Animal Development

Starfish Development

Black arrowhead: unfertilized ovum.

Red arrow: fertilized ovum

Black arrow: 8-cell stage.

White arrowhead: morula stage.

Starfish Development

Black arrowhead: blastula.

White arrowhead: invagination.

Black arrow: early gastrula.

Starfish Development

Red arrow: two-cell stage.

Green arrow: four-cell stage
(note that cleavage is equal)

Black arrowhead: late gastrula.

Black arrow: bipinnaria.

Note (blue arrow) the secondary
formation of the mouth
(blastopore becomes the anus).

Frog Development

2-cell stage

Black arrow: cleavage furrow
beginning at animal pole.

Frog Development

Morula

Black arrowhead: micromeres.

Black arrow: macromeres.

Red arrow: blastocoel.

Note that the embryo is rotated
about 45 degrees clockwise
so that the animal pole is
to the right

Frog Development

Blastula

Black arrow: blastocoel.

Frog Development

Early Gastrula

Black arrow: blastocoel.

Black arrowhead: yolk plug.

Note: the colors on the arrows
showing the processes
of gastrulation do NOT
correspond to the
germ layers indicated.

Frog Development

Gastrula

Black arrow: blastocoel.

Black arrowhead: archenteron.

Blue arrow: presumptive
neural plate.

Green arrow: presumptive
notochord.

Yellow arrow: yolk plug.

Red arrow: blastopore
(occluded by
yolk plug).

Frog Development

Early Neurula

Black arrowhead: neural groove.

Black arrow: neural fold.

Frog Development

Neurula

Black arrow: neural tube.

Chick Development

Primitive Streak

Neural folds.

Chick Development

33-hours

Black arrow: optical vesicle.

Black arrowhead: somite.

White arrow: heart.

White arrowhead: neural fold.

Chick Development

48-hours

Black arrow: neural tube.

Black arrowhead: notochord.