activity of the cells affect the qualitative
peculiarity of the developing structures.
The important role of ooplasmic segregation in the determination of
the qualitative peculiarity of structures is clearly revealed in the case of
the differentiation of the chorda mesodermal complex of amphibia.
Unlike the entoderm, the early latent differentiation of the chorda
mesodermal complex is not correlated with a considerable prolongation
of the interkinetic state of their cells during asynchronous division but is
determined by synthetic processes realized during the period of oogenesis
and terminated by a strict localization of corresponding cytoplasmic
components during the period of fertilization (Ancel and Vintemberger,
1948 ; cf. also Devillers, 1960, and Clavert, 1961).
E. Latent Differentiation of Rudiments in Embryos of
Different Systematic Groups
The correlation between the differences in the ratio of cell divisions to
developmental stage, on the one hand, and the differences in the rate of
latent differentiation on the other, is most clearly revealed when they
are compared in the embryos of the newt, axolotl and frog (Dettlaff,
1956). At the same time it was shown in the embryos of sturgeon and
sevruga that a similarity in the ratio of cell generation to developmental
stages in closely related animal species corresponds to a similarity in the
rate of latent differentiation (Chulitskaya, 1961a, b).
Latent Differentiation of the Ear Ectoderm
Let us now analyse as an example the latent differentiation of the
rudiment of the labyrinth studied in detail in the Amphibia (for
literature see Yntema, 1955) and in sturgeon fishes (Ginsburg and
Dettlaff, 1944; Chulitskaya, 1961a, b, 1962).
It was shown in the embryos of ten amphibian species (Ginsburg,
1946b, c, 1950a, b) that upon transplantation of ear ectoderm from
subsequent developmental stages in the place of belly ectoderm, the
frequency of the formation, size and differentiation of the ear vesicles in
different species at the same stages are different. During its development,
the ear ectoderm undergoes induction successively from two sources : at
the end of gastrulation and during the whole of neurulation, from the
mesoderm underlying the ectoderm of the auditory region ; and in the
late neurula stage from the hindbrain rudiment (Ginsburg, 1946a, b;
Yntema, 1946, 1950). In urodeles latent differentiation of the material
of the labyrinth passes correspondingly through two clearly distinct
stages : upon transplantation of the material prior to its contact with the
brain rudiment it forms, in a small percentage of cases, small ear
vesicles devoid of sensory areas ; upon transplantation after contact with