Primitive Streak; homologous to amphibian blastopore lip

TLS Online TPP Program

#Id: 1604

#Unit 5. Developmental Biology

Amniote cell specification (germ layer identity)is established before gastrulation starts, but the specification of cell type is controlled by inductive influences during and after migration through the primitive streak.

TLS Online TPP Program

#Id: 1605

#Unit 5. Developmental Biology

Cells passing through the more anterior portions of the primitive streak give rise to the endoderm, head mesoderm, and notochord.

TLS Online TPP Program

#Id: 1606

#Unit 5. Developmental Biology

Cells passing through the more posterior portions of the primitive streak give rise to the majority of mesodermal tissues.

TLS Online TPP Program

#Id: 2350

#Unit 5. Developmental Biology

Planarian flatworms can reproduce asexually by binary fission, during which they split themselves in half.

TLS Online TPP Program

#Id: 2351

#Unit 5. Developmental Biology

If the planarian is cut in half, the anterior portion of the lower half regenerates a head while the posterior of the upper half regenerates a tail. 

TLS Online TPP Program

#Id: 2352

#Unit 5. Developmental Biology

If a flatworm is cut into three pieces, the middle piece will regenerate a head from its anterior end and a tail from its posterior end.