Historical overview

The notion of mesectoderm

Kastschenko (1888) first reported that the neural crest is the source of mesenchymal cells in selacians. Soon after, Goronowitsch (1892, 1893) extended this notion to teleosts and birds. At the same time, Platt (1893, 1897), found that the mesenchymal cells forming the cartilage of the visceral arches and the dentine of the teeth were derived from the dorsal ectoderm of the head. She created the term “mesectoderm” for the mesenchyme of ectodermal origin, in contrast to the mesodermal mesenchyme which she called “mesentoderm.” Nowadays, the term “ectomesenchyme” is often used to designate the mesenchymal cells derived from the neural crest. These findings were not immediately accepted and gave rise to a controversy reflecting how vigourous von Baer's germ layer theory was. Von Baer had pointed out in 1828 that homologous structures in different animals are derived from material belonging to the same germ layers; according to this view, the mesenchyme could arise only from mesoderm. It was not until the 1920s that thorough morphological observations and experimental work, carried out primarily in amphibians (Landacre, 1921; Stone, 1922, 1926, 1929), led to the unambiguous demonstration that a significant proportion of the mesenchymal cells of the body were actually derived from the ectodermal germ layer.

For many years the extent to which the neural crest generates mesenchymal derivatives was studied mostly in lower vertebrates.