50. LE 47-18b
Hypoblast
Chorion (from
trophoblast
Epiblast
Amniotic
cavity
Amnion
Yolk sac (from
hypoblast)
Extraembryonic mesoderm cells
(from epiblast)
Extraembryonic
membranes start
to form and
gastrulation
begins.
Amnion
Chorion
Endoderm
Mesoderm
Ectoderm
Yolk sac
Extraembryonic
mesoderm
Gastrulation has produced a
three-layered embryo with four
extraembryonic membranes.
Allantois
Expanding
region of
trophoblast
63. LE 47-23a
Fate map of a frog embryo
Epidermis Central
nervous
system
Blastula
Epidermis
Neural tube stage
(transverse section)
Endoderm
Mesoderm
Notochord
70. LE 47-24
Left (control):
Fertilized
salamander eggs
were allowed to
divide normally,
resulting in the
gray crescent
being evenly
divided between
the two blastomeres.
Right (experimental):
Fertilized eggs were
constricted by a
thread so that the
first cleavage plane
restricted the gray
crescent to one
blastomere.
Gray
crescent
Gray
crescent
Normal Belly
piece
Normal
The two blastomeres were
then separated and
allowed to develop.