15. E M B R Y O G E N E S I S in vitro
533
explantation of embryonic tissues from various species of animals. It
has the following composition:
Holtfreter's solution:
This solution, it may be noted, is a simple physiological salt solution,
adapted for embryonic tissues of amphibians. No nutritive components
at all are involved, in contrast to the culture media for embryonic tissues
of birds and of Mammalia. In fact, the cells of even fairly well-developed
amphibian embryos contain sufficient reserves of yolk to allow their
survival and differentiation.
Slight modifications of Holtfreter's solution were made by Niu and
Twitty (1953) with the use of Flickinger's solution, and by V o n Woellwarth (1956). These modifications somewhat improved the culture
of particularly delicate tissues, and of isolated cells.
Two principal lines of investigation have been pursued by Holtfreter
and his followers. (1) The potentialities of the isolated anlage of the
young gastrula were tested by simple explantation into the medium.
(2) The inducing powers of many tissues and substances were explored
by means ofthe "ectodermal sandwiches" method. This technique consists of explanting a large piece of presumptive ectoderm taken from the
animal region of the young gastrula, and of wrapping it round a fragment of the tissue or a sample of the substance which one wishes to test
for its organizing power.
B. D E T E R M I N A T I O N A N D S E L F - D I F F E R E N T I A T I O N OF
D E V E L O P M E N T A L REGIONS OF T H E Y O U N G G A S T R U L A
Holtfreter (1938) marked out three regions of the embryo whose
potentialities are essentially different: the region of the primary
ectoblast (presumptive epidermis and neural tissue); the external
marginal zone (presumptive chorda-mesoderm), and the internal
marginal zone of the endoderm (Fig. 1).
1. The Region of the Primary Ectoblast (Presumptive Epidermis and Neural
This region shows no determination at all when it is taken out at the
beginning of gastrulation. It gives atypical epidermal structures and
never gives rise to any nervous tissue. Floating in the medium, it forms
a folded, bloated vesicle like the one which results from exogastrulation.
NaCl
KC1
CaCl 2
0-35 g
0-005 g
0-01 g
0-02 g
100 ml
N a H C 0 3
H 2 0
Anlage)
533
explantation of embryonic tissues from various species of animals. It
has the following composition:
Holtfreter's solution:
This solution, it may be noted, is a simple physiological salt solution,
adapted for embryonic tissues of amphibians. No nutritive components
at all are involved, in contrast to the culture media for embryonic tissues
of birds and of Mammalia. In fact, the cells of even fairly well-developed
amphibian embryos contain sufficient reserves of yolk to allow their
survival and differentiation.
Slight modifications of Holtfreter's solution were made by Niu and
Twitty (1953) with the use of Flickinger's solution, and by V o n Woellwarth (1956). These modifications somewhat improved the culture
of particularly delicate tissues, and of isolated cells.
Two principal lines of investigation have been pursued by Holtfreter
and his followers. (1) The potentialities of the isolated anlage of the
young gastrula were tested by simple explantation into the medium.
(2) The inducing powers of many tissues and substances were explored
by means ofthe "ectodermal sandwiches" method. This technique consists of explanting a large piece of presumptive ectoderm taken from the
animal region of the young gastrula, and of wrapping it round a fragment of the tissue or a sample of the substance which one wishes to test
for its organizing power.
B. D E T E R M I N A T I O N A N D S E L F - D I F F E R E N T I A T I O N OF
D E V E L O P M E N T A L REGIONS OF T H E Y O U N G G A S T R U L A
Holtfreter (1938) marked out three regions of the embryo whose
potentialities are essentially different: the region of the primary
ectoblast (presumptive epidermis and neural tissue); the external
marginal zone (presumptive chorda-mesoderm), and the internal
marginal zone of the endoderm (Fig. 1).
1. The Region of the Primary Ectoblast (Presumptive Epidermis and Neural
This region shows no determination at all when it is taken out at the
beginning of gastrulation. It gives atypical epidermal structures and
never gives rise to any nervous tissue. Floating in the medium, it forms
a folded, bloated vesicle like the one which results from exogastrulation.
NaCl
KC1
CaCl 2
0-35 g
0-005 g
0-01 g
0-02 g
100 ml
N a H C 0 3
H 2 0
Anlage)