User:Jtwsaddress42/Quotes/Hall, Brian K. 2000a

The Neural Crest as a Fourth Germ Layer And Vertebrates as Quadroblastic Not Triploblastic "'...[N]eural crest cells are not a homogenous population of cells, but rather a collective of populations of cells. Although they overlap in the neural crest, some of these cell populations have been separate since the origin of the vertebrates almost 500 million years ago... [N]eural crest cells transform to mesenchyinal cells and migrate away from the developing brain and spinal cord, migrating as discrete populations of cells. Similar populations of cells can be observed across the vertebrates, i.e.. they have been conserved throughout vertebrate evolution. The neural crest gives rise to so many different cell types - more types than arise from mesoderm - that the neural crest can be regarded as a fourth germ layer, one that is unique to vertebrates and that allowed many distinctive vertebrate tissues to arise.'

Brian K. Hall (2000)"