358
T. A. DETTLAFF
chorda-mesodermal material. Thus the underlying mesoderm of the
auditory region which interacts with the ectoderm before the hindbrain
rudiment, in the anurans plays a relatively greater role in the development of the labyrinth than that in the urodeles and sturgeon fishes. The
same differences in the system of formative interactions are found in
other organogeneses as well ; in the development of the eye and lens in
particular (cf. Twitty, 1955; Lopashov and Stroeva, 1961).
The above-mentioned paper (Dettlaff, 1956) further showed that the
slower tempo of latent differentiation in the ectoderm and chorda-mesoderm in urodele embryos compared to anuran ones corresponded to a
shift of gastrulation onset in the urodeles to earlier cleavage stages than
in the anurans. It was supposed that the combination of cell generations
and developmental stages which could be displaced with respect to each
other is of importance for the determination of formative properties and
interactions. The material presented in the paper makes it possible to
suggest that the state of cytoplasmic segregation during the cleavage
period at the moment of the onset of nuclear morphogenetic function
and the number and the relative sum total duration of the interkinetic
states from the onset of specific nuclear functioning up to the given
developmental stage are the determining factors.
The integral character and co-ordination of the differences in the
tempo of latent differentiation of the derivatives of different germinal
layers which are clearly revealed upon comparison in the newts, axolotl
and frogs, supports this assumption because such shifts affect the
material of all three germ layers in the same way.
VII. Summary
In the survey presented an attempt is made to analyse data on the
early processes of embryo differentiation in amphibians and sturgeon
fishes. Special attention is given to the problems of the morphogenetic
function of nuclei and to the significance of cell generations and time
(duration of individual developmental periods), as differentiation factors.
In order to compare development duration in different animals, the
duration of one mitotic cycle of the first cleavage divisions (r 0 ) was
applied, which mirrors hereditarily determined and species specific
developmental rate, as well as its dependence upon environmental
conditions.
When summarizing the data analysed, it can be said that the duration
of an individual developmental period (periods of cleavage, gastrulation
and neurulation within the average optimal temperature range) in any
animal species is characterized by a definite, relatively steady number
ofr 0 .
T. A. DETTLAFF
chorda-mesodermal material. Thus the underlying mesoderm of the
auditory region which interacts with the ectoderm before the hindbrain
rudiment, in the anurans plays a relatively greater role in the development of the labyrinth than that in the urodeles and sturgeon fishes. The
same differences in the system of formative interactions are found in
other organogeneses as well ; in the development of the eye and lens in
particular (cf. Twitty, 1955; Lopashov and Stroeva, 1961).
The above-mentioned paper (Dettlaff, 1956) further showed that the
slower tempo of latent differentiation in the ectoderm and chorda-mesoderm in urodele embryos compared to anuran ones corresponded to a
shift of gastrulation onset in the urodeles to earlier cleavage stages than
in the anurans. It was supposed that the combination of cell generations
and developmental stages which could be displaced with respect to each
other is of importance for the determination of formative properties and
interactions. The material presented in the paper makes it possible to
suggest that the state of cytoplasmic segregation during the cleavage
period at the moment of the onset of nuclear morphogenetic function
and the number and the relative sum total duration of the interkinetic
states from the onset of specific nuclear functioning up to the given
developmental stage are the determining factors.
The integral character and co-ordination of the differences in the
tempo of latent differentiation of the derivatives of different germinal
layers which are clearly revealed upon comparison in the newts, axolotl
and frogs, supports this assumption because such shifts affect the
material of all three germ layers in the same way.
VII. Summary
In the survey presented an attempt is made to analyse data on the
early processes of embryo differentiation in amphibians and sturgeon
fishes. Special attention is given to the problems of the morphogenetic
function of nuclei and to the significance of cell generations and time
(duration of individual developmental periods), as differentiation factors.
In order to compare development duration in different animals, the
duration of one mitotic cycle of the first cleavage divisions (r 0 ) was
applied, which mirrors hereditarily determined and species specific
developmental rate, as well as its dependence upon environmental
conditions.
When summarizing the data analysed, it can be said that the duration
of an individual developmental period (periods of cleavage, gastrulation
and neurulation within the average optimal temperature range) in any
animal species is characterized by a definite, relatively steady number
ofr 0 .