Which of the following best illustrates "feedback" in development?

Feedback in development is illustrated by “as tissue X develops, it secretes something that induces tissue Y to develop.”

Induction is the process by which one tissue (inducing tissue) stimulates the development of an adjacent unspecialised tissue (responding tissue). The inducing tissue usually produces a chemical substance that influences the development of the responding tissue.

During embryonic development, mesodermal cells from the primitive node migrate toward the head end of the embryo and form a hollow tube of cells in the midline called the notochordal process . By days 22–24, the notochordal process becomes a solid  cylinder of cells called the notochord. The notochord induces certain mesodermal cells to develop into the vertebral bodies. It also forms the nucleus pulposus of the intervertebral discs. The notochordal process also induces the overlying ectoderm to develop into a neural plate.