346
T. A. DETTLAFF
A. Latent Differentiation in the Embryos of One Species
developing at Different Temperatures
In the development of cilia (Twitty, 1928) and the lens (Ubisch,
1924a, b; Ten Cate, 1956; Jacobson, 1955, 1958; Woellwarth, 1962) it
has been shown that both the stage at which the ability to develop
independently appears in the rudiment and the degree of determination
of rudiments at the same developmental stage differ in embryos
developing at extremes of temperature. At low temperatures this
ability arises at earlier stages than at higher temperatures. Thus, in
embryos of Ambystoma punctatum developing at 7° C the determination
of the direction of the ciliary beat (Twitty, 1928) takes place between
the 16th and 19th Harrison stages; in embryos developing at room
temperature the determination takes place between the 18th and 21st
stages. At 7° C, the cilia also start functioning at an earlier stage.
In a similar way, the properties of the lens-forming material in
embryos of Rana esculenta grown at 12°, 15°, 18° and 25° C differ (Ten Cate,
1956). At the early neurula stage the rudiment of one eye was removed
from the embryos which were then grown at room temperature (about
18° C). Lenses appeared more frequently and were more differentiated
(of 168 experiments, 125 gave positive results; in 81 of them a lens
vesicle was formed) in the embryos kept at 12°. The 55 experiments at
25° yielded only one lens and 2 lentoids. It seems that the duration of
the exposure to the extreme temperatures may affect the extent of the
difference in the percentage of lenses formed. When the embryos were
kept at 12° and 25° since fertilization, the difference was 50%, while
when kept at these temperatures from the onset of gastrulation the
difference was 36%. Unfortunately, the small numbers of specimens
makes differences found under the action of extreme and average
temperatures unreliable.
In the embryos of Triturus alpestris (Woellwarth, 1962) grown at 14°,
18° and 23° free paired lenses were formed in 68%, 43% and 18% of the
animals, respectively, after the removal of the neural plate and neural
crest rudiments at the early neurula stage.
Ten Cate and Woellwarth thus found a shift in latent differentiation
to an earlier developmental stage when embryos were reared at lower
temperatures and to a later stage at higher temperatures. Somewhat
different data are presented by Jacobson (1955, 1958). He has grown
embryos of the newt Taricha torosa up to the early neurula stage at 25°,
19°, 13°, 9° and 5° C. After removal of the eye rudiment the greatest
number of free lenses appeared in embryos grown at 16° C, fewer
appearing in embryos grown at higher (25° C) and at lower (13°, 9° and
5° C) temperatures. Unfortunately, Jacobson's experimental series are
not completely comparable, since the embryos kept at 5°, 9°, 13° and 25°
T. A. DETTLAFF
A. Latent Differentiation in the Embryos of One Species
developing at Different Temperatures
In the development of cilia (Twitty, 1928) and the lens (Ubisch,
1924a, b; Ten Cate, 1956; Jacobson, 1955, 1958; Woellwarth, 1962) it
has been shown that both the stage at which the ability to develop
independently appears in the rudiment and the degree of determination
of rudiments at the same developmental stage differ in embryos
developing at extremes of temperature. At low temperatures this
ability arises at earlier stages than at higher temperatures. Thus, in
embryos of Ambystoma punctatum developing at 7° C the determination
of the direction of the ciliary beat (Twitty, 1928) takes place between
the 16th and 19th Harrison stages; in embryos developing at room
temperature the determination takes place between the 18th and 21st
stages. At 7° C, the cilia also start functioning at an earlier stage.
In a similar way, the properties of the lens-forming material in
embryos of Rana esculenta grown at 12°, 15°, 18° and 25° C differ (Ten Cate,
1956). At the early neurula stage the rudiment of one eye was removed
from the embryos which were then grown at room temperature (about
18° C). Lenses appeared more frequently and were more differentiated
(of 168 experiments, 125 gave positive results; in 81 of them a lens
vesicle was formed) in the embryos kept at 12°. The 55 experiments at
25° yielded only one lens and 2 lentoids. It seems that the duration of
the exposure to the extreme temperatures may affect the extent of the
difference in the percentage of lenses formed. When the embryos were
kept at 12° and 25° since fertilization, the difference was 50%, while
when kept at these temperatures from the onset of gastrulation the
difference was 36%. Unfortunately, the small numbers of specimens
makes differences found under the action of extreme and average
temperatures unreliable.
In the embryos of Triturus alpestris (Woellwarth, 1962) grown at 14°,
18° and 23° free paired lenses were formed in 68%, 43% and 18% of the
animals, respectively, after the removal of the neural plate and neural
crest rudiments at the early neurula stage.
Ten Cate and Woellwarth thus found a shift in latent differentiation
to an earlier developmental stage when embryos were reared at lower
temperatures and to a later stage at higher temperatures. Somewhat
different data are presented by Jacobson (1955, 1958). He has grown
embryos of the newt Taricha torosa up to the early neurula stage at 25°,
19°, 13°, 9° and 5° C. After removal of the eye rudiment the greatest
number of free lenses appeared in embryos grown at 16° C, fewer
appearing in embryos grown at higher (25° C) and at lower (13°, 9° and
5° C) temperatures. Unfortunately, Jacobson's experimental series are
not completely comparable, since the embryos kept at 5°, 9°, 13° and 25°