Primary neurulation in teleosts--evidence for epithelial genesis of central nervous tissue as in other vertebrates.

Early teleostian embryos were studied by scanning electron microscopy. Transversal and longitudinal views of the neural anlage clearly demonstrate that it has an ordinary epithelial organization consisting of parallel columnar cells. Unless it has been supposed earlier, there is no solid thickened neural plate but the neural ectoderm is tightly folded forming a very narrow neural groove. Thus, primary neurulation in teleosts is shown to occur similar to that in other vertebrates viz. by folding of the neural plate to get the neural tube. That means that the neuroepithelial cells retain their polarity instead to become organized from a randomly oriented mass of unpolarized cells, as it is thought to occur in secondary neurulation.