Chapter 19 - Genes, Development, and Evolution - 19.2 - Gene Expression Differences Determine Cell Fate and Cell Differentiation - 19.2 Recap - Learning Outcomes - Page 409: 2

The developing forebrain of a frog embryo protrudes out at both sides to form the optic vesicles. These vesicles expand until they touch the cells at the top of the head, which thickens and forms a lens placode that will eventually become the lens. If the developing optic vesicle is removed before it contacts the surface cells, the lens will be unable to form, suggesting that the surface tissue develops into a lens only after it receives a cellular signal, or inducer, from the optic vesicle.

The developing forebrain of a frog embryo protrudes out at both sides to form the optic vesicles. These vesicles expand until they touch the cells at the top of the head, which thickens and forms a lens placode that will eventually become the lens. If the developing optic vesicle is removed before it contacts the surface cells, the lens will be unable to form, suggesting that the surface tissue develops into a lens only after it receives a cellular signal, or inducer, from the optic vesicle.