Endoderm regeneration in the chick embryo studied by SEM.

Regeneration of the area pellucida endoderm of the chick embryo was studied by scanning electron microscopy (SEM). A new endoderm was formed by in situ changes in the shape and relationships of mesoderm cells. Initially the cells flattened and lost their processes except along cell boundaries. Later even these processes were lost and an epithelium was formed. The area of regenerated endoderm coincided with the area of mesoderm at the time of endoderm removal, confirming the mesodermal origin of the new layer. Remnants of the original endoderm did not contribute to the regenerated layer. Contact inhibition was observed at the boundary between original and regenerated endoderms.