Scanning electron microscopical and histochemical study of the endoderm in the early chick embryo.

The endoderm of gastrulating chick embryos shows regional variations in cell shape and size. These were studied by scanning electron microscopy, histochemistry and immunofluorescence. Particular attention was given to the distribution of the cytoskeleton. Four zones of differing morphology were observed. The changing size and shape of these zones could be correlated with the entry of the definitive endoblast through the primitive streak, displacing existing primary hypoblast to the edges of the area pellucida. Endodermal cells were shown to have a well organised cytoskeleton. The cytoskeletons of individual cells were linked to give a cytoskeletal network extending across the endoderm as a whole.