Which Statement About Animal Development Is False?
A) Signaling Molecules $\beta$

Multiple Choice

Which statement about animal development is false?

A) Signaling molecules interact to produce different combinations of signals that eventually guide embryonic cells to differentiate along different pathways.
B) $\beta$ -catenin is necessary but not sufficient for the formation of the primary embryonic organizer.
C) Expression of embryonic genes usually begins just before gastrulation.
D) The mouth of the sea urchin forms where the archenteron makes contact with the ectoderm.
E) Cells can actively migrate during gastrulation.