Studies on the Development of the Foregut in the Chick Blastoderm: 2. The Morphogenetic Movements

The first of this series of papers (Bellairs, 1953) outlined the morphological changes occurring in the endoderm of the chick up to the stage of about ten pairs of somites; it also showed that the presumptive foregut area in the primitive streak stage blastoderm lies around the anterior end of the primitive streak, and at a slightly later stage around the head process. The present paper is concerned with the pattern of morphogenetic movements which occur in the endoderm during the early stages of foregut development. The technique involved the use of carbon marks upon the exposed endoderm of blastoderms grown dorsal side downwards in tissue culture by the watchglass method (Waddington, 1932; Bellairs, 1953). During the period of development investigated an expansion of the blastoderm as a whole took place over the plasma clot; the use of external reference points was therefore essential, although even with such aids it was not always possible to tell whether certain displacements of marked cells were in fact merely the expression of a general expansion or were due to a specific morphogenetic migration.