CELL DIVISIONS
341
TABLE I
Dimensionless characteristics of the duration of the periods of cleavage (TI/T 0 ),
gastrulation (τπ - TI/T 0 ) and neurulation (rm -τπ/τ 0 ) in amphibians and sturgeon
fishes
Species
t° C. τ 0 min.
ΤΙ TU - ΤΙ
το
r 0
ΤΙΠ - TU
A
,,
Author
το
Comments
Rana terrestris 131
88
23-24 27
13-14
Skoblina
τ η from
insemination
Ran a pipiens
18-6
±01
57
23
24
16
from J. Moore
τ η from
the onset
of the first
division
>»
19-9
52
23
21
16
>»
»»
±0-2
Rana palustris
18-6
±01
61
23-6 19
21
>>
»>
»»
19-9
±0-2
53
22-6 20-21 21
»>
ft
Ambystoma
18
105
18-8 17
8
Skoblina
τ η from
mexicanum
insemination
Trituras
18
90
<19·3* 12
15-3
from Gallien
»»
helveticus
and Bidaud
Acipenser
20
37-5
20-0 18-19
7-8
Dettlaff
»»
stellatus
Acipenser
18
50-3
20-3 18-20
8-9
»»
»»
güldenstädti
Huso huso
12-7
77
22· 1 21-6
Chulitskaya
>»
mexicanum is shorter than in the three anuran species ; of the twourodeles,
Triturus has a smaller value than
Ambystoma.^
The duration of neurulation is more difficult to compare as its end is
less clearly determined, and different authors regard different developmental stages as the end of neurulation.
When the duration of neurulation is expressed with standard criteria
(Skoblina) it is shorter in Ambystoma mexicanum in terms of r 0 than in
Rana
terrestris.
In future, such data need to be augmented and obtained at several
* In this case the appearance of the blastopore lip is revealed not by accumulation of
pigment, as in the case of axolotl and Rana terrestris in the experiments of Miss Skoblina,
but the stage of a very small depresion of it was taken as the onset of gastrulation.
Judging by the data obtained by Knight (1938), in Triturus alpestris (= helveticus)
about 4 hours elapse between the first appearance of the outline of the dorsal blastopore
lip and the stage accepted by Gallien and Bidaud (Fig. 12). Thus, taking the same criteria
for the onset of gastrulation, TI/TI for Triturus helveticus is somewhat less than 19-3
while ——— value is, correspondingly, over 12.
T
o
ΐ When the characteristics of the duration of different developmental periods is expressed not in τ 0 but in the fractions of the whole developmental period from insemination up to the end of neurulation (τ η /τιπ) as Ten Cate has done (1956), these differences
are hidden, since the relative value of τπι is different in different species.
341
TABLE I
Dimensionless characteristics of the duration of the periods of cleavage (TI/T 0 ),
gastrulation (τπ - TI/T 0 ) and neurulation (rm -τπ/τ 0 ) in amphibians and sturgeon
fishes
Species
t° C. τ 0 min.
ΤΙ TU - ΤΙ
το
r 0
ΤΙΠ - TU
A
,,
Author
το
Comments
Rana terrestris 131
88
23-24 27
13-14
Skoblina
τ η from
insemination
Ran a pipiens
18-6
±01
57
23
24
16
from J. Moore
τ η from
the onset
of the first
division
>»
19-9
52
23
21
16
>»
»»
±0-2
Rana palustris
18-6
±01
61
23-6 19
21
>>
»>
»»
19-9
±0-2
53
22-6 20-21 21
»>
ft
Ambystoma
18
105
18-8 17
8
Skoblina
τ η from
mexicanum
insemination
Trituras
18
90
<19·3* 12
15-3
from Gallien
»»
helveticus
and Bidaud
Acipenser
20
37-5
20-0 18-19
7-8
Dettlaff
»»
stellatus
Acipenser
18
50-3
20-3 18-20
8-9
»»
»»
güldenstädti
Huso huso
12-7
77
22· 1 21-6
Chulitskaya
>»
mexicanum is shorter than in the three anuran species ; of the twourodeles,
Triturus has a smaller value than
Ambystoma.^
The duration of neurulation is more difficult to compare as its end is
less clearly determined, and different authors regard different developmental stages as the end of neurulation.
When the duration of neurulation is expressed with standard criteria
(Skoblina) it is shorter in Ambystoma mexicanum in terms of r 0 than in
Rana
terrestris.
In future, such data need to be augmented and obtained at several
* In this case the appearance of the blastopore lip is revealed not by accumulation of
pigment, as in the case of axolotl and Rana terrestris in the experiments of Miss Skoblina,
but the stage of a very small depresion of it was taken as the onset of gastrulation.
Judging by the data obtained by Knight (1938), in Triturus alpestris (= helveticus)
about 4 hours elapse between the first appearance of the outline of the dorsal blastopore
lip and the stage accepted by Gallien and Bidaud (Fig. 12). Thus, taking the same criteria
for the onset of gastrulation, TI/TI for Triturus helveticus is somewhat less than 19-3
while ——— value is, correspondingly, over 12.
T
o
ΐ When the characteristics of the duration of different developmental periods is expressed not in τ 0 but in the fractions of the whole developmental period from insemination up to the end of neurulation (τ η /τιπ) as Ten Cate has done (1956), these differences
are hidden, since the relative value of τπι is different in different species.