Mitotic cells and their microappendages in the primitive streak of the chick embryo

Fresh pullet eggs (White Leghorn Strain) were incubated to the primitive streak stage of development. Blastoderms were fixed in situ with isotonic aldehyde fixatives and prepared for scanning electron miscroscopy by means of post‐osmication, critical point drying and gold‐palladium coating. Cells judged to be in various stages of mitosis by their surface contours were numerous on the ventral surface of the chick blastoderm. Cells which were in the late preparatory stages for mitosis had rounded up from their surroundings. Microvilli dominated the surface. The degree of separation and number of microvilli increased until late metaphase or anaphase. Mitotic cells did not completely separate themselves from adjacent cells. Ruffles and blebs were not prominent during mitotis and long filopodia were absent. A definite localization of microappendages (microvilli, blebs, ruffles) to the area of cytokinesis was evident in early telophase and persisted through daughter cell formation.