15. E M B R Y O G E N E S I S in vitro
579
leading from the heart or whether they form independently in the
vascular area and in the allantois. From experiments with the culture
of allantoic buds in a hypoblastic vesicle, the complete destruction of
the two developing heart-rudiments showed that, in the vitelline area,
as in the allantois, the vessels are formed independently of the heart.
Vascular buds are also formed in the region of the aortae. The large
vessels leading from the heart are formed first at the heart; they then
join the already formed vascular buds, and establish a co-ordinated
circulation. The formation of the heart, therefore, is not the starting
point of the whole vascular organization of the embryo and its membranes, but only a special part of this organization.
In another experiment, Jolly destroyed one of the cardiac rudiments.
The other rudiment, originally situated laterally, showed a tendency
to move towards the mid-line; it established a connexion with the side
deprived of its rudiment, and could, in certain cases, form a complete
S-shaped heart, and initiate circulation through the whole of the area
vasculosa. However, it has not been shown that such a heart, if it
continued to develop, could in fact form the compartments and the
differentiations of a normal heart.
In a recent paper, New and Stein (1964) have cultured embryos of
rats and mice on clots of plasma and embryo extract. It did not matter
whether the embryo extract utilized in the media originated from
chicken, mouse or rats. Embryos of both species, taken at the primitive
streak stage, developed up to the stage of several somites. Mouse
embryos, explanted from 1 to 7 somites, developed a blood circulation
(72%) and 3 3 % reached the limb-bud stage. Rat embryos, explanted
from 6 to 12 somites stages, differentiated fore-limbs and 25 to 30
somites.
D .
R E I M P L A N T A T I O N
O F E G G S I N T H E U T E R U S
A F T E R
E X P E R I M E N T S
W I T H
T H E M
I N IJV VITRO
C U L T U R E
Since it has proved impossible to continue development of eggs for
a long period in vitro, several authors have reimplanted mammalian
eggs into the uterus after a period in vitro. Eggs have been reimplanted
either directly after they were removed or after a certain time in
culture.
The first type of investigation (implantation directly after removal)
was inaugurated by Nicholas and Hall (1934, 1942). These authors
separated the first two blastomeres from an egg of a rat; each of the
two blastomeres could give rise to a complete embryo. Two juxtaposed
eggs developed into a single embryo, properly proportioned but double
the size of a normal one. Analogous experiments with regard to the
579
leading from the heart or whether they form independently in the
vascular area and in the allantois. From experiments with the culture
of allantoic buds in a hypoblastic vesicle, the complete destruction of
the two developing heart-rudiments showed that, in the vitelline area,
as in the allantois, the vessels are formed independently of the heart.
Vascular buds are also formed in the region of the aortae. The large
vessels leading from the heart are formed first at the heart; they then
join the already formed vascular buds, and establish a co-ordinated
circulation. The formation of the heart, therefore, is not the starting
point of the whole vascular organization of the embryo and its membranes, but only a special part of this organization.
In another experiment, Jolly destroyed one of the cardiac rudiments.
The other rudiment, originally situated laterally, showed a tendency
to move towards the mid-line; it established a connexion with the side
deprived of its rudiment, and could, in certain cases, form a complete
S-shaped heart, and initiate circulation through the whole of the area
vasculosa. However, it has not been shown that such a heart, if it
continued to develop, could in fact form the compartments and the
differentiations of a normal heart.
In a recent paper, New and Stein (1964) have cultured embryos of
rats and mice on clots of plasma and embryo extract. It did not matter
whether the embryo extract utilized in the media originated from
chicken, mouse or rats. Embryos of both species, taken at the primitive
streak stage, developed up to the stage of several somites. Mouse
embryos, explanted from 1 to 7 somites, developed a blood circulation
(72%) and 3 3 % reached the limb-bud stage. Rat embryos, explanted
from 6 to 12 somites stages, differentiated fore-limbs and 25 to 30
somites.
D .
R E I M P L A N T A T I O N
O F E G G S I N T H E U T E R U S
A F T E R
E X P E R I M E N T S
W I T H
T H E M
I N IJV VITRO
C U L T U R E
Since it has proved impossible to continue development of eggs for
a long period in vitro, several authors have reimplanted mammalian
eggs into the uterus after a period in vitro. Eggs have been reimplanted
either directly after they were removed or after a certain time in
culture.
The first type of investigation (implantation directly after removal)
was inaugurated by Nicholas and Hall (1934, 1942). These authors
separated the first two blastomeres from an egg of a rat; each of the
two blastomeres could give rise to a complete embryo. Two juxtaposed
eggs developed into a single embryo, properly proportioned but double
the size of a normal one. Analogous experiments with regard to the