Ch. 47—Animal Development

Fertilization

Fertilization

Fertilization

Fertilization

Once fertilization is complete

Animal Development

• Cleavage—rapid mitotic cell division into smaller cells—blastomeres

• Solid ball of cells—morula• Blastula produced when a

cavity called blastocoel forms

• Gastrulation—rearrangement of cells into 3 germ layers

blastomeres

Morula (solid ball of cells)

Blastocyst• Blastula stage of

mammalian embryos• Trophoblast layer

enclosing the blastocoel– Chorion (outer

embryonic layer)

Blastocyst develops into gastrula

Gastrulation• Cells rearrange and fold inward at the blastopore to form a gastrula with three-germ layers:– Ectoderm (skin, nails, teeth)– Mesoderm (skeletal, muscular, excretory, circulatory, reproductive

systems; blood, bone, and muscle)– Endoderm (epithelial lining of digestive, respiratory, excretory

tracts; liver, pancreas)

Organogenesis• Development of 3 germ

layers into the beginnings of organs– Notochord—stiff dorsal

skeletal rod (from mesoderm)– Neural plate—will become

brain and spinal cord (from ectoderm)

– Somites—blocks of mesoderm arranged along notochord; sign of segmentation

Amniotes• Amnion—fluid filled cavity; protects embryo• Allantois—disposal sac• Chorion—exchange gases• Yolk sac—provides nutrients

Eutherian mammals