Induction by Regions lateral to the Streak in the Chick Embryo

The discovery of the organization centre of Amphibia by Spemann (1918) opened a new field in the outlook of experimental embryology; but there were several technical difficulties to be overcome in the application of the concept of the organizer to avian embryology. In this connexion the tissue culture technique has several advantages over the earlier methods of in situ sectioning or chorio-allantoic techniques, and it has helped a great deal in the understanding of the processes of development in the chick. It has already been proved that at least the anterior third of the primitive streak has an organizing function (Waddington, 1932); but regions outside the primitive streak have not been systematically tested so far for the inducing capacity. In the present studies an attempt is made to study the extent of the organization centre in the chick embryo at the definitive primitive streak stage.