Applications of the SEM to the analysis of morphogenetic events.

Scanning electron microscopy (SEM) is a valuable tool for the analysis of morphogenetic events. The role of extracellular materials in primary neural induction in the early stage 5 chick embryo may be analysed by SEM as well as by histochemical techniques. During primary neural induction, extracellular materials in the early stage 5 chick embryo form a fan-shaped region on the ectoderm anterior to Hensen's node. Fibronectin and sulphated glycosaminoglycans are present anterior to Hensen's node on the ventral ectoderm layer. It is proposed that the fanshape of extracellular materials has a dual function; as a chemical substrate to form close contacts between the inducing cells and the target ectoderm cells, and to serve as a contact guidance system of the pre-notochordal cells.