Mitosis in the formation and function of the primary hypoblast of the chick.

The present work demonstrates that a normal stage-XIII hypoblast, if submitted to an X-ray dose of 6,000 rads (sufficient to stop cell division), retains the capacity to induce axis formation on the chick epiblast. Examination of the process of hypoblast formation indicates, in agreement with previous findings, that a hypoblastic layer can form in the absence of cell division from an irradiated stage-X blastoderm. Furthermore, it is observed that this hypoblastic layer, formed in the absence of cell division, can induce the development of an embryonic axis when combined with a normal stage-XIII epiblast.